The conjoint trait of low high-density lipoprotein cholesterol and high triglycerides in adolescent black and white males

Abstract

To evaluate the interrelationships among body composition, blood pressure, and lipid phenotypes in adolescent black and white boys, we assessed racial distributions of lipids, blood pressure, and obesity and their joint occurrence in black and white boys aged 10 to 15 years. Subjects were recruited from Cincinnati (OH) schools. Because the differences in high-density lipoprotein cholesterol (HDL-C) and triglycerides (TGs) are the most profound coronary heart disease (CHD) risk factor differences between black and white males, we assigned subjects to one of four low-HDL-C and high-TG categories (normal and increased risk) using the age/race-specific 25th (HDL-C) and 75th (TG) percentiles. We then assessed racial distributions of lipids, blood pressure, and obesity by these phenotypes. Age differences between the black and white participants were significant, with the former about 3 months younger ( P = .03), but black boys were more mature and were significantly taller and heavier and had a greater body mass index ([BMI] weight in kilograms divided by height in centimeters squared). Differences in the sum of the triceps, subscapular, and suprailiac skinfolds were not significant. Blacks had significantly higher HDL-C, lower TG, and higher diastolic blood pressure (DBP), but differences in systolic blood pressure (SBP) were not significant. In both racial groups, the body composition measures were significantly correlated with HDL-C, TG, and blood pressure levels; the correlations between HDL-C and both weight and BMI were significantly stronger in white boys. The proportion of boys of each race with low HDL-C and high TG was similar by design. In both racial groups, subjects with the conjoint trait had a significantly greater BMI, triceps skinfold, and sum of skinfolds than subjects in the other phenotypic groups. For white boys, participants with the conjoint trait had the highest SBP and DBP; differences in SBP were significant for comparisons to the normal- and high-TG group alone, and differences in DBP were significant for the comparison between normal and low HDL-C alone. For black boys, subjects with both normal HDL-C and TG had significantly lower SBP than boys with either the conjoint trait or high TG alone; none of the group differences in DBP were significant. Black had significantly less dense LDL (more LDL-C per apolipoprotein [apo] B). In each racial group, boys with the conjoint trait had the most dense LDL, significantly more dense than in any of the other phenotypes in black boys and significantly more dense than in boys with low HDL-C alone and normal boys in the white group. In both racial groups, the occurrence of no risk factors (>75th percentile TG, BMI, SBP, and DBP or <25th percentile HDL-C) and three or more risk factors was greater than expected by chance alone, and the occurrence of exactly one risk factor and two factors was less. When examined by phenotypic groups within race, boys in each racial group with the normal phenotype had a greater than expected percentage with no risk factors, and white boys with the conjoint trait were more likely to have a marked increase in multiple risk factors. Possible mechanisms for this clustering of risk factors and for the racial differences in the patterns are discussed.