Prospective 10-year evaluation of hypobetalipoproteinemia in a cohort of 772 firefighters and cross-sectional evaluation of hypocholesterolemia in 1,479 men in the National Health and Nutrition Examination Survey I

Abstract

Our specific aim in a 10-year prospective study of 772 Cincinnati firemen (predominantly aged 26 to 46 years) was to determine the prevalence, attributes, and etiology of persistent hypobetalipoproteinemia, defined by entry low-density lipoprotein cholesterol (LDLC) less than 75 mg/dL. A second specific aim was to cross-sectionally assess hypocholesterolemia (defined by total serum cholesterol [TC] < 130 mg/dL) in 1,314 white and 165 black men aged 26 to 46 years in the National Health and Nutrition Examination Survey (NHANES I). The 141 black and 631 white firemen had 4,973 person-years of follow-up time (median, 7.1 yr/man). Of 772 men, 44 (5.7%) had entry LDL levels less than 75 mg/dL; they had a mean follow-up time of 7.3 yr/man. Of these 44 men, there were 12 (1.6% of the cohort) with entry LDLC less than 75 mg/dL, and at least 67% of their follow-up LDLC levels were less than 75. Their mean entry TC and LDLC levels were low (130 and 58 mg/dL), mean triglyceride (TG) was low (63 mg/dL), and mean high-density lipoprotein cholesterol (HDLC) was high (60 mg/dL). LDLC remained at less than 75 mg/dL in 81% of their follow-up samples. Their mean entry and follow-up cholesterol and LDLC did not differ ( P > .1, 130 v 133 mg/dL and 58 v 63 mg/dL). Compared with 32 men with entry LDLC less than 75 mg/dL but with less than 67% of follow-up LDLC less than 75 mg/dL, the 12 men with persistently low LDLC had lower mean Quetelet indices and diastolic blood pressure at entry (2.36 v 2.58, P = .056; 73 v 80 mm Hg, P = .03) and on follow-up study (2.45 v 2.69, P = .04; 72 v 79 mm Hg, P = .05). Of 12 men with persistently low LDLC; two had truncated apolipoprotein (apo) B (familial hypobetalipoproteinemia), two had the apo E genotype 2 3 , and two had acquired hypobetalipoproteinemia that antedated mortality from melanoma by 9 years and from alcoholism by 2 years. Comparable to white and black firemen aged 26 to 46 years, 2.9% and 3.6% of whom had entry serum TC less than 130 mg/dL, of 1,314 white and 165 black men in the NHANES I study (aged 26 to 46), 1.8% and 3.6% had hypocholesterolemia (entry TC < 130 mg/dL). Daily mean calorie, fat, and protein intake (grams per day) did not differ ( P > .05) in men with entry TC less than 130 mg/dL compared with those with TC 130 to 230 or greater than 230 mg/dL. Hypocholesterolemia in white and black men in NHANES I could not be attributed to hypocaloric intake or to protein, fat, or carbohydrate undernutrition. There appear to be racial differences in the prevalence of hypocholesterolemia. Blacks comprised 18% of the firemen's cohort but 42% of those with persistent hypobetalipoproteinemia; among NHANES I subjects, 3.6% of blacks were hypocholesterolemic versus 1.8% of whites. Unless persistent hypobetalipoproteinemia reflects an underlying disease, alcoholism, etc., it is often heritable, and may be associated with a reduced likelihood of coronary heart disease (CHD) and with increased longevity.