A longitudinal study of the biological variability of plasma lipoproteins in healthy young adults.

The fasting serum concentrations of total cholesterol, low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), total triglyceride and apoprotein A1 were measured at intervals of 12-18 weeks for 60 weeks in 17 male and 11 female healthy young adults in order to assess the variability of these risk factors for coronary disease. No statistically significant seasonal changes were detected in any variable in either sex, although a progressive rise in apoprotein A1 concentration was observed. The coefficients of variation for random fluctuations with time were in the rank order: total cholesterol less than HDL-C less than apoprotein A1 less than LDL-C less than triglyceride. These differences were attributable to biological, rather than to methodological, factors. Within subjects, HDL cholesterol concentration varied inversely with triglyceride concentration and directly with apoprotein A1 concentration. The marked differences which exist in the biological variability of lipid risk factors for atherosclerosis need to be taken into account when making comparisons in epidemiological studies of the predictive powers of single on-entry measurements for future disease. Fluctuations of HDL-C with time appear to be related in part to variations in triglyceride-rich lipoprotein metabolism.