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Thyroid function and risk of type 2 diabetes: A population-based prospective cohort study

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  • Erasmus University Rotterdam and Harvard TH Chan School of Public Health

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Background: The association of thyroid function with risk of type 2 diabetes remains elusive. We aimed to investigate the association of thyroid function with incident diabetes and progression from prediabetes to diabetes in a population-based prospective cohort study. Methods: We included 8452 participants (mean age 65 years) with thyroid function measurement, defined by thyroid-stimulating hormone (TSH) and free thyroxine (FT4), and longitudinal assessment of diabetes incidence. Cox-models were used to investigate the association of TSH and FT4 with diabetes and progression from prediabetes to diabetes. Multivariable models were adjusted for age, sex, high-density lipoprotein cholesterol, and glucose at baseline, amongst others. Results: During a mean follow-up of 7.9 years, 798 diabetes cases occurred. Higher TSH levels were associated with a higher diabetes risk (hazard ratio [HR] 1.13; 95 % confidence interval [CI], 1.08-1.18, per logTSH), even within the reference range of thyroid function (HR 1.24; 95 % CI, 1.06-1.45). Higher FT4 levels were associated with a lower diabetes risk amongst all participants (HR 0.96; 95 % CI, 0.93-0.99, per 1 pmol/L) and in participants within the reference range of thyroid function (HR 0.96; 95 % CI, 0.92-0.99). The risk of progression from prediabetes to diabetes was higher with low-normal thyroid function (HR 1.32; 95 % CI, 1.06-1.64 for TSH and HR 0.91; 95 % CI, 0.86-0.97 for FT4). Absolute risk of developing diabetes type 2 in participants with prediabetes decreased from 35 % to almost 15 % with higher FT4 levels within the normal range. Conclusions: Low and low-normal thyroid function are risk factors for incident diabetes, especially in individuals with prediabetes. Future studies should investigate whether screening for and treatment of (subclinical) hypothyroidism is beneficial in subjects at risk of developing diabetes.
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R E S E A R C H A R T I C L E Open Access
Thyroid function and risk of type 2
diabetes: a population-based prospective
cohort study
Layal Chaker
1,2,3
, Symen Ligthart
3
, Tim I. M. Korevaar
1,2,3
, Albert Hofman
3,4
, Oscar H. Franco
3
,
Robin P. Peeters
1,2,3*
and Abbas Dehghan
3
Abstract
Background: The association of thyroid function with risk of type 2 diabetes remains elusive. We aimed to
investigate the association of thyroid function with incident diabetes and progression from prediabetes to
diabetes in a population-based prospective cohort study.
Methods: We included 8452 participants (mean age 65 years) with thyroid function measurement, defined by
thyroid-stimulating hormone (TSH) and free thyroxine (FT4), and longitudinal assessment of diabetes incidence.
Cox-models were used to investigate the association of TSH and FT4 with diabetes and progression from
prediabetes to diabetes. Multivariable models were adjusted for age, sex, high-density lipoprotein cholesterol,
and glucose at baseline, amongst others.
Results: During a mean follow-up of 7.9 years, 798 diabetes cases occurred. Higher TSH levels were associated
with a higher diabetes risk (hazard ratio [HR] 1.13; 95 % confidence interval [CI], 1.081.18, per logTSH), even
within the reference range of thyroid function (HR 1.24; 95 % CI, 1.061.45). Higher FT4 levels were associated
with a lower diabetes risk amongst all participants (HR 0.96; 95 % CI, 0.930.99, per 1 pmol/L) and in participants
within the reference range of thyroid function (HR 0.96; 95 % CI, 0.920.99). The risk of progression from prediabetes
to diabetes was higher with low-normal thyroid function (HR 1.32; 95 % CI, 1.061.64 for TSH and HR 0.91; 95 % CI,
0.860.97 for FT4). Absolute risk of developing diabetes type 2 in participants with prediabetes decreased from
35 % to almost 15 % with higher FT4 levels within the normal range.
Conclusions: Low and low-normal thyroid function are risk factors for incident diabetes, especially in individuals with
prediabetes. Future studies should investigate whether screening for and treatment of (subclinical) hypothyroidism is
beneficial in subjects at risk of developing diabetes.
Keywords: Type 2 diabetes, Thyroid hormone, Thyroid function, Diabetes, Prediabetes
Background
Diabetes mellitus and thyroid disease are the two most
common endocrine disorders, often co-existing in patients
[1]. The role of auto-immunity has been well-recognized
in the link between auto-immune thyroid disease and
type 1 diabetes mellitus [2]. A relation between thyroid
dysfunction and type 2 diabetes mellitus has also been
suggested, but the possible underlying mechanisms and
drivers show complex interactions [3].
Thyroid hormone is a major regulator of metabolism
and energy expenditure, is directly involved in the con-
trol of insulin secretion and glucose homeostasis [3, 4],
and has been shown to preserve beta-cell viability and
proliferation [5, 6]. Hyperthyroid individuals have an in-
creased insulin secretion [7] and higher free triiodothyron-
ine levels are specifically associated with improved insulin
secretion in individuals with prediabetes [8]. However, the
deleterious effect of thyrotoxicosis on glucose metabolism
* Correspondence: r.peeters@erasmusmc.nl
Equal contributors
1
Rotterdam Thyroid Center, Erasmus University Medical Center, Rotterdam,
The Netherlands
2
Department of Internal Medicine, Erasmus University Medical Center,
Rotterdam, The Netherlands
Full list of author information is available at the end of the article
© 2016 The Author(s). Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Chaker et al. BMC Medicine (2016) 14:150
DOI 10.1186/s12916-016-0693-4
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has also been recognized for decades [9]. Excess thyroid
hormone (i.e. hyperthyroidism) causes increased liver
gluconeogenesis and peripheral insulin resistance and
is associated with glucose intolerance [1013]. Interest-
ingly, lack of thyroid hormone is also associated with a
decrease in peripheral insulin sensitivity and glucose
intolerance [14] and treatment of hypothyroidism has
been shown to improve insulin sensitivity [14, 15].
There are several cross-sectional reports on the associ-
ation between thyroid dysfunction and diabetes, albeit
with conflicting results, with some studies reporting an
association between hyperthyroidism and type 2 dia-
betes, while others report instead an association between
hypothyroidism and diabetes. Further, one of the most
recent and largest cross-sectional studies reports no
association between thyroid dysfunction and type 2
diabetes [16]. However, cross-sectional studies have sev-
eral limitations, including lack of assessment of temporal-
ity. Only few studies have investigated the association of
thyroid function with incidence of diabetes prospectively
and all were register-based studies, again reporting
conflicting results [1719]. As a consequence, there is
no consensus regarding whether patients with thyroid
dysfunction should be screened for diabetes. To date,
there are no prospective population-based cohort stud-
ies investigating the association across the full range of
thyroid function, including the normal range, with the
risk of diabetes. Therefore, we aimed to investigate the
association of thyroid function with the incidence of
type 2 diabetes and the progression from prediabetes to
diabetes in the Rotterdam Study, a large prospective
population-based cohort study.
