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93
Hellenic Journal of Nuclear Medicine January-April 2017
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Michael I. Liontiris, MD,
Elias E. Mazokopakis MD, PhD
Department of Internal Medicine,
Naval Hospital of Crete, Chania,
Greece
Keywords: Hashimoto's thyroiditis
Diet - Iodine - Selenium - Vitamin-D
- Gluten - Autoimmunity
- Clinical course
Corresponding author:
K. Mitsotaki 36, Chania,
73 132, Crete, Greece.
Tel.: (+30) 2821 0 82754,
Fax: (+30) 2821 0 82510.
emazokopakis@yahoo.gr
Receved:
10 January 2017
Accepted revised :
27 February 2017
A concise review of Hashimoto thyroiditis (HT) and
the importance of iodine, selenium, vitamin D and
gluten on the autoimmunity and dietary management
of HT patients.Points that need more investigation
Abstract
Hashimoto's thyroiditis (HT) is a chronic autoimmune thyroid disease caused by an interaction between ge-
netic factors and environmental conditions, both of which are yet to be fully understood. The management
of HT depends on its clinical manifestations, commonly including diuse or nodular goiter with euthyro-
idism, subclinical hypothyroidism and permanent hypothyroidism. However, in most cases of patients with
HT, lifelong levothyroxine substitution is required. The additional role of diet for the management of HT is
usually overlooked. A literature search regarding the importance and the inuence of iodine, selenium, vita-
min D and gluten on HT was conducted. In HT careful supplementation of possible deciencies is recom-
mended for the dietary management of these patients. The use of a diet low in gluten among HT patients
with or without celiac disease (CD) is discussed.
Hell J Nucl Med 2017; 20(1): 51-56 Epub ahead of print: 20 March 2017 Published online: 20 April 2017
Introduction
Hashimoto's thyroiditis (HT), also called chronic lymphocytic or autoimmune thy-
roiditis (AITD), is part of the spectrum of chronic autoimmune thyroid diseases
and is associated with various degrees of thyroid hypofunction, with thyroid au-
toantibodies production like the most common, thyroid peroxidase antibodies (TPO-Ab)
and thyroglobulin antibodies (Tg-Ab)], and with lymphocytic inltration [1-5]. Its preva-
lence depends on age (more frequently appears between 45-55 years), gender (4-10 ti-
mes more frequent in females than in males) and race (more common in whites than in
blacks, hispanics and asians) [3, 6, 7]. Aside from smoking, which decreases the risk for HT,
other factors like alcohol, stress, pregnancy and drug use e.g. iodine, interferon-, immu-
nomodulatory agents such as ipilimumab, pembrolizumab, nivolumab, and the huma-
nised monoclonal antibody to CD52 alemtuzumab may in genetically predisposed indi-
viduals, initiate the development of HT [8, 9]. Although the exact mechanism of prog-
ressive thyroid tissue destruction is not clear, HT is regarded as a disorder of T cell-medi-
ated immunity, caused by an interaction between susceptibility genes and environ-men-
tal factors, the research of which is still inconclusive [5]. In most cases of patients with HT,
lifelong levothyroxine (LT4) substitution, adjusting the dose to achieve normal circu-
lating thyrotropin ( TSH) levels, is required [4, 9, 10]. In addition, the coexistence of HT
with other organ specic diseases [e.g. pernicious anemia, vitiligo, celiac disease (CD), ty-
pe 1 diabetes mellitus, autoimmune liver disease, primary biliary cirrhosis, myasthenia
gravis, alopecia areata, sclerosis multiplex, Addison's disease], and non-specic [e.g. rhe-
umatoid arthritis (RA), systemic lupus erythematosus (SLE), Sjögren syndrome, systemic
sclerosis, mixed connective tissue disease], non-endocrine autoimmune diseases should
be evaluated [11, 12]. Nuclear medicine contributes to the diagnosis of HT and hypothy-
roidism and to dierential diagnosis of HT with other diseases. Many of the tests for the
evaluation of thyroid gland function and structure and for other diseases coexisting with
HT are nuclear medicine tests.
The purpose of this article was to present an update about HT and the impor-tance of
iodine, selenium (Se), vitamin D and gluten in autoimmunity of HT and also the role of
diet in the clinical course of HT.
51
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Hashimoto's thyroiditis and iodine
Iodine is an essential micronutrient of the diet required for
thyroid function and synthesis of thyroid hormones [13].
