Annals of Hepatology 8(1) 2009: S44-S50
Annals of Hepatology 2009; 8(1): Supplement: S44-S50
Association between type two diabetes and
non-alcoholic fatty liver disease in youth
Anna Alisi;1 Melania Manco;2 Nadia Panera;1 Valerio Nobili1
Bambino Gesù Paediatric Hospital and Research Institute;
Type two diabetes mellitus (T2DM), metabolic syndrome (MetS),
non-alcoholic fatty liver disease (NAFLD), nonalcoholic
steatohepatitis (NASH), impaired fasting glucose (IFG), impaired
glucose tolerance (IGT), National Health and Nutrition
Examination Survey (NHANES), alanine aminotransferases
(ALT), aspartate aminotransferase (AST), free fatty acid (FFA),
Address for correspondence:
Anna Alisi, PHD
Unit of Hepatology
Bambino Gesù Hospital and Research Institute
Piazza San Onofrio 4
00165 Rome; Italy
Phone: +39-06-68592650; Fax: +39-06-68592904;
Manuscript received and accepted: 23 December 2008
In the last three decades prevalence of insulin related
diseases has been growing worldwide with epidemic
obesity, type 2 diabetes mellitus and non alcoholic fatty
liver disease. In children such epidemics are particu-
larly worrisome, since metabolic abnormalities track
to the adulthood with significant implications for the
health care system. Epidemiological studies support a
close association between type 2 diabetes and fatty liver
disease. We review the most recent epidemiological
data on prevalence of both diseases in youth and their
Key words: Aminotransferases, glucose, insulin resis-
tance, non alcoholic steatohepatitis, obesity.
Estimates from population- and hospital-based studies
indicate that the number of children and adolescents with
type two diabetes mellitus (T2DM) has been increasing
in the last decades.1 This is likely to occur since the num-
ber of adolescents and young adults affected by insulin
resistance-associated morbidities is increasing.2 In fact,
T2DM is characterized by the simultaneous occurrence
of both insulin-resistance and relative insulin-deficien-
cy.3 During puberty, insulin resistance represents a phys-
iological condition aimed to favor growth. Obesity may
exacerbate this condition. It has been shown that up to
one in third obese adolescents with insulin resistance
will keep this condition until the adulthood, whilst the
remaining two will recover normal insulin sensitivity as
it happens for all the normal weight adolescents.4 Sub-
jects with severe insulin resistance which persists over
the puberty are candidate to develop type 2 diabetes mel-
litus, when their beta cell activity fails to compensate for
increased and long term insulin resistance.5
T2DM in youth is usually not an isolated condition,
but it is often accompanied by other metabolic abnor-
malities which represent cardiovascular risk factors and
cluster together in the metabolic syndrome (MetS),6 i.e.
obesity, dyslipidemia, hypertension and low-grade in-
flammation.2,7 Recent evidence suggests a close associa-
tion also between T2DM and two other condition of in-
sulin resistance, namely the polycystic ovary syndrome
and the non-alcoholic fatty liver disease (NAFLD).8,9
NAFLD has a broad spectrum of manifestations, rang-
ing from simple steatosis to its inflammatory representa-
tion of nonalcoholic steatohepatitis (NASH). The bound-
aries between NAFLD and NASH are defined only by liv-
er biopsy and prediction is difficult using any single or
combined clinical or laboratory test.10 A small proportion
of patients with NAFLD progresses to cirrhosis, hepato-
cellular carcinoma and liver failure.11,12
Pediatric NAFLD is becoming the leading cause for re-
ferral to liver clinics especially in overweigh/obese chil-
dren from Western country.13 The occurrence of NAFLD in
these children who are already at cardiovascular risk, is
particularly worrisome, since the disease appears to be a
per se independent cardiovascular risk.9 Patients with
NAFLD seem also prone to develop more frequently an
impairment of the carbohydrate metabolism varying from
a condition of pre-diabetes to overt T2DM. In our series of
children and adolescents with biopsy proven NAFLD, we
observed a prevalence of pre-diabetes and diabetes as high
as 10-12%,14,15 and, in most of them the impaired glucose
metabolism will likely track to the adulthood.
