|The metabolic syndrome is a cluster of multiple risk factors
for cardiovascular disease and diabetes that are deserving of more
clinical attention. In 1988, Reaven reported that several risk factors
like hypertension, dyslipidemia, and hyperglycemia commonly
cluster together . In 1998, World Health Organization proposed
the first formalized definition using the term metabolic syndrome
. Then, various diagnostic criteria have been proposed by different
organizations over the past decade [2-15]. In Japan, a consultation group
on the definition of metabolic syndrome identified abdominal obesity
as the major underlying risk factor and a prerequisite component for
diagnosis of metabolic syndrome . However, there has been a debate
as to whether this feature should be a mandatory clinical criterion and
additional inspection has been necessary.
|The MEtabolic syndRome and abdominaL ObesiTy (MERLOT)
study  is a single-center, hospital-based non-concurrent prospective
cohort study designed to investigate the significance of abdominal
obesity on components of the metabolic syndrome including high blood
pressure, dyslipidemia, and hyperglycemia. The study included 25,255
subjects, aged 21 and 70 years old, underwent a corporate subsidized
general health check program annually from 1994 to 2010. Using
this cohort, we investigated whether intra-abdominal fat area (IAFA)
measured by computed tomography is an independent predictor for
the new onset of individual components of the metabolic syndrome in
healthy Japanese. During 3.6 years of the mean follow-up period, one of
metabolic syndrome components occurred in 54% of healthy subjects.
The multiple Cox regression analysis disclosed that IAFA is significantly
associated with onset of metabolic syndrome components (hazard
ratio: 1.37 per 1SD, 95%CI: 1.28-1.46). This finding was independent of
body mass index (BMI), and significant even in non-obese individuals
with BMI <25 kg/m2. There was no significant difference in test for
interaction between obese (BMI ≥ 25 kg/m2) or non-obese (BMI <25
kg/m2) and IAFA in predicting metabolic syndrome components
(p=0.278). Thus, IAFA can be a better predictor for the new onset
of cardiometabolic risk factors and play an important role among
parameters in rational cardiometabolic risk stratification of health
people, especially in normal BMI.
|While IAFA may be a uniquely important pathophysiological fat
depot in cardiometabolic risk [18,19], there has been much debate
regarding the role of abdominal subcutaneous fat area (aSFA). Some
studies have suggested a beneficial role of abdominal subcutaneous fat
adiposity . Other studies found that aSFA was inversely correlated
with subclinical atherosclerosis and the occurrence of metabolic
syndrome . Furthermore, some studies assessed which is more
strongly associated with cardiometabolic risk, IAFA or aSFA [19,22].
The previous cross-sectional study revealed that both IAFA and aSFA
are associated with cardiometabolic risk profile but IAFA is more
strongly associated with an adverse metabolic risk . We have
observed similar results in the longitudinal analysis from the MERLOT
study. However, it is difficult to separate the effects of IAFA from aSFA
because of the highly correlation between IAFA and aSFA and further
evaluation is needed.
|More recently, the Framingham Heart Study reported fat quality
of intra-abdominal adipose tissue and subcutaneous adipose tissue
evaluated by lower computed tomography attenuation as measured in Hounsfield units was associated with adverse cardiometabolic risk .
This was independent of IAFA and aSFA, suggesting the fat quality is
associated with cardiometabolic risk factors above and beyond absolute
levels of fat volumes. Future research on this topic may help to determine
the underlying pathophysiology of obesity and cardiometabolic risk
|Now, Japan face growing challenged from super aging and
noncommunicable diseases. As the rising health care costs of the
government relating to noncommunicable diseases, the spotlight
is on the prevention and control of those diseases, as the means of
ensuring sustained health for the elderly. In 2008, Japan developed the
pioneering approach to quash national obesity (especially abdominal
obesity). Under the national law, companies and local governments
must evaluate abdominal obesity for citizens between the ages of 40 and
74 as part of their annual checkups. If these individuals exceed the limit,
they are considered at risk for obesity-related conditions like diabetes
and heart disease and are offered exercise and dieting guidance. If after
six months they still don’t meet the requirement, they are given further
re-education. We are working on the analysis of the “big data” and will
provide new insight regarding abdominal obesity.
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