The recommended adult daily iodine intake is 150g, inc-
reasing to 250g in pregnancy and lactation [14]. Main diet
iodine sources are seafood (e.g. seaweed, scallops, cod, sar-
dines, shrimps, salmon and tuna), animal products (yoghurt,
cow's milk, eggs) and fruits (cranberries and strawberries).
Iodine deciency causes several consequences and mani-
fests with a wide clinical range: from goiter to cretinism [15].
he problem of iodine deciency in many countries world-
wide was solved with iodized salt (IS) programs, and nowa-
days about two thirds of the world's population (71%) uses IS
[16]. In iodine-replete areas, most persons with thyroid di-
sorders have AITD ranging from primary atrophic hypothy-
roidism, HT to thyrotoxicosis caused by Graves' disease [17].
Other studies revealed the inuence of dietary iodine intake
on the epidemiology of thyroid dysfunction [17]. Studies on
the incidence of AITD have only been conducted in a small
number of developed countries. Autoimmune hypothyro-
idism and thyroid antibodies (TAb) are more common in iodi-
ne replete areas than in iodine decient areas [8, 18]. Hypo-
thyroidism induced by iodine in AITD may be due to a persis-
tent inhibitory eect of iodine on thyroid hormone synthesis
and secretion, i.e., a pathologically persistent Wol-Chaiko
eect [9, 19]. Cases of HT may have inadequate thyroid hor-
mone synthesis, may be unable to escape from the acute Wo-
lf Chaiko eect, and can develop iodine-induced hypothy-
roidism. A number of studies indicated that moderate or mild
iodine excess (median urinary iodine 220µg per 24 hours)
is associated with a more frequent occurrence of hypothy-
roidism, especially in elderly subjects, the exact mechanism
of which has not been claried [20]. In the longitudinal, po-
pulation-based DanThyr study [21] subjects were examined
at baseline in 1997 to 1998 and re-examined 11 years later in
2008 to 2010 after initiation of a mandatory programme of
salt iodization. Even small dierences in the level of iodine in-
take between otherwise com-parable populations were as-
sociated with considerable dierences in serum TSH at the
eleventh year of follow-up [21]. Furthermore, a cross-sec-
tional study from south China showed that high iodine intake
was likely to lead to the occurrence of thyroid diseases, such
as HT, nodular goiter, and hyperthyroidism, through a long-
term process [22].
Even small increases in iodine intake are associated with
an increased prevalence of thyroid autoimmunity [15]. Pe-
dersen et al. [23] found an increased prevalence of TAb, 4-5
years after a cautious salt iodization programme, suppor-
ting the view that even a small increase in iodine supple-
mentation may be associated with increased thyroid auto-
immunity. The underlying mechanism for this association is
yet to be elucidated. A recent study [24] suggested that the
apoptosis of thyroid follicular cells seen in HT development
is likely caused by suppression of autophagy activity, which
is induced by iodine excess. This process is mediated thro-
ugh transforming growth factor-1 downregulation, activa-
tion of the Akt/mTOR signaling pathway and enhanced
reactive oxygen species (ROS) production. Another poten-
tial mechanism could be that iodine excess increases intra-
thyroid inltrating Th17 cells and inhibits T regulatory ( TR-
EG) cells development, while it triggers an abnormal expres-
sion of tumor necrosis factor related apoptosis-inducing li-
gand (TRAIL) in thyrocytes, thus inducing apoptosis and pa-
renchymal destruction [25]. The fact that excessive iodine
plays a signicant role in inducing thyroid autoimmunity is
also strongly supported in genetically predisposed animals
by increasing the immunogenicity of thyroglobulin (TG)
[26]. This phenomenon may be explained by the fact that TG
is the only self-antigen that undergoes post-translational
modication as a consequence of the environmental supply
of iodine, with the exposure of previously hidden epitopes
[27-31].
Considering the above, high iodine supplementation in
HT should be discouraged, as not benecial and possibly
harmful. Discouraging iodine over-supplementation must
not preclude its appropriate supplementation in pregnancy
to a total intake of 250g/day [9].