The meaning of this association remains unclear. The
question is whether NAFLD is per sè a determinant of di-
A Alisi et al. NAFLD and T2DM
abetes or its effect is mediated by more severe obesity
and insulin resistance.
In the present review, we will try to verify the occur-
rence of this association in youth by resuming the most
recent epidemiological data on prevalence/incidence of
both diseases, thus highlighting their common trends;
and considering pathogenetic mechanisms which may
underlie both. The epidemic of T2DM and NAFLD will
bear fruit in forthcoming decades, putting further stress
on the healthcare system and, probably, leading to in-
creased morbidity and a shorter lifespan for future gener-
Epidemiology of T2DM
Prediabetes and T2DM are serious adverse conse-
quences of obesity and pediatric metabolic syndrome,
more likely to manifest in adolescence and early adult-
hood than clinical atherosclerotic diseases.16
The American Diabetes Association defines diabetes
as occurring if one of three criteria are present: 1) a casual
plasma glucose of > 200 mg/dL in some one with symp-
toms of diabetes; fasting plasma glucose of ≥ 126 mg/
dL; 3) 2 hr plasma glucose of ≥ 200 as part of an oral
glucose tolerance test.17 The dose of glucose used as load
is of 1.75 g/kg to a maximum of 75 g, although the pre-
cise pediatric dose is not well validated.18 Impaired fast-
ing glucose (IFG) or impaired glucose tolerance (IGT)
Most data on the epidemiology of diabetes comes
from national surveys. However, they provide data on in-
cidence and prevalence of the disease based on the num-
ber of cases referred by physicians or self reported by pa-
tients. For instance, the Search for diabetes in Youth is a
6-center observational study conducting population-
based ascertainment of physician diagnosed diabetes in
youth.20 The National Health and Nutrition Examination
Survey (NHANES) is a stratified, multistage probability
sample of the civilian non-institutionalized US popula-
tion and diagnosis of diabetes was self reported. To esti-
mate prevalence and incidence of diabetes, the adoles-
cents of the NHANES study (N = 4,370, age 12-19 years)
were simply asked about having or not the disease. Then,
they underwent measurement of fasting glucose. Subjects
without self reported diabetes but presenting with IFG (N
= 1,496) were considered diabetic as well.21 In a longitu-
dinal study, performed in the United Kingdom to evalu-
ate the incidence of T2DM in subjects < 17 years of age,
the estimate of cases was based on active monthly report-
ing of cases by consultant pediatricians, as described
above.22 Therefore, the major limit of this survey studies
is related to the fact that they do not estimate the rate of
prediabetes assessed by the impaired glucose tolerance,
which is, on the contrary the most frequent form of im-
pairment in the carbohydrate metabolism in the youth.
Therefore, large surveys such as the SEARCH and the
NHANES are likely to see just the top of the iceberg, and
to severely underestimate a more common phenomenon.
On the other hand, surveys offer the opportunity to evalu-
ate the effect of several factors, mainly age, sex and races.
