Cyclic seasonal variation in plasma lipid and lipoprotein levels: the Lipid Research Clinics Coronary Primary Prevention Trial Placebo Group.

Seasonal plasma lipid and lipoprotein cycles were studied in 1446 hypercholesterolemic 35-59 year-old men followed for 7 years as the placebo group of the Lipid Research Clinics (LRC) Coronary Primary Prevention Trial (CPPT). Separate periodic time series were calculated for each study participant; mean parameter estimates were obtained by vector algebra. Highly significant (p less than 0.001) synchronous sinusoidal seasonal cycles, peaking in the first month of winter, were demonstrated for plasma levels of total (TOT-C), low-density lipoprotein (LDL-C), and high-density lipoprotein (HDL-C) cholesterol. Their mean seasonal changes (nadir to zenith) were 7.4, 6.4, and 0.8 mg/dl, respectively. An irregular but statistically significant seasonal pattern was also observed for plasma triglyceride (TG) levels, with peak levels in the autumn. The variation of these seasonal effects among subgroups and geographic locales and their correlation with seasonal weight and dietary patterns yielded few clues as to their underlying etiologic mechanisms.