Hashimoto's thyroiditis and selenium
Selenium (Se) is an essential micronutrient of diet with many
pleiotropic eects ranging from antioxidant and anti-inam-
matory to increasing active thyroid hormone production [32-
36]. The thyroid is the organ with the highest Se content per
gram of tissue. Among at least 30 selenoproteins, the seleno-
enzymes such as glutathione peroxidases (GPX), thioredoxin
reductases (TR), iodothyronine deiodinases and seleno-
protein P, seem to play a unique role in human thyroid func-
tion and thyroid hormone homeostasis [2, 32, 33]. Selenium
supplementation in patients with AITD, including HT, seems
to modify the inammatory and immune responses, probably
by enhancing plasma GPX and TR activity and by decreasing
toxic concentrations of hydrogen peroxide (H2O2) and lipid
hydroperoxides, resulting from thyroid hormone synthesis [2,
33, 34]. When Se intake is adequate, the intracellular GPX and
TR systems protect thyrocyte from these peroxides, as oxida-
tive stress induces TR1 and GPX [4]. This article points out that
type 1 and 2 iodothyronine deiodinases (D1 and D2) which
support the conversion of peripheral T4 to T3 via outer (5')-
ring deiodination of the pro-hormone T4, are selenoproteins
and thus this conversion is susceptible to Se deciency [37].
For that reason Se-decient individuals have mildly elevated
serum T4 and T4 to T3 ratios, but normal TSH [37].
Selenium is present in soil and enters the food chain thro-
ugh plants. So, the Secontent of plants and animals depends
on whether the soil where plants grow is seleniferous or not;
therefore the amount of Se in the soil is vital. The current re-
commended dietary intake of Se in adults, in order to achi-
eve the maximal activity of GPX in plasma or in erythrocytes
is between 55 and 75g per day [2, 38-40]. Foods rich in Se
are Brazil nuts [40], oysters, tuna, whole-wheat bread, sun-
ower seeds, most kinds of meat (pork, beef, lamb, turkey,
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chicken), mushrooms and rye. In a study conducted in the
north-west part of Greece the total daily average intake of Se
from the food was 39.3g per person [41].
Studies have shown dierent results regarding the e-
cacy of Se supplementation in HT patients [42-45]. Three
meta-analyses have conrmed a suppressive eect of Se sup-
plementationon serum TPO-Ab and Tg-Ab levels in HT pati-
ents [42-44]. Particularly, the recently (2016) published sys-
tematic review and meta-analysis of Wichman et al. (2016)
[44] showed that Se supplementation eectively reduces se-
rum TPO-Ab levels at 3, 6, and 12 months and serum Tg-Ab at
12 months in LT4-treated populations, but not in non treated
ones. However, no signicant correlation between the base-
line serum Se and the decrease in serum TPO-Ab level was
demonstrated in LT4-treated patients. This meta-analysis also
showed a signicant decrease in serum TPO-Ab levels in the
patients groups receiving 200g selenomethionine, but not
in those receiving 200g sodium selenite. The dierence
might lie on the fact that the absorption of selenite is appro-
ximately two-thirds of the absorption of selenomethionine
[3, 44]. However, another meta-analysis in the Cochrane lib-
rary concluded that the evidence to support or refute the ef-
cacy of Se supplementation in patients with HT is insuf-
cient [45].
Inhomogeneity in various groups studied, like dierences
in the duration of illness, variations in baseline serum Se and/
or iodine, the duration of the study and the dierent Se com-
pounds applied appear to play a role in the divergence of the
results [44, 46]. A most recent study from south Italy showed
that the 6 months long supplementation with L-seleno-
methionine had no eect on TPO-Ab [47]. Other Italian [48]
and a Greek [2] studies have shown that a 12 months long Se
supplementation decreased TPO-Ab. The Greek study also
showed that the patients group after ceased receiving Se,
after 6 months had a 4.8% increase in the mean serum TPO-
Ab concentrations. recent population-based study in Chi-
na [49] provided us with potent circumstantial evidence that
low Se intake is associated with thyroid autoimmunity be-
cause showed that the prevalence of thyroid diseases (ex-
cept hyperthyroidism, Graves' and nodular disease) was hig-
her in a region of low Se intake (serum Se < 69g/L) compa-
red to a region of adequate Se intake (serum Se 69g/L) [49].