Both prevalence and incidence of T2DM vary among
races, with the highest prevalence and incidence in mi-
norities.20-22 The SEARCH found that overall prevalence
ranged from 6% in non Hispanic white youth to 76% in
American Indians; incidence from 17 in Hispanic to 49.9
in American-Indian per x 100,000-1 x year-1 in 15-19 year
olds. In the same range of age, incidence for non-Hispan-
ic white was 5.6.20 Data from NHANES found an inci-
dence of 8.1 x 100,000-1 in 10–14-year-olds and 11.8 x
100,000-1 in 15–19-year-olds in 2002–2003. The esti-
mated incidence of T2DM in the Bostonian Youth varies
from 0.79 x 1000-1 in children ≤ 9 years of age to 1.74 x
1000-1 in adolescents (age 10-19 years).23 In the UK
study, a total of 168 confirmed cases of non-type 1 diabe-
tes were reported, resulting in a national incidence of 1.3
x 100,000-1 x year-1. Of these, 40% were diagnosed with
type 2 diabetes giving a minimum incidence of 0.53 x
100,000-1 x year-1.22 In New Zeeland, a 6 year study,
which included 1,095.074 children of ≤ 14 years old es-
timated incidence of impaired glucose tolerance (IGT)
was 0.72 x100000-1 x year-1 in subjects of ≤ 14 years
and 2.27 x100000-1 in those of 10-14 years. Type 2 DM
had a rate of 0.84 x 100,000-1 x year-1.24 In Chinese
youth, a nationally representative cross-sectional survey
enrolling 44 880 children aged 7–17.9 years, showed an
incidence of diseases, varying from 0.2 in subjects 7-12
year old to 0.4 in 12-18 year olds.25
To obtain data on rates of IGT we have to look to small
size studies, often performed in high risk populations, i.e.
including obese individuals with co-morbidities and/or fa-
miliar history of diabetes. We resume in Table 1 the most
significant among those conducted and published in the
last 5 years, and using the oral glucose tolerance test to di-
agnose diabetes.26-36 Of note, even in samples of individu-
als with severe obesity and familiarity for diabetes and car-
diovascular disease, European rates were not as high as
those in US studies. In Europe, T2DM remains a rarity, ac-
counting only for 1% to 2% of all cases of diabetes melli-
tus. Although, differences in obesity rates between US and
European youth are likely contributors, the full explana-
tion for this discrepancies remains uncertain.
Epidemiology of NAFLD
The real prevalence of NAFLD/NASH remains un-
known in the general population because prospective
studies lack and the information available in a given
population strictly depend on the diagnostic criteria
used.37 NAFLD, as estimated on the basis of ultrasonogra-
phy and increased levels of liver enzymes, seems to be
very common, occurring in persons of all ages and ethnic
Annals of Hepatology 8(1) 2009: S44-S50
Population-based studies suggest that, as in the
adults, its prevalence has been increasing over the past
three decades also in children and adolescents, and that
the disease represents a worldwide problem with case se-
ries described in North and South America, Europe, Aus-
tralia and Asia.13,37 These studies indicate that prevalence
increases with age, ranging from 0.7% for ages 2 to 4 up
to 17.3% for ages 15 to 19 years, but these rates are likely
to be underestimated and all these reports do not dis-
criminate between simple steatosis, necro-inflammation
The most prominent risk factor for fatty liver is obesi-
ty and the disease is most common in males adoles-
cents.39-41 In a recent study on 909 Korean obese children
(boys 613, girls 296) the prevalence of NAFLD, mea-
sured as surrogate of alanine aminotransferases (ALT),
was 33.4% in boys, and 19.6% in girls respectively.42
Race, ethnicity and degree of obesity significantly pre-
dicted the presence of fatty liver, with Hispanics having
the highest and African Americans the lowest figure.43
One study with 181 consecutive asymptomatic obese
children demonstrated that 8% had an elevated ALT sug-
gestive of NAFLD, but the prevalence decreased in black
As shown in table II, studies on prevalence of NAFLD
in overweigh/obese children report values ranging from
8% to 80% (USA), depending upon the methods used for
the diagnosis.45-50 Unfortunately, most studies have been
limited to the use of indirect measures such as elevated
serum (ALT) and ultrasound to predict histological out-
come,51 but up to a 20% of young patients have normal
values of liver enzyme at the time of biopsy, despite hav-
ing histological proven NASH and/or fibrosis.52 Data
Table II. Data of prevalence of NAFLD/NASH in obese children from
19.6%° and 33.4%^
§Number of overweight/obese children included in the study.
* Percentage of presumed NASH.
° Girls ^ Boys
Table I. Prevalence/incidence of type 2 diabetes mellitus in youth.
