Metabolic Syndrome in American Indians

The National Cholesterol Education Program Expert Panel on Detection, Evaluation and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III [ATP III]) recently proposed a formal definition of the metabolic (insulin resistance) syndrome (1). For the purposes of ATP III, metabolic syndrome is present when ≥3 of the following determinations are present: waist circumference >102 or >88 cm in men and women, respectively; triglycerides ≥150 mg/dl; HDL cholesterol <40 or <50 mg/dl in men and women, respectively; blood pressure ≥130/≥85 mmHg; and fasting glucose ≥110 mg/dl.

Data from the Third National Health and Nutrition Examination Survey (NHANES III) show that among U.S. adults ≥20 years of age, metabolic syndrome is present in 23.8, 21.6, and 31.9% of whites, blacks, and Hispanics, respectively (2). NHANES III does not include data for American Indians. The baseline examination of the Strong Heart Study (SHS), a longitudinal, population-based study of cardiovascular disease (CVD) and CVD risk factors in 4,549 American Indians, was concurrent with NHANES III . Therefore, SHS data provide a unique opportunity to contrast the dramatic ethnic differences in prevalence of metabolic syndrome between American Indians and other ethnic groups in the U.S. The prevalence of metabolic syndrome in SHS men aged 45–49 years was 43.6% compared with 20.0% among all men in NHANES III, a prevalence ratio of 2.18. The prevalence of metabolic syndrome in SHS women in the same age group was 56.7% compared with 23.1% among NHANES III women, a ratio of 2.45.

Ethnic differences in prevalence of metabolic syndrome between SHS men and NHANES III men diminished with age, resulting in similar prevalence rates in the 60–69 and 70–74 age groups (∼43% for both SHS and men in both age groups). In contrast, the prevalence of metabolic syndrome in SHS women was considerably higher than that in NHANES III women, even in the older-aged participants. In the 60–69 and 70–74 age groups, the prevalence ratio contrasting SHS women to NHANES III women was 1.56. The overall prevalence of metabolic syndrome was 55.2% in SHS participants aged 45–74 years.

The lack of increase in metabolic syndrome with age in SHS men may reflect maintenance of a traditional lifestyle among men of older generations and/or selective mortality among less healthy older men. The high prevalence of metabolic syndrome among older SHS women may reflect relatively better survival with CVD risk factors and/or earlier adoption of a sedentary lifestyle. Metabolic syndrome among American Indians is likely a combination of genetics (3) and environmental factors, such as low physical activity and obesity. The high prevalence of metabolic syndrome in American Indians may, in part, explain the rapidly increasing rates of CVD in this population (4). Additional efforts are needed to achieve desirable practice patterns that are sufficient to meet the needs of people with metabolic syndrome. This is especially pressing for American Indians, in whom the high prevalence of metabolic syndrome and increasing CVD rates underscore the need for effective treatment of risk factors.