Methods
The Rotterdam Study
The Rotterdam Study is a prospective population-based
cohort study that investigates the determinants and occur-
rence of age-related diseases in Ommoord, Rotterdam, the
Netherlands. The aims and design of the Rotterdam Study
have been described in detail elsewhere [20]. The Rotter-
dam Study consists of three independent cohorts: RS Co-
hort I (RSI), including 7983 participants aged 55 years
(baseline 19901993), RS Cohort II (RSII), including 3011
participants aged 55 years (baseline 20002001), and
RS Cohort III (RSIII), including 3932 participants
aged 45 years (baseline 20062008).
The Rotterdam Study has been approved by the medical
ethics committee according to the Population Screening
Act: Rotterdam Study, executed by the Ministry of Health,
Welfare and Sports of the Netherlands.
Study population
We selected data from participants from the third visit
of the first cohort (19971999, n= 4797) and the first
visit of the second (20002001, n= 3011) and third
(20062008, n= 3932) cohorts, if thyroid-stimulating
hormone (TSH) or free thyroxine (FT4) measurements,
which were performed in a random set of participants,
and information on diabetes were available. All partici-
pants in the present analysis provided written informed
consent to participate and to obtain information from
their treating physician. All study participants were
followed up from the day of baseline laboratory testing
to date of onset of diabetes, to death, or to January 1,
2012, whichever came first.
Assessment of thyroid function
Thyroid function was measured using the same methods
and assay for all three cohorts, and samples were col-
lected between 1997 and 2008, depending on the cohort.
TSH and FT4 measurements were performed in serum
samples stored at 80 °C (electrochemiluminescence
immunoassay for thyroxine and thyrotropin, ECLIA,
Roche). We determined cut-off values for the reference
range of TSH as 0.44.0 mIU/L and for FT4 as 1125
pmol/L (0.861.94 ng/dL) according to guidelines as
well as our previous studies [21]. Thyroid peroxidase
antibody (TPOAb) levels greater than 35 kU/mL were
regarded as positive, as recommended by the assay
manufacturer (electrochemiluminescence immunoassay
for thyroid peroxidase antibodies, ECLIA,Roche).
Ascertainment of prediabetes and type 2 diabetes
At baseline and during follow-up, cases of prediabetes
and type 2 diabetes were ascertained through active
follow-up using general practitionersrecords, hospital dis-
charge letters, and serum glucose measurements from Rot-
terdam Study visits, which take place approximately every
4 years [22]. Normoglycemia, prediabetes, and diabetes
were defined according to recent WHO guidelines [23];
normoglycemia was defined as a fasting serum glucose <
6.0 mmol/L; prediabetes was defined as a fasting serum glu-
cose > 6.0 mmol/L and < 7.0 mmol/L or a non-fasting
serum glucose > 7.7 mmol/L and < 11.1 mmol/L (when fast-
ing samples were absent); and type 2 diabetes was defined
as a fasting serum glucose 7.0 mmol/L, a non-fasting
serum glucose 11.1 mmol/L (when fasting samples were
absent), or the use of blood glucose lowering medication.
Information regarding the use of blood glucose lowering
medication was derived from both structured home inter-
views and linkage to pharmacy records. At baseline, more
than 95 % of the Rotterdam Study population was covered
by the pharmacies in the study area. All potential events of
type 2 diabetes were independently adjudicated by two
study physicians. In case of disagreement, consensus was
sought with an endocrinologist [22].
Chaker et al. BMC Medicine (2016) 14:150 Page 2 of 8
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Baseline measurements
Body mass index was calculated as body mass (kg) di-
vided by the square of the body height (m). Serum HDL
cholesterol and glucose were measured using standard
laboratory techniques. Information on tobacco smoking
was derived from baseline questionnaires. Systolic and
diastolic blood pressure was calculated as the average of
two consecutive measurements. Insulin was measured
using an immunoassay (electrochemiluminescence im-
munoassay ECLIA, Roche). Over 95 % of participants
were in a fasting state when blood was drawn at the
Rotterdam Study center visit. Information on medication
use was obtained from questionnaires in combination with
pharmacy records. Thyroid medication, including thyroid
hormone replacement therapy, was prescribed by par-
ticipants own GP or specialist and within the context
of regular treatment and blinded to measurements of
the Rotterdam Study.
Statistical methods
We used Cox-proportional hazards models to assess the
association of TSH or FT4 with incident diabetes. We
also assessed the association of thyroid function mea-
surements and incident diabetes in participants with
prediabetes separately. We first conducted these analyses
in all included participants and then only in those with
normal TSH and FT4 values, after excluding levothyroxine
users. The primary model, model 1, was adjusted for age,
sex, cohort, fasting glucose, and tobacco smoking. Model
2 was additionally adjusted for possible confounders or
intermediate factors, including fasting serum insulin, sys-
tolic blood pressure, diastolic blood pressure, use of blood
pressure lowering medication (diuretics, anti-adrenergic
agents, βblockers, calcium channel blockers, and RAAS
inhibitors), high-density lipoprotein (HDL) cholesterol
and body mass index (BMI). Adjusting for both BMI and
waist circumference showed multicollinearity in the
model, with BMI providing the best model fit. Additionally
adjusting for waist circumference next to BMI did not
provide meaningful changes in the risk estimates and
therefore waist circumference was omitted from the
model. Furthermore, we assessed the association of TSH
and FT4 tertiles in the normal reference range with
progression from prediabetes to diabetes and calculated
absolute risk estimates for the tertiles, using the covari-
ates of the multivariable model. We performed the fol-
lowing sensitivity analyses: (1) excluding participants
using levothyroxine at baseline, (2) excluding participants
using thyroid function altering medication, including
levothyroxine, anti-thyroid drugs (e.g., thiamazole), amio-
darone, and corticosteroids at baseline and follow-up, and
(3) additionally excluding participants with TSH and
FT4 values outside the normal range. We stratified by
possible effect modifiers, including age categories (cut-off
of 65 years) and sex. The natural logarithm of TSH was
used for the continuous models and results are presented
Fig. 1 Participant selection
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per doubling of TSH on average. The proportional hazards
assumption was assessed by performing Schoenfeld tests
and plots and was met for all analyses. There was no de-
parture from linearity as assessed by restricted cubic
splines or adding quadratic terms of TSH, FT4, or age to
the model. Reporting of the results is according to the
STROBE statement.
Results
We included a total of 8452 participants with thyroid
function measurements and who were free of diabetes at
baseline (Fig. 1). The mean age of the included partici-
pants was 64.9 years and 58 % were female. Baseline char-
acteristics are shown in Table 1. During a mean follow-up
of 7.9 years (standard deviation 4.0 years), 798 individuals
developed diabetes (IR 12 per 1000 person-years). Com-
pleteness of follow-up was 99.4 % [24].