CountryStudy and population Prevalence/incidence%Ref.
N = 427 obese/overweight subjects, Age 10.7 ± 3.5
N = 214 obese and normal weight subjects, Age 8-10
N = 520 obese/overweight subjects, Age 8.9-20.4
N = 102 with Metabolic syndrome, Age 7-18
N = 721 school-leaving boys, mean age 15.5 ± 0.7
N = 250 obese/overweight subjects, Age not provided
N = 234 obese/overweight subjects, Age 5-22
N = 514 obese/overweight subjects, Age 13.6-14
N = 105 obese and normal weight subjects, Age 10-18
N = 196 obese subjects, Age 7-18
N = 169 obese subjects, Age 7-18
IGT: 7%, T2DM: 1.6%26
IGT : 6.5%, T2DM 0.5% 27
IGT: 5.2%, T2DM: 1.5%28
IGT: 36%, T2DM: 6%
IFG 0.41%, T2DM 0.83% (lean individuals)
‡IGT, T2DM 2.5% (obese/overweight)
‡IGT 13.6%, T2DM 1.2% 31
IGT, T2DM: 13.5%32
IGT 5.4%, T2DM 0.5%33
IGT 18%, T2DM 3%
Prepubertal IGT 19%, T2DM 2%
Pubertal IGT 27.5%, T2DM 4.3%
We included exclusively data from studies published in the list five years and using standard glucose tolerance test to assess impaired glucose tolerance (IGT) and type 2 diabetes
mellitus according to the ADA criteria. In few studies diagnosis was made according to the WHO criteria. (‡). Some articles were not accessible through the website, therefore the
abstract alone was available.
A Alisi et al. NAFLD and T2DM
from NHANES in 2450 adolescents found elevated ALT
in 6% of overweight and 10% of obese subjects.53 Simi-
larly, the 1998 Korean National Health and Nutrition Ex-
amination Survey found a prevalence of elevated ALT as
high as 3.2%.54 In a sample of Mexican obese/overweight
children from an elementary school, elevated ALT were
observed in 42% of subjects.55
Based on ultrasonography evidence of fatty liver,
NAFLD was diagnosed in 2.6% of Japanese children and
occurrence of disease correlated significantly with indices
of obesity such as the body mass index;56 42% of 375, and
44% of 268 morbidly obese Italian children had hepatic
steatosis;57,58 among 123 obese Chinese children, 99 sub-
jects showed abnormal hepatic sonograms and 54 were di-
agnosed as NASH.59 Some studies combine data from ul-
trasonography and elevated ALT; for instance a study
demonstrating that 52.4% of obese Turkish children had
fatty liver by ultrasonography and 13.8% had high ALT
levels.60 According to an Italian survey in 195 obese chil-
dren, 55% had liver steatosis by ultrasonography, 20%
had elevated ALT and AST levels, and 15% had both.61
Type 2 diabetes: pathogenetic mechanisms
T2DM is caused by a combination of increased insu-
lin resistance and decreased insulin secretion. Peripheral
insulin-resistance is tightly coupled with obesity in chil-
dren and seems to be the major driving force of deterio-
rating glucose metabolism, and is also associated with
lipid partitioning in specific compartments (i.e., viscera,
muscle and liver). On the other hand, the reduction of in-
sulin secretion is probably a secondary event evolving
Insulin resistance is an impairment of the physiologic
effects of insulin on glucose.63 Normal glycemic control
requires the pancreatic β-cell sensing of glucose concen-
tration, synthesis and release of insulin, binding of insu-
lin to receptors with a consequent activation of several
signaling proteins. The activation of multiple signaling
cascade causes increased glucose uptake by muscles, fat,
and liver and decreased glucose production by the liv-
er.64 These molecular mechanisms are all altered in
T2DM, causing insulin resistance in muscle tissue, de-
creased pancreatic insulin secretion, and increased hepat-
ic glucose output.65
In children and adolescents with T2DM, defects of
glucose metabolism are characterized by a decline in the
first phase sensitivity of the β-cell coupled with the de-
cline of both first and second phase sensitivity.66 The dy-
namics of the impaired glucose metabolism in childhood
seem to be faster than in adults, representing a limited
window of opportunity for successful preventive inter-
vention. Early identification of children with altered glu-
cose metabolism is important in order to quantify public
