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Ethnic considerations of metabolic syndrome and body composition
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The prevalence of metabolic syndrome varies among different ethnic and racial populations. Blacks in the African Diaspora continue to have increasing cardiovascular diseases, type 2 diabetes and associated complications when compared with their white counterparts. Similarly, Indian Asians and Filipinos have higher rates of diabetes and its associated CV complications compared with whites.
Although the exact reasons may be multifactorial (genetic vs. environmental), there are intriguing metabolic and anthropometric differences in ethnic minorities residing in diverse geographic locations when compared with whites. During the past three decades, researchers from several studies have reported metabolic differences in people of the African Diaspora. Current data have shown that in general, blacks without diabetes are more insulin resistant and hyperinsulinemic than their white counterparts. Further, blacks residing in the Western world are more obese than whites. Most importantly, however, for identical BMI, blacks have lower intra-abdominal visceral adiposity than their white counterparts. National Health and Nutrition Examination Survey III data revealed that the presence of metabolic syndrome was lower in blacks when compared with whites.
The major confounders that account for the ethnic differences in metabolic syndrome between blacks and whites can be partly attributed to the higher levels of HDL and corresponding lower serum triglyceride levels in blacks when compared with whites. This is paradoxical since a key pivotal lesion purported to underlie metabolic syndrome is insulin resistance.
There is increasing controversy regarding whether conventional CV risk factors are similar among different ethnic groups. Results of recent studies have demonstrated that the prevalence of metabolic syndrome is higher in immigrant Indian Asians than in whites and blacks residing in the United Kingdom. We should note that immigrant Indian Asians residing in the United Kingdom are, in general, leaner than their white and black counterparts. However, Indian Asians with similar BMIs have higher visceral adiposity, greater insulin resistance, severe hypertriglyceridemia and, consequently, higher prevalence rates of CV risk factors than their European and black counterparts. Furthermore, researchers have reported that for similar BMI, Filipino Americans have higher rates of metabolic syndrome, insulin resistance and greater intra-abdominal visceral adiposity than whites and blacks. The paradoxical findings of higher obesity rates (BMI >30), greater insulin resistance and less metabolic syndrome in blacks — in contrast with the higher prevalence of metabolic syndrome in leaner ethnic populations, eg, Indian Asians and Filipinos — with severe insulin resistance calls into question whether the components of metabolic syndrome uniformly predict future CV outcomes and type 2 diabetes in minority populations.
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These inconsistent reports suggest that race/ethnicity–specific cutoff points and criteria for metabolic syndrome may be necessary to affirm the predictive values of the metabolic syndrome on future CVD and type 2 diabetes in each ethnic and racial population. Furthermore, and most importantly, prospective studies on the predictive values of each of the components of the metabolic syndrome for CVD in various ethnic and racial groups are urgently warranted. The time has come.
Kwame Osei, MD, is Ralph W. Kurtz Professor of Medicine and Exercise Physiology and Director of the Division of Endocrinology, Diabetes and Metabolism at Ohio State University Medical Center.