Thyroid function and incident diabetes
The associated risk of developing diabetes was 1.09
times higher for every doubling of TSH levels mIU/L
(95 % confidence interval [CI], 1.061.12; Table 2).
Within the normal range, the risk of diabetes was 1.16
times higher with higher TSH levels. In model 2, this as-
sociation attenuated slightly (hazard ratio [HR] 1.06;
95 % CI, 1.001.13, Table 2). In the most adjusted model
(model 2), higher FT4 levels were associated with a de-
creased risk of diabetes (HR 0.96; 95 % CI, 0.930.99), also
within the normal range (HR 0.94; 95 % CI, 0.900.98).
Table 1 Baseline characteristics of included participants
Variable Mean (SD)*
Number of individuals in the study 8452
Age, in years 64.6 (9.7)
Female, n(%) 4899 (58.0)
BMI, kg/m
2
26.5 (4.05)
Total cholesterol, mmol/L 5.76 (1.01)
HDL cholesterol, mmol/L 1.43 (0.41)
Smoking, n(%)
Current 1742 (20.6)
Former 4020 (47.6)
Never 2691 (31.8)
Systolic blood pressure, mmHg 139 (21)
Diastolic blood pressure, mmHg 79 (11)
Antihypertensive medication use, n(%) 1881 (22.3)
TSH, median (IQR) 1.91 (1.292.76)
FT4, pmol/L 15.7 (2.32)
TPOAb positivity, n(%) 1119 (13.2)
Levothyroxine use, n(%) 233 (2.8)
*unless specified otherwise
TPOAb levels >35 kU/mL were regarded as positive
BMI body mass index, IQR interquartile range, FT4 free thyroxine, SD standard
deviation, TPOAb thyroid peroxidase antibodies, TSH thyroid-stimulating hormone,
nnumber
Table 2 Association between thyroid function and the risk of incident prediabetes and diabetes
Thyroid function measurements HR (95 % CI) Model 1 HR (95 % CI) Model 2 Incident cases Total participants
Incident Diabetes
Full range of measurement
TSH mIU/L 1.09 (1.061.12) 1.06 (1.001.13) 798 8447
Free T4 pmol/L 0.96 (0.930.99) 0.96 (0.930.99) 797 8446
Normal TSH and FT4 values
TSH mIU/L 1.16 (1.041.30) 1.14 (1.021.27) 685 7188
Free T4 pmol/L 0.96 (0.920.99) 0.94 (0.900.98) 685 7188
Progression from prediabetes to diabetes
Full range of measurement
TSH mIU/L 1.17 (1.071.27) 1.13 (1.031.24) 412 1337
Free T4 pmol/L 0.92 (0.890.97) 0.93 (0.890.98) 411 1336
Normal TSH and FT4 values
TSH mIU/L 1.26 (1.081.47) 1.21 (1.041.41) 358 1137
Free T4 pmol/L 0.90 (0.850.95) 0.91 (0.860.97) 358 1137
Model 1: adjusted for sex, age, smoking, fasting serum glucose levels and cohort
Model 2: adjusted for sex, age, smoking, cohort, fasting serum glucose levels, fasting serum insulin measurements, systolic blood pressure, diastolic blood
pressure, blood pressure lowering medication, HDL cholesterol, and body mass index
Normal range of TSH is defined by 0.44.0 mIU/L and normal range FT4 is defined by 1125 pmol/L and participants not using levothyroxine
Results are presented as HR per doubling of TSH on average and per one increase in pmol/L of FT4
CI confidence interval, FT4 free thyroxine, HR hazard ratio, TSH thyroid-stimulating hormone
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Sensitivity analyses did not change risk estimates
meaningfully (Additional file 1: Table S1). Stratifying the
analyses by age category or sex did not show effect
modification for incident diabetes (Pfor interaction > 0.05
for all).
Thyroid function and progression of prediabetes to
diabetes
In participants with prediabetes, the associated risk of
developing diabetes was 1.13 times higher for every
doubling of TSH levels (95 % CI, 1.031.24; Table 2).
The risk of incident diabetes in participants with predia-
betes was 0.93 times lower with each 1 pmol/L increase
of FT4 (95 % CI, 0.890.98). In the normal range, the
risk of developing diabetes was 1.44 times higher (95 % CI,
1.131.93) when comparing the highest to the lowest ter-
tile of TSH in the normal range in model 1 (Additional file
2: Table S2). This corresponds to an absolute risk differ-
ence of 8.5 % for a follow-up of 7 years. Comparing the
highest to the lowest tertile for FT4, the HR for developing
diabetes in individuals with prediabetes was 0.63 (95 % CI,
0.480.82; Additional file 2: Table S2). Additionally
adjusting analyses for TPOAb positivity did not change
risk estimates meaningfully (data not shown). This cor-
responds to a 1.59 times higher risk and an absolute
risk difference of 9.6 % of progression to diabetes when
comparing the lowest to the highest tertile of FT4
(Additional file 2: Table S2). These associations attenuated
only slightly in model 2 (Fig. 2, Additional file 2: Table S2).
Absolute risk of diabetes type 2 in participants with predi-
abetes decreased from 35 % to almost 15 % with higher
FT4 levels within the normal range (Fig. 3).
Discussion
To our knowledge, this is the first prospective population-
based cohort study describing the relation between thyroid
function within the normal range and the risk of diabetes
and progression from prediabetes and type 2 diabetes.
Higher TSH levels and lower FT4 levels are associated
with an increased risk of diabetes and progression from
prediabetes to diabetes.
Fig. 2 Association of thyroid-stimulating hormone (TSH) and free thyroxine (FT4) levels in tertiles within the normal range and incident diabetes
in individuals with prediabetes. The normal range of TSH was defined as 0.44.0 mIU/L and of FT4 as 1125 pmol/L (Conversion 1 pmol/L = 0.0777 ng/dL),
thyroid hormone medication users were excluded. The analyses were adjusted for sex, age, smoking, cohort, fasting glucose, serum insulin measurements,
systolic blood pressure, diastolic blood pressure, blood pressure lowering medication, cholesterol, and body mass index. AF atrial fibrillation, HR hazard ratio,
CI confidence interval
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There are no other studies addressing the relation be-
tween diabetes and thyroid function in the euthyroid
range or in individuals with prediabetes. Even though
there are many cross-sectional reports studying the preva-
lence of diabetes and thyroid dysfunction, only few have
investigated the association of thyroid function with the
occurrence of diabetes and all were register-based studies.
Our results are in contrast to a Danish nationwide registry
study by Brandt et al. [17] that reported an increased risk
of diabetes in hyperthyroid individuals, whereas we did
not find an increased risk of diabetes with higher thyroid
function. However, there are several factors that could ex-
plain these differences, including variance in the mean age
and possible iodine status of the studied population. Most
importantly, the study by Brandt et al. [17] did not include
laboratory measurements of thyroid function and there-
fore misclassification of the diagnosis of hyperthyroidism
could have occurred. Further, they did not provide es-
timates in the euthyroid range of thyroid function.
