The triglyceride paradox in people of African descent

Abstract

Even though insulin resistance, cardiovascular disease (CVD), and type 2 diabetes (T2D) are associated with hypertriglyceridemia, blacks with these conditions usually have normal triglyceride (TG) levels. This is often called a lipid paradox. More precisely, it is a "TG paradox." The pathways that lead to hypertriglyceridemia have been intensively explored. Yet, the pathways that allow TG levels to be normal in the presence of insulin resistance have received little attention and this is problematic. Tests designed for the early detection of insulin-resistant conditions often use elevated TG levels as a diagnostic criterion. However, insulin resistance, CVD, and T2D are not usually associated with hypertriglyceridemia in people of African descent; therefore, the widespread use of TG levels to predict these conditions needs re-evaluation. This review focuses on black-white differences in: (1) the lipid profile across North America, Europe, and Africa; (2) the efficacy of TG-based screening tests, specifically the metabolic syndrome and its two abbreviated versions, the hypertriglycerdemic waist and TG/high-density lipoprotein cholesterol (HDL-C) ratio; and (3) the mechanisms that allow TG to be normal even in the presence of insulin resistance. Overall, a broader understanding of how TG physiology varies by race could lead to better diagnostic tests and improved health outcomes.

FIG. 1.

Comparison of metabolic variables in African men living in the United States and African-American men. (Black) Africans living in the United States; (gray) African Americans. (A) Systolic blood pressure (SBP); (B) diastolic blood pressure (DBP); (C) fasting glucose; (D) 2-h glucose after an oral glucose tolerance test (OGTT); (E) visceral adipose tissue (VAT) area; (F_ metabolic syndrome prevalence. For parts A–E, data are presented as mean±standard error (SE) with comparison by the Student's t-test. For panel F, data are presented as percent with comparison by chi-squared. (*) P<0.05; (**) P<0.01. Data were adapted from Ukegbu et al.

FIG. 2.

Prevalence of diagnostic variables in West Africans and African Americans with metabolic syndrome. HDL-C, high-density lipoprotein cholesterol; BP, blood pressure; WC, waist circumference; TG, triglycerides. (Reproduced with permission from SumnerAE et al., CVD Prevention 2010;5:75–80.

FIG. 3.

Frequency distribution of triglyceride (TG) levels in men with the metabolic triad. (Top) Africans living in the United States; (bottom) African-American men. The dotted line represents the TG threshold for hypertriglyceridemic waist. Only 2 African men (top) and 2 African-American men (bottom) have both metabolic triad and hypertriglyceridemic waist (unpublished data).