Previous evidence about the relationship between Se sup-
plementation and type 2 diabetes mellitus (T2DM) has been
conicting [50-54]. In a meta-analysis of ve studies (13.460
participants) a signicantly higher prevalence of T2DM was
conrmed in patients with relatively low (97.5g/L) or high
serum Se levels (132.50g/L), revealing a U-shaped non-
linear dose-response relationship between serum selenium
and T2DM [53]. Jablonska et al. (2016) demonstrated that in
76 non-diabetics, daily supplementation with 200g Se in
the form of Se yeast for 6 weeks was associated with a signi-
cantly decreased level of HbA1c and hardly aected fasting
plasma glucose or down-regulation of seven genes involved
in dierent steps of glucose metabolism (INSR, ADIPOR1,
LDH, PDHA, PDHB, MYC, HIF1 inhibitor) [55]. Decreased ex-
pression of mRNA levels for these receptors has been linked
to insulin resistance and diabetes in humans and animals
[56-58].
Chronic ingestion of large quantities of Se may have ad-
verse eects in human health [59-64]. Consumption of ap-
proximately 330g of Se per day could be toxic not only for
growth hormones and insulin-like growth factor 1 meta-
bolism but also in the synthesis of thyroid hormones [59, 60].
Possible major side eects include nail and hair loss, ano-
rexia, diarrhea, depression, hemorrhage, liver and kidney
necrosis, blindness, ataxia and respiratory disturbances [60,
61]. There have also been instances of dermatitis and CNS
disorders in an area with high Se content in Enshi, China [62].
These signs and symptoms of Se toxicity are known as sele-
nosis. A Se intake of 50-400g/d is considered a safe range
for adults, while 850-900g could be allowed as minimum
for Se toxicity [65]. In case of Se deciency, the excessive
amounts of HO generated lead to immoderate production
of T4 and damage of thyroid cells. Selenium deciency also
increases the weight of the thyroid [66] and, combined with
iodine deciency, may lead to a further increase of thyroidal
weight. In addition, a phenomenon that has not been stu-
died with sucient experimental data is that Se deciency
causes accelerated iodine depletion [67]. This may be a pro-
tective adaptation against thyroid damage, when Se is de-
cient and iodine is adequate. Supplementing an HT patient
who is decient in both elements with either Se or iodine
would be ineective and, in certain cases, could cause com-
plications. This explains the deterioration of thyroid function
which was observed after Se administration to iodine-de-
cient people in northern Zaire, a region of endemic goiter,
suggesting that the reduction in D1 activity during Se de-
ciency might be protective against iodine deciency, presu-
mably by reducing the deiodination of T4, T3, or T3 sulfate
[37, 68, 69]. In order to predict whether a patient with HT wo-
uld benet from Se supplementation, the clinician should
rst investigate the patient's iodine status [59]. This is pos-
sible by determining the urinary iodine excretion (UIE) test
in a 24h urine collection. It should be noted that excessive
iodine may indicate dietary excess intake [70], recent con-
trast media exposure or use of drugs containing iodine (e.g.
amiodarone). The eect of iodine-containing antiseptic so-
lutions suggested by healthcare professionals appears to be
negligible [71, 72].
In summary, Se supplementation in the form of selenome-
thionine would be benecial in HT patients with Se deci-
ency and adequate iodine intake. Careful Se supplemen-
tation is required among HT patients with T2DM, but chroni-
c ingestion of large quantities of Se may have adverse eects
in human health.
Hashimoto's thyroiditis and vitamin D
Despite the fact that it was initially described as a vitamin'',
vitamin D is now considered as both a fat-soluble vitamin
and a steroid hormone that plays a central role in the regu-
lation of calcium/phosphate homeostasis and bone inten-
sity [73]. It is synthesized within the body via two routes: skin
exposure to sunlight and dietary intake [5]. The natural sour-
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ces that provide humans with large amounts of vitamin D3
are sh (cod liver oil, wild fresh salmon, sardines) and dairy
products [5]. Its serum normal range is between 30 and 80ng
/mL and levels below 30ng/mL are considered by most scho-
lars indicative of vitamin D insuciency [5].