Two other register-based studies report an increased
risk of diabetes in hypothyroid individuals [18, 19] and
our results are largely in line as we find an increased
risk of diabetes in lower thyroid function.
There are several pathways that may explain the ob-
served relation between low and low-normal thyroid
function and the risk of diabetes. Overt and subclinical
hypothyroidism are associated with a decreased insulin
sensitivity and glucose tolerance, partially due to a de-
creased ability of insulin to increase glucose utilization
mainly in muscle [14, 25]. Other mechanisms, such as
downregulation of plasma membrane glucose transporters
and direct effects on insulin degradation, have also been de-
scribed [2628]. Treatment of hypothyroidism has been
shown to restore insulin sensitivity and the secretion of glu-
coregulatory hormones [15]. Furthermore, hypothyroidism
is associated with several components of the metabolic syn-
drome and could therefore indirectly relate to the increased
risk of diabetes [29]. However, in our analyses, adjusting for
several cardiovascular risk factors and components of the
metabolic syndrome did not shift risk estimates towards
the null. Additionally, excluding participants using thyroid
hormone replacement therapy at baseline only slightly
Fig. 3 The 7-year absolute risk of progression from prediabetes to type 2 diabetes is plotted against thyroid-stimulating hormone (TSH) and free
thyroxine (FT4) values within the normal range. These analyses are adjusted for sex, age, smoking, cohort, fasting serum glucose levels, fasting
serum insulin measurements, systolic blood pressure, diastolic blood pressure, blood pressure lowering medication, high-density lipoprotein
cholesterol, and body mass index
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altered the results. Even though overt hyperthyroidism is
also associated with insulin resistance, our data show that
high and high-normal thyroid function are protective
against the development of or progression to diabetes. It
could be that insulin resistance in hyperthyroid patients is
counterbalanced by other mechanisms associated with pro-
longed thyroid hormone excess, such as improved beta-cell
function and increased insulin secretion [6]. However, the
exact pathophysiological mechanisms through which
thyroid function could affect diabetes risk in the general
population remain to be determined.
The clinical importance of these findings could be sev-
eral. First of all, the association of thyroid function with
development from prediabetes to diabetes is prominent.
Thus, individuals with a low-normal thyroid function,
which includes a large proportion of the population, are
at an even higher risk of progression from prediabetes to
diabetes. Secondly, with ageing and increasingly obese
populations, there is need for better screening and pre-
vention options for diabetes [30]. One could hypothesize
that, in individuals with prediabetes with low or low-
normal thyroid function (i.e., high TSH and low FT4),
lifestyle interventions or diabetes treatment could be
prompted in an earlier phase than those with normal or
high thyroid function. Alternatively, having prediabetes
could be an argument to start treatment of subclinical
hypothyroidism to aim for prevention of overt diabetes.
Current guidelines do not recommend or specifically ad-
dress screening of thyroid function or treatment of thyroid
dysfunction in individuals with type 2 diabetes [31, 32].
The relative risk increase of developing diabetes with
thyroid function differences is modest. However, due to
the high population risk of diabetes, the implications on
the absolute risk are large. Despite this high occurrence
of both conditions in the general population, the relation
between thyroid dysfunction and diabetes had remained
largely unexplored. Further research is needed to deter-
mine to what extend the association could be driven by
thyroid hormone-related acceleration of development of
diabetes or perhaps by other mechanisms such as a
common genetic predisposition. If our results are con-
firmed, subsequent studies could focus on screening and
prevention strategies as well as questions concerning
treatment of subclinical hypothyroidism in patients at
risk for diabetes.
Strengths of our study include the large number of in-
dividuals, the variety of available confounders adjusted
for, and the long follow-up. Furthermore, we were able
to investigate both diabetes risk as well as progression
from prediabetes to diabetes. Limitations of our study
should also be acknowledged. Residual confounding cannot
be excluded in an observational study, even with the large
number of potential confounders adjusted for in our ana-
lyses. Furthermore, the Rotterdam Study is predominantly
composed of white participants aged 45 years and older
and results may therefore not be generalizable to other
populations.
Conclusions
In conclusion, our results suggest that low and low-normal
thyroid function are related to an increased risk of diabetes.
In individuals with prediabetes and low and low-normal
thyroid function, the risk of progression to diabetes seems
more prominent. Our data provide new insights into the
magnitude of the risk of diabetes and prediabetes associated
with variations of thyroid function within the normal range.
More research is needed to confirm these current findings
in various populations. Subsequent studies could address
possible screening and treatment modalities for both
diabetes and thyroid dysfunction.
Additional files
Additional file 1: Table S1. Sensitivity analyses for association between
thyroid function and risk of diabetes. (DOCX 19 kb)
Additional file 2: Table S2. Association between thyroid function in
normal range and the risk of incident diabetes in individuals with
prediabetes. (DOCX 19 kb)
Abbreviations
CI: Confidence interval; FT4: Free thyroxine; HR: Hazard ratio; RS: Rotterdam
Study; TPOAb: Thyroid peroxidase antibodies; TSH: Thyroid-stimulating
hormone
Acknowledgments
We are grateful to the study participants, the staff from the Rotterdam Study,
and participating general practitioners and pharmacists. We would also like
to thank Mr. Wichor M. Bramer from the medical library (Medical Library,
Erasmus Medical Center, Rotterdam) for the important contribution to the
literature search.
The Rotterdam Study is supported by the Erasmus MC and Erasmus
University Rotterdam; the Netherlands Organization for Scientific Research
(NWO); the Netherlands Organization for Health Research and Development
(ZonMw); the Research Institute for Diseases in the Elderly (RIDE); the
Netherlands Genomics Initiative (NGI); the Ministry of Education, Culture and
Science; the Ministry of Health Welfare and Sports; the European Commission
(DG XII); and the Municipality of Rotterdam. The funding sources had no
involvement in the collection, analysis, writing, interpretation, nor in the
decision to submit the paper for publication.
Prof. Dr. R. P. Peeters and L. Chaker are supported by a Zon-MWTOP grant
(nr 91212044) and an Erasmus MCMRACE grant. Dr. A. Dehghan is supported
by NWO grant (veni, 916.12.154) and the EUR Fellowship.
Funding
There was no funding obtained for this specific manuscript.
Authorscontributions
LC contributed to study design, collecting data, data analyses and writing of
the report. SL was involved in data analysis and writing of the report. TIMK
took part in the study design and writing of the report. AH was the principal
investigator and contributed to study design, data collection, and writing of
the report. OHF was the local principal investigator and participated in the
design and implementation of the study and the writing of the report. RPP
and AD were responsible for the overall supervision and contributed to data
analyses and writing of the report, and contributed equally to this work. All
authors had access to the data, commented on the report drafts, and
approved the final submitted version.