health needs and to allocate resources for appropriate
The risk factors for developing type 2 diabetes in
youth include a genetic predisposition and certain envi-
ronmental characteristics.67 The majority of diabetes in
both adults and children is polygenic.68 Thus, the family
history of diabetes represents the most important risk fac-
tor of developing T2DM with respect to the general pop-
Ethnicity is another important factor predisposing to
T2DM development. The increased incidence of T2DM
in youth of color was identified first in the Pima Indians
of the southwest. Children of Pima Indian were found to
have high rates of morbid obesity and from 1980 the re-
search has focused on this group as well as other ethnic
and racial groups with high rates of diabetes.70 Low birth-
weight, maternal diabetes and the intrauterine environ-
ment also are important areas to consider in risk for the
development of T2DM in youth.71 Puberty coupled with
insulin resistance provides a strong basis for the develop-
ment of pre-diabetes and T2DM in youth with over-
weight or frank obesity.72
The changing environment during the past several de-
cades provided a further contribution of the dramatic in-
crease in T2DM in youth. There has been a movement to-
ward a positive energy balance due to diet intake, de-
creased physical activity and increased sedentary activity.
Fast food consumption and portion sizes have increased
from 30 years ago, leading to caloric intake in excess of
metabolic need, and youth are the major consumers of fast
food meals. Moreover, youth are increasingly inactive, re-
ducing their physical activity and using sedentary screen
activities, such as television viewing and playing video
games, for an average of 5.5 hours daily.67
All these evidence demonstrate that development of
T2DM in youth is complex and requires astute health
care providers who understand the pathophysiology, pa-
tient history, family history, and genetic predisposition,
coupled with environmental factors, to manage each
youth at the appropriate intervention level.
NAFLD: pathogenetic mechanisms
The pathogenesis of NAFLD is not yet completely un-
derstood, however a currently favored hypothesis is that
«two hits» are required for a subject to develop the dis-
ease.73 A first hit that provokes steatosis (i.e. fat accumu-
lation in liver and/or insulin resistance) and predisposes
the liver to a second hit which leads to necro-inflamma-
tion and fibrosis. This second hit includes the alteration
of several signaling pathways regulating oxidative stress,
mitochondrial dysfunctions and production of pro-in-
flammatory and pro-fibrotic cytokines and their signal-
ing. Recent advances demonstrate that fatty liver and its
progressive development in NASH is a more complex
phenomenon which originates by multiple hits.74,75 In
fact, the subsequent development of fibrosis requires
probably the coexistence of multiple factors, including
Annals of Hepatology 8(1) 2009: S44-S50
ESTE DOCUMENTO ES ELABORADO POR MEDI-
served a prevalence of IGT as high as 9% and T2DM of
2%. The degree of insulin resistance was not correlated
with liver histology in terms of grade of steatosis, inflam-
mation or fibrosis. Subjects with IGT/T2DM did differ
from normo-tolerant individuals neither in anthropomet-
rics or liver histology. Conversely the prevalence of
overt MetS was higher in subjects presenting with fibro-
sis and/or NASH.14 The limited number of subjects with
impaired carbohydrate metabolism did not allow exclud-
ing that visceral adiposity (i.e. through reduced levels of
adiponectin or increased pro-inflammatory adipocytok-
ines) mediates both derangements in liver histology and
host (genes) and environmental factors as well as those
related to lifestyles and behaviors.76,77
All today theories consider insulin resistance as an
important driving force, which promotes lipolysis of pe-
ripheral adipose tissue which, in turn, increases free fatty
acid (FFA) influx into the liver.78 Hyperinsulinemia and
hyperglycemia promote de novo lipogenesis and inhibit