Several studies have shown the correlation between vita-
min D deciency and thyroid autoimmunity [5, 74-78], such
as the fact that this association applies for all ages [75, 76]
and that cholecalciferol supplements are eective in redu-
cing TPO-Ab among HT patients with vitamin D deciency
[78, 79]. What is still unclear, however, is whether the low
25[OH ]D levels observed in HT patients are the result of the
disease itself or actually part of its cause. Aside from its cal-
cium/phosphate homeostasis functions, vitamin D is con-
sidered to be one of the natural immune modulators and a
regulator of various immune-mediated processes [5]. The
mechanisms underlying the assumption that vitamin D is
linked with autoimmunity are not clear but are probably as-
sociated with its anti-inammatory and immunomodu-
latory functions. The Endocrine Society of USA guidelines
armed that daily vitamin D intakes of 1500-2000IU are ne-
eded to raise the blood level of 25(OH) D constantly above
30ng/mL [80], whilst the Institute of Medicine of USA
reported that the tolerable upper intake level, dened as the
maximum daily intake above which the potential for adverse
health eects may increase after chronic use, is 4000IU per
day [81]. Levels of 25(OH) D between 30 and 40ng/mL, that
are adequate for avoiding metabolic and autoimmune di-
sorders [82], in more than 97% of the population, can be ac-
hieved by an optimal dosage of approximately 2000IU cho-
lecalciferol daily, regardless of increased exposure to UVB
[83]. The main side eect of vitamin D overtreatment is hy-
percalcemia (calcium serum levels above 11mg/dL) and
nephrolithiasis. To avoid coronary artery calcication, which
is an important predictor of cardiovascular disease (CVD),
concomitant use of cholecalciferol with vitamin K2 (mena-
quinones) may be necessary [84]. Patients with renal disease
cannot convert 25[OH]D to active 1,25[OH]D2 and need to
receive calcitriol instead of cholecalciferol. In addition, we
must consider the potential interactions of some drugs with
vitamin D supplements [5, 85]. Apart from cholecalciferol or
calcitriol, a regular exposure to sunlight could contribute to
the prevention and management of vitamin D deciency in
HT patients. It is obvious that excessive sun exposure and
sunburn should be avoided because of the high risk of skin
cancer (particularly melanoma) [86].
In summary, the presented data demonstrate the asso-
ciation of vitamin D deciency with HT pathogenesis, thy-
roid hypofunction and autoimmunity in general. Taking into
consideration the low cost and the minimal side eects of
vitamin D supplementation, screening for vitamin D de-
ciency and careful vitamin D supplementation with monthly
monitoring calcium and 25[OH]D levels, when required, may
be recommended for patients with HT [5, 73].
Hashimoto's thyroiditis and gluten
Celiac disease (CD) is an immune-mediated disease charac-
terized by chronic inammation and destruction of the vil-
lous structure of the small intestine [87, 88]. It is triggered by
the ingestion of gluten, a protein complex found in wheat
and related grains, such as barley, rye and oat. Celiac disease
has increasingly become considered as a multi-organ disor-
der, often presenting with diarrhea, malabsorption synd-
rome and weight loss, and has been linked to a number of
diseases including autoimmune disorders [87-90].
According to the international medical bibliography, AI-
TD and CD are clearly associated [12, 90-92]. This might be
explained partly by the increased immunosensitivity of CD
patients, as part of an autoimmune polyglandular synd-
rome (APS), by the deciency of key elements such as Se and
iodine due to malabsorption [93, 94] or due to antibodies
that aect both target-tissues [95]. According to a most re-
cent meta-analysis, all patients with AITD should be scre-
ened for CD, given the increased prevalence of the coexis-
tence of these two disorders [96]. This study advocates that
patients with HT must undergo celiac serological tests [se-
rum IgA and IgG gliadin antibodies (AGA-IgA, AGA-IgG), IgA
transglutaminase antibodies (TGA), and serum IgA endo-
mysium antibodies (EMA)], and that if any of the celiac sero-
logical tests is positive, the patients must be investigated
with gastroduodenoscopy and duodenal biopsy [96]. It
must be considered that positive thyroid and celiac tests
might represent an epiphenomenon, because serum auto-
antibodies generally do not reect per se a clinical autoim-
mune disease [97].
In summary, whereas it is not yet clear whether a gluten-
free diet can prevent autoimmune diseases, it is worth men-
tioning that HT patients with or without CD benet from a
diet low in gluten as far as the progression and the potential
disease complications are concerned [98]. Still, a lifelong
gluten-free diet is not easy to maintain, it could be very cos-
tly and the subject's quality of life may deteriorate [99].
In conclusion, present evidence indicates the benecial
role of diet in the autoimmune status and the clinical course
of HT patients. Serum levels of iodine, Se and vitamin D, in
HT patients are necessary, and a careful supplementation in
case of deciency of these agents is recommended. Due to
the increasing coexistence of HT with CD and other autoim-
mune diseases, a low gluten diet is important.
The authors declare that they have no conicts of interest
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