Chaker et al. BMC Medicine (2016) 14:150 Page 7 of 8
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Competing interests
Prof. O. H. Franco works at ErasmusAGE, a center for aging research across
the life course funded by Nestle Nutrition (Nestec Ltd.), Metagenics Inc., and
AXA. Nestle Nutrition (Nestec Ltd.), Metagenics Inc., and AXA had no role in
design and conduct of the study, collection, management, analysis, and
interpretation of the data, or in the preparation, review or approval of the
manuscript. The authors declare that they have no competing interests.
Author details
1
Rotterdam Thyroid Center, Erasmus University Medical Center, Rotterdam,
The Netherlands.
2
Department of Internal Medicine, Erasmus University
Medical Center, Rotterdam, The Netherlands.
3
Department of Epidemiology,
Erasmus University Medical Center, Room NA-2828, 3000CA Rotterdam, The
Netherlands.
4
Department of Epidemiology, Harvard T.H. Chan School of
Public Health, Boston, MA, USA.
Received: 15 March 2016 Accepted: 13 September 2016
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... Several risk factors contribute to T2DM, including age, hypertension, family history of diabetes (FHD), obesity, and sociodemographic factors (4-7); Additionally, the association between thyroid dysfunction and T2DM has also been discussed (8). The effects of hypo-and hyperthyroid dysfunctions and even thyroid hormones within the reference range and T2DM have been reported with controversial results (9,10). The underlying mechanisms and potential interactive stimuli are complex (9). ...
... The effects of hypo-and hyperthyroid dysfunctions and even thyroid hormones within the reference range and T2DM have been reported with controversial results (9,10). The underlying mechanisms and potential interactive stimuli are complex (9). Thyroid hormones unequivocally regulate glucose homeostasis through diverse mechanisms, including cellular glucose transport, intestinal glucose absorption, hepatic glucose secretion, and the secretion of insulin and counter-regulatory hormones (11). ...
... Thyroid hormones unequivocally regulate glucose homeostasis through diverse mechanisms, including cellular glucose transport, intestinal glucose absorption, hepatic glucose secretion, and the secretion of insulin and counter-regulatory hormones (11). In the Rotterdam study, each unit increase in the thyroid-stimulating hormone (TSH) level increased the risk of incidence of T2DM by 9% in euthyroid individuals (9); however, in the Health in Pomerania study, each unit increase of serum TSH decreased the risk of incidence of T2DM by 6% (12). A meta-analysis suggested that higher serum TSH or free thyroxine (FT4) levels might increase the risk of T2DM. ...
Article
Full-text available
Background Type 2 diabetes mellitus (T2DM) poses a significant public health challenge, contributing to considerable morbidity and mortality worldwide, which necessitates urgent preventive measures. Thyroid disorders, prevalent in many individuals, are intricately linked to metabolic health, yet studies on their relationship with T2DM yield inconsistent results—some suggesting an increased risk with abnormal thyroid hormone levels, while others indicate potential protective effects. This study investigated the association between changes in serum thyroid-stimulating hormone (TSH) and free thyroxine (FT4) levels and the incidence of type 2 diabetes mellitus. Methods Data from 1938 individuals aged ≥20 in the Tehran Thyroid Study cohort were used, spanning four examination cycles from 1999 to 2012, with three-year intervals. TSH and FT4 levels were log-transformed and modeled as time-varying exposures to study their association with incident T2DM. Results During a median follow-up of 9.43 years, 135 new T2DM cases were identified. The multivariable-adjusted joint model (JM) revealed that each unit increase in log-transformed TSH level was associated with a 25% decrease in T2DM incidence [HRs (95% CI): 0.75 (0.64-0.90)]. Conversely, each unit increase in FT4 level showed a marginally significant higher risk [1.06 (0.99-1.13); p-value=0.06]. Conclusion The findings of this study suggest that dynamic changes in serum thyroid hormones are associated with the development of T2DM. Rising TSH and decreasing FT4 over time are associated with a lower risk of diabetes. These findings suggest a complex interplay between thyroid function and the risk of T2DM, emphasizing the importance of monitoring thyroid hormone levels as a part of T2DM prevention strategies.
... Effects on high density lipoprotein (HDL-C) are variable, although there is usually an increase in the ratio of ApoB:ApoAcontaining lipoproteins. [56] Disturbances of multiple pathophysiological processes contribute to the effects of hypothyroidism on the lipid profile, including increased cholesterol production (e.g. via inhibition of hepatic HMG-CoA reductase and increased intestinal cholesterol [12,13] Obs Obs Increased diastolic and/or systolic BP or both for populations with OH or SCH vs. euthyroidism [14] Obs Mendelian randomisation study showed that genetically predicted low T4 predicted hypertension [15,16] Obs High TSH or low T4 predicted hypertension [17] Obs No significant association between SCH and hypertension or BP [18][19][20] MA Meta-analyses associated SCH with increased risk of hypertension of variable magnitude Dyslipidaemia [14] Obs Mendelian randomisation study showed that genetically predicted low T4 predicted dyslipidaemia [21] Obs Positive correlation between serum TSH and total-C, LDL-C and Apolipoprotein B [22] Obs The lipid profile in SCH may be more atherogenic (increased lipid peroxidation) [23] Obs No significant association of OH or SCH with dyslipidaemia after adjustment for other factors [24][25][26][27][28] MA Meta-analyses confirmed significant associations of SCH with adverse lipid profiles Impaired blood glucose control [14] Obs Mendelian randomisation study showed that genetically predicted low T4 predicted dyslipidaemia [29,30] Obs OH or SCH was associated with insulin resistance, diminished insulin secretion and increased hepatic glucose production [31,32] Obs High-normal TSH levels or low-normal T4 (within reference ranges) predicted development of type 2 diabetes or prediabetes, respectively [33,34] Obs Increased prevalence of diabetes in people with hypothyroidism [35] Obs Thyroid function was depressed in people with vs. without new-onset diabetes [36] Obs More diabetes-associated hypoglycaemia in people with vs. without thyroid disease (unspecified) ...
... Insulin resistance appears to accompany hypothyroidism [29], with diminished pancreatic insulin secretion and increased hepatic glucose production, both of which are likely to predispose the patient to the development of fasting hyperglycaemia [30]. A prospective cohort study showed that higher TSH predicted a higher risk of developing type 2 diabetes, even within the reference range for this parameter [31]. Low-normal FT4 has been shown elsewhere to predict the presence of prediabetes [32]. ...