simultaneously FFA oxidation.79 Fatty deposition at the
liver side is also favored by defective incorporation of
triglyceride into apolipoprotein carrier proteins and lipid
Fatty loaded hepatocytes are susceptible of additional
insults, which may lead to hepatocyte injury, inflamma-
tion, and fibrosis. Also the role of oxidative stress is well
documented in NASH., There is accumulating evidence
that oxidative stress and mitochondrial dysfunction play
a key role in the physiopathology of NAFLD/NASH
whatever its initial cause.81 Moreover, there is a close in-
teraction between development of mitochondrial dys-
function, insulin resistance and cytokines in many liver
diseases.82 Conversely, many forms of oxidative stress
lead to antioxidant depletion, which then further en-
hances oxidative stress and cytokine-mediated hepatox-
icity.83 In addition, although the exact mechanisms pro-
moting progressive liver injury are not well defined, also
substrates derived from adipose tissue such as FFA, tumor
necrosis factor alpha, leptin, and adiponectin have been
Taken together, all discussed evidences highlight the
complicated network of interactions existing among the
several molecules and signaling pathways which contrib-
ute do development of NAFLD/NASH. Thus, today it is
impossible to distinguish between causes or effects dur-
ing NAFLD/NASH development and progression.
More than a clinical association
The NHANES found NAFLD to be more prevalent in
obese race minorities, with T2DM, hypertension and hy-
perlipidemia.86 These associations have led to the hy-
pothesis that NAFLD may precede the onset of type 2 di-
abetes in some individuals. But, why should NAFLD as-
sociate with diabetes? The links between the two
diseases reflect processes related to insulin action or re-
sistance which may be mediated through the location
and function of fat, excess total body fatness or hepatic
fat. Otherwise, the risk for new onset diabetes may be me-
diated by components of the MetS which occur very fre-
quently in NAFLD.
NAFLD, as estimated by elevated ALT levels, and pre-
diabetes or T2DM were found to be associated indepen-
dently of confounders, including obesity in adults.87 The
West of Scotland Coronary Prevention Study, consistent-
ly with a number of other studies, found that compared
with men with values for baseline ALT in the bottom
quartile (< 17 U/L), those with levels in the top quartile
(> 29 U/L) had an adjusted odds ratio of 2.04 (95% CI
1.16–3.58) for incident diabetes.88 In the British Hearth
Regional Study, the risk of type 2 diabetes increased sig-
nificantly with increasing levels of ALT and gamma-
glutamil-transpeptidase (GGT), even after adjustment for
a range of confounders, again including BMI (top vs bot-
tom quartile, ALT: RR 2.72, 95% CI 1.47–5.02; GGT:
RR 3.68, 95% CI 1.68–8.04) or with further additional
adjustment for insulin resistance.89
Data on the association between T2DM and NAFLD
in paediatric settings are poor, but nevertheless very
strong. In the San Diego series of biopsy proven NAFLD,
6 out of 43 children had type 2 diabetes mellitus
(14%).49,90 In our series of 120 babies,14 all subjects un-
derwent oral glucose tolerance test and diagnosis of im-
paired glucose tolerance or T2DM was done according to
the criteria of the American diabetes Association. We ob-
Also in youth, T2DM and NAFLD seem to be signifi-
cantly associated. The meaning and the causative rela-
tion of this finding is still unclear. It is likely that the in-
sulin resistant phenotype, charactering non alcoholic fat-
ty liver disease, contributes to anticipate significantly
the onset of type 2 diabetes from mature adulthood to
youth. This observation may translate into the worrisome
anticipation of all cardiovascular abnormalities linked to
T2DM. In addiction, NAFLD may represent an indepen-
dent risk factor which augments further the total cardio-
vascular risk. Therefore, both NAFLD and T2DM em-
body a growing healthcare burden which will boost
health related costs in the next future.
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