Article
Full-text available
Background Thyroid hormones influence the function of essentially every system of the body, including the cardiovascular and metabolic system. Thyroid hormone replacement with levothyroxine (LT4) is the mainstay of pharmacological management for people with (especially clinically overt) hypothyroidism, and it is important to ensure the cardiovascular and metabolic safety of this treatment. This is especially so as in hypothyroidism, cardiometabolic risk factors and cardiovascular disease are highly prevalent conditions and will often coexist in an individual patient. Accordingly, we have reviewed the cardiometabolic consequences of hypothyroidism and intervention with thyroid hormone replacement. Main body Numerous observational studies and meta-analyses have described multiple potentially adverse cardiometabolic consequences of hypothyroidism, including exacerbation of cardiovascular and metabolic risk factors (especially dyslipidaemia), functional impairment of the heart and vasculature (including accelerated atherosclerosis) and increased risk of advanced cardiovascular outcomes. LT4 usually improves cardiometabolic risk factors in people with hypothyroidism and some (but not all) studies have reported improved vascular and cardiac function in LT4-treated populations. Observational data have suggested the possibility of improved cardiometabolic outcomes with LT4 treatment, particularly in younger people with hypothyroidism, although data from randomised, controlled trials are needed here. Importantly, LT4 (with or without additional triiodothyronine) appears to be safe from a cardiovascular perspective, as long as overtreatment and iatrogenic thyrotoxicosis are avoided. Conclusions Overall, the current evidence base supports intervention with LT4 to protect the cardiometabolic health of people with hypothyroidism who require thyroid hormone replacement, although more data on long-term clinical outcomes are needed.
... Although a shared pathogenesis involving impaired mitochondrial metabolism has been suggested, the underlying mechanisms and long-term contributing factors remain complex (Crunkhorn and Patti 2008). A longitudinal study conducted in the Netherlands with a follow-up period of 7.9 years found that individuals with hypothyroidism had a significantly higher incidence of developing T2D than those with normal thyroid function (Chaker, Ligthart et al. 2016). ...
... Notably, another large-scale meta-analysis of thyroid hormone levels, cardiovascular disease and mortality, also identified a Jshaped association between fT4 and these outcomes, which underlines the clinical importance (Xu, Derakhshan et al. 2023). In a Dutch cohort study, the risk of T2D was 1.16 times higher with elevated TSH levels and for every doubling of TSH levels the T2D prevalence increased by 1.09 times (Chaker, Ligthart et al. 2016). Furthermore, a 7-year follow-up study in euthyroid individuals revealed that fluctuations in TSH and thyroid hormones, even within the normal reference range, were an additional risk factor of the onset of T2D (Jun, Jee et al. 2017). ...
Article
Full-text available
Background: Thyroid dysfunctions, such as hypothyroidism, hyperthyroidism, are known to influence metabolism, but their long-term impact on the development of type 2 diabetes mellitus (T2D) in humans remains elusive. Thus, this study aimed to assess the cumulative incidence and association between thyroid disorders and T2D development. Methods: We conducted a retrospective cohort study using data from the Disease Analyzer database (IQVIA™) from 2005 to 2022. The study included 158,674 patients with thyroid disorder and an equal number of matched patients without thyroid disorder. Propensity score matching was performed to balance age, sex, co-diagnoses between the cohorts. Kaplan-Meier curves and Cox regression models were used to assess the cumulative incidence and hazard ratios (HR) for new-onset T2D. Results: After a 10-year follow-up period, the cumulative incidence of T2D was higher in patients with thyroid disorder compared to the non-thyroid disorder cohort (p<0.001). The HRs for T2D were 1.34 (95% CI: 1.28–1.39) for hypothyroidism and 1.30 (95% CI: 1.21–1.39) for hyperthyroidism. The strongest associations were observed in younger age groups for both hypothyroidism and hyperthyroidism. Conclusion: Thyroid disorders, including hypothyroidism and hyperthyroidism, are associated with an increased incidence of new-onset T2D. These findings suggest the need for proactive screening and management of glucose metabolism in patients with thyroid dysfunctions, particularly in younger individuals, independent of metabolic risk factors.
... https://journals.ust.edu/index.php/yjms consider the intricate relationship between these conditions (24,48). Thyroid disorders can exacerbate T2DM, and diabetes can, in turn, aggravate thyroid dysfunction. ...
Article
Full-text available
Background: Patients with type 2 diabetes mellitus (T2DM) frequently have thyroid dysfunction, an endocrine condition that requires careful examination. Objective: The prevalence of thyroid dysfunction among 100 T2DM patients was explored in this cross-sectional study. Method: Thyroid function was assessed using levels of free thyroxine (FT4), free triiodothyronine (FT3), and thyroid-stimulating hormone (TSH). Results: The findings showed a 20% prevalence of thyroid dysfunction, with hypothyroidism accounting for 18%. Notably, patients with and without thyroid disease did not differ significantly in terms of age or gender. However, patients with thyroid dysfunction had noticeably higher TSH levels (p=0.001). Conclusion: These results underscore how crucial routine thyroid function testing is for T2DM patients to promote early detection and efficient treatment.
... The variety and convenience of modern diets have led to a growing number of individuals with speci c food preferences. While the relationship between thyroid function and metabolic disorders such as type 2 diabetes has been established [17], the speci c associations between dietary unsaturated fatty acids and the risk of HT remain to be fully elucidated. This study aims to contribute to the existing body of knowledge by examining the associations of dietary intakes of unsaturated fatty acids with the prevalence of HT in a large, nationally representative sample of the U.S. population from NHANES 2007-2012. ...
Preprint
Full-text available
Purpose Hashimoto's thyroiditis (HT), a prevalent autoimmune disorder, primarily targets the thyroid gland. The influence of dietary factors, particularly unsaturated fatty acids, on HT remains underexplored. This study investigates the association between unsaturated fatty acids and HT prevalence using data from the National Health and Nutrition Examination Survey (NHANES) 2007-2012. Methods A cross-sectional study involving 6944 participants (mean age 49.73 ± 17.71 years) was conducted. Demographic, lifestyle, dietary, and urinary characteristics were assessed. Logistic regression models were employed to control for potential confounders and to estimate odds ratios (ORs) with 95% confidence intervals (CIs) for the association between unsaturated fatty acids and HT. Results The overall prevalence of HT was 11.82%. Individuals with HT were more likely to be older, female, married, non-smokers, drinkers, and have higher income. Dietary intakes of carbohydrates, sodium, energy, protein, polyunsaturated fatty acids (PUFAs), and monounsaturated fatty acids (MUFAs) were significantly lower in the HT group. Additionally, urinary cadmium concentrations were reduced in this group. After adjustments, higher intakes of PUFAs (OR 0.62, 95% CI 0.42-0.89) and a higher ratio of MUFAs to total fatty acids (OR 0.67, 95% CI 0.50-0.90) were associated with a lower risk of HT. Subgroup analyses indicated that these associations were particularly evident among females, individuals under 40 years of age, non-smokers, and alcohol consumers. A restricted cubic spline (RCS) model revealed a nonlinear relationship between PUFAs and HT (P-overall < 0.001, P-non-linear = 0.0127). Sensitivity analyses confirmed the robustness of these findings. Conclusion This study demonstrates that higher intake of unsaturated fatty acids, especially PUFAs and MUFAs, is associated with a reduced risk of HT. The identified nonlinear relationship between PUFAs and HT highlights the complex interplay of dietary factors in autoimmune thyroid diseases. Further research is warranted to elucidate the underlying mechanisms of these associations.
... In accordance with the previous literature, the thyroid hormone has been shown to augment beta-cell viability [29]. Chaker et al. [30] performed a population-based prospective cohort study and discovered that subclinical hypothyroidism is a risk factor for incident diabetes among individuals with prediabetes. Recently, a study conducted in Japan demonstrated that both hyperthyroidism and hypothyroidism correlate with type 2 diabetes, and that a population with subclinical hypothyroidism showed a higher incidence of diabetic complications [31]. ...
Article
Full-text available
Background: The prevalence of diabetes is increasing worldwide, particularly in the Pacific Ocean island nations. Although machine learning (ML) models and data mining approaches have been applied to diabetes research, there was no study utilizing ML models to predict diabetes incidence in Taiwan. We aimed to predict the onset of diabetes in order to raise health awareness, thereby promoting any necessary lifestyle modifications and help mitigate disease burden. Methods: The research dataset used in the study was retrieved from the Clinical Data Center of Taichung Veterans General Hospital. We collected data from the available electronic health records with a total of 33 items being employed for model construction. Individuals with diabetes and those with missing data were excluded. Ultimately, 6687 adults were included in the final analysis, where we implemented three different ML algorithms, including logistic regression (LR), random forest (RF) and extreme gradient boosting (XGBoost) in order to predict diabetes. Results: The top five important factors involved in the prediction model were glycated hemoglobin (HbA1c), fasting blood glucose, weight, free thyroxine (fT4), and triglycerides (TG). Notably, random forest, logistic regression, and XGBoost reached 99%, 99%, and 98% accuracy, respectively. fT4 seems to be one of the significant features in predicting the onset of diabetes. Moreover, this would be the first study using machine learning models to predict diabetes that has demonstrated the importance of thyroid hormone. Conclusions: A total of 33 items were able to be put into the machine learning model in order to predict diabetes with promising accuracy. In comparison to prior studies on machine learning models, this study not only identified similar key factors for predicting diabetes but also highlighted the significance of thyroid hormones, a factor that was previously overlooked. Moreover, it highlighted the relevance of predicting type 2 diabetes using more affordable methods, which would be useful for clinical healthcare professionals and endocrinologists who apply the models to clinical practice.
... per 1 SD increase in log TSH). [38] In some cross sectional studies raised serum TSH was associated with IR indicating that these person may develop DM in near future. [39] Chang et al. from Tiawan in a 2.6-year follow-up study found that people with elevated TSH (>5 mIU/ml) are at high risk of developing prediabetes (HR; 1.16: 95% CI: 1.05-1.28) ...
Article
Full-text available
The relationship between subclinical hypothyroidism (SCH) and type 2 diabetes mellitus (DM) is complex and controversial. Many epidemiological studies have reported a positive association; however, few have reported none. In animal models and humans, evidences suggest that hypothyroidism induces insulin resistance, beta cell dysfunction, and increased hepatic glucose production. Untreated SCH can increase the risk of diabetic complications. Beneficial effect of treatment of SCH in patients with diabetic nephropathy (DN) and retinopathy has been seen. Treatment of SCH in patients with DM should be individualized. Treatment of SCH is justified in the patients with thyroid-stimulating hormone (TSH) <10 and DN, diabetic retinopathy and patients positive for antithyroid peroxidase antibody. An algorithm for the treatment of SCH in patients with DM is also provided.
Article
Type 2 diabetes mellitus (T2DM) and thyroid dysfunction are some of the most prevalent endocrine disorders globally. Previous studies on the association and effect of thyroid hormones in patients with diabetes have yielded contradictory results. Therefore, this meta-analysis comprehensively examined the latest evidence regarding the bilateral association between thyrotropin and thyroid hormone levels in T2DM. A thorough search across multiple databases was conducted to investigate the bidirectional relationship between thyroid hormones and T2DM. Two researchers independently performed data extraction and study quality was assessed using the Newcastle–Ottawa scale, with prevalence, odds ratios, and hazard ratios calculated using a random-effects model. After screening 4159 studies, 36 were deemed eligible based on the inclusion criteria. A one-unit increase in serum thyroid-stimulating hormone (TSH) level was associated with a 2.49-fold increased odds of T2DM (OR: 2.49, 95%CI: 1.97–3.0). Similarly, a one-unit increase in Triiodothyronine (FT3) levels was associated with a 17% (HR:1.17,95%CI: 1.07–1.26) increased risk of T2DM. The pooled risk estimates of T2DM were 3.63 (95%CI: 1.63–8.09) for hypothyroidism, and 16.33 (95%CI: 7.59–35.12) for overt hypothyroidism. Individuals with thyroid dysfunction exhibited significantly higher HbA1c levels (Hedges'g: - 0.26, 95% CI: - 0.47 to - 0.06) and fasting plasma glucose (FPG) levels (Hedges'g: - 0.33, 95% CI: - 0.61 to - 0.05) compared to those with normal thyroid function. Thyroid dysfunction, including both overt and subclinical hypo- and hyperthyroidism, significantly increases the risk of T2DM. Elevated TSH and FT3 levels are linked to higher diabetes risk, highlighting the need for regular thyroid screening and integrated clinical management.
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Background Prediabetes is the earliest identifiable stage of glycemic dysregulation, and its progression can be delayed by effective control of risk factors. Currently, various risk factors for the progression from prediabetes to type 2 diabetes mellitus (T2DM) need to be further summarized. Objective This systematic evaluation of the risk factors for the progression of prediabetes to type 2 diabetes mellitus provides a theoretical basis for early recognition and intervention. The meta-analysis identifies the Fatty Liver Index as a significant risk factor [OR = 6.14, 95% CI (5.22, 7.22)] for the progression from prediabetes to type 2 diabetes, highlighting its predictive value. Methods PubMed, Web of Science, Embase, The Cochrane Library, CNKI, WANFANG, and VIP databases were searched to collect cohort studies on risk factors for progressing to type 2 diabetes in prediabetes from inception to February 15, 2024. STATA 17.0 was used for Meta-analysis. Results A total of 59 studies were included, all of which were of medium to high quality. The factors were categorized into four major groups: sociodemographic factors, lifestyle factors, psychosocial factors, and comorbidities and clinical indicators. Meta-analysis results showed that sociodemographic factors [age [OR = 1.03, 95% CI (1.01, 1.04)], family history [OR = 1.48, 95% CI (1.36, 1.61)], male sex [OR = 1.13, 95% CI (1.08, 1.19)], high BMI [OR = 1.21, 95% CI (1.15, 1.27)], high waist circumference [OR = 1.49, 95% CI (1.23, 1.79)], and high waist-to-hip ratio [OR = 2.44, 95% CI (2.17, 2.74)]]. Lifestyle factors included a lack of physical exercise [OR = 1.86, 95% CI (1.19, 2.88)], smoking [OR = 1.31, 95% CI (1.22, 1.41)], and moderate physical activity [OR = 0.24, 95% CI (0.09, 0.67)]. Psychosocial factors included anxiety [OR = 2.61, 95% CI (1.36, 5.00)], depression [OR = 1.88, 95% CI (1.35, 2.61)], and social deprivation level 4 [OR = 1.15, 95% CI (1.13, 1.18)]. Comorbidities and clinical indicators included hypertension [OR = 1.41, 95% CI (1.33, 1.50)], high triglycerides [OR = 1.25, 95% CI (1.10, 1.43)], high cholesterol [OR = 1.09, 95% CI (1.06, 1.12)], fatty liver index [OR = 6.14, 95% CI (5.22, 7.22)], low HDL-C [OR = 1.13, 95% CI (1.09, 1.36)], and high blood glucose levels [OR = 1.01, 95% CI (1.01, 1.02)]. Conclusions This study found that age, male sex, positive family history of type 2 diabetes, high BMI, unhealthy lifestyle, anxiety, depression, high blood pressure, high triglycerides, and a high fatty liver index are risk factors for the progression from prediabetes to type 2 diabetes and should be given sufficient attention. Moderate physical activity and Low HDL-C are protective factors. Future studies should also increase follow-up, explore the best diagnostic criteria for prediabetes, and fully consider the definitions of various factors. The study was registered in PROSPERO (CRD42024513931).
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The Rotterdam Study is a prospective cohort study ongoing since 1990 in the city of Rotterdam in The Netherlands. The study targets cardiovascular, endocrine, hepatic, neurological, ophthalmic, psychiatric, dermatological, otolaryngological, locomotor, and respiratory diseases. As of 2008, 14,926 subjects aged 45 years or over comprise the Rotterdam Study cohort. The findings of the Rotterdam Study have been presented in over 1200 research articles and reports (see www.erasmus-epidemiology.nl/rotterdamstudy ). This article gives the rationale of the study and its design. It also presents a summary of the major findings and an update of the objectives and methods.
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Context: Associationsbetweenautoimmunediabetesandautoimmunethyroid disease areknown, but insufficiently characterized. Some evidence suggests that type 2 diabetes may also be associated with hypothyroidism. Objective: To investigate associations of autoimmune and type 2 diabetes with the prevalence of hypo- and hyperthyroidism. Design and setting: Cross-sectional population-based study of adults in two surveys of the HUNT Study. Participants: A total of 34,235 participants of HUNT2 (1995-97) and 48,809 participants of HUNT3 (2006-08). Main outcome measures: Prevalence of hypo- and hyperthyroidism, assessed by self-report, serum measurements and linkage with the Norwegian Prescription Database. Results: In HUNT2, autoimmune diabetes was associated with a higher age-adjusted prevalence of hypothyroidism among both women (prevalence ratio [PR] 1.79, 95% confidence interval [CI] 1.30-2.47) and men (PR 2.71, 95% CI 1.76-4.19), compared with having no diabetes. For hyperthyroidism, the corresponding cumulative prevalence ratios were 2.12 (95% CI 1.36-3.32) in women and 2.54 (95% CI 1.24-5.18) in men with autoimmune diabetes. The age-adjusted excess prevalence of hypothyroidism (~6 percentage points) and presence of thyroid peroxidase antibodies (TPOAb; 8-10 percentage points) associated with autoimmune diabetes was similar in women and men. Type 2 diabetes was not associated with the prevalence of hypothyroidism. In HUNT3, associations were broadly similar to those in HUNT2. Conclusions: Autoimmune diabetes, but not type 2 diabetes, was strongly and gender-neutrally associated with increased prevalence of hypo- and hyperthyroidism and presence of TPOAb. Increased surveillance for hypothyroidism appears not necessary in patients with type 2 diabetes.
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Context Hyperthyroidism is an established risk factor for atrial fibrillation (AF), but information concerning the association with variations within the normal range of thyroid function and subgroups at risk is lacking. To investigate the association between normal thyroid function and AF prospectively and explore potential differential risk patterns. From the Rotterdam Study we included 9166 participants ≥45 years with thyroid stimulating hormone (TSH) and/or free thyroxine (FT4) measurements and AF assessment (1997-2012, median follow-up 6.8 years), with 399 prevalent and 403 incident AF cases. Outcome measures were threefold 1) Hazard Ratio's (HRs) for the risk of incident AF by Cox Proportional-Hazards models 2) Ten-year absolute risks taking competing risk of death into account. 3) Discrimination ability of adding FT4 to the CHARGE-AF Simple Model, an established prediction model for AF. Higher FT4 levels were associated with higher risks of AF (HR 1.63, 95% Confidence Interval 1.19-2.22), when comparing those in the highest quartile to those in lowest quartile. Absolute 10-year risks increased with higher FT4 in participants ≤65 years from 1% to 9% and from 6% to 12% in subjects ≥65 years. Discrimination of the prediction model improved when adding FT4 to the Simple Model (c-statistic 0.722 vs 0.729, p=0.039). TSH levels were not associated with AF. There is an increased risk of AF with higher FT4 levels within the normal range, especially in younger subjects. Adding FT4 to the Simple Model slightly improved discrimination of risk prediction.
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To identify risk factors for the development of statin-associated diabetes mellitus (DM). The study was conducted in two phases. Phase one involved high-throughput in silico processing of a large amount of biomedical data to identify risk factors for the development of statin-associated DM. In phase two, the most prominent risk factor identified was confirmed in an observational cohort study at Clalit, the largest health-care organization in Israel. Time-dependent Poisson regression multivariable models were performed to assess rate ratios (RRs) with 95% CIs for DM occurrence. A total of 39,263 statin nonusers were matched by propensity score to 20,334 highly compliant statin initiators in 2004-2005 and followed until the end of 2010. Within 59,597 statin users and nonusers in a multivariable model, hypothyroidism and subclinical hypothyroidism carried an increased risk for DM (RR 1.53 [95% CI 1.31-1.79] and 1.75 [1.40-2.18], respectively). Hypothyroidism increased DM risk irrespective of statin treatment (RR 2.06 [1.42-2.99] and 1.66 [1.05-2.64] in statin users and nonusers, respectively). Subclinical hypothyroidism risk for DM was prominent only upon statin use (RR 1.94 [1.13-3.34] and 1.20 [0.52-2.75] in statin users and nonusers, respectively). Patients with hypothyroidism treated with thyroid hormone replacement therapy were not at increased risk for DM. Hypothyroidism is a risk factor for DM. Subclinical hypothyroidism-associated risk for DM is prominent only upon statin use. Identifying and treating hypothyroidism and subclinical hypothyroidism might reduce DM risk. Future clinical studies are needed to confirm the findings. © 2015 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.