Influence of dietary intake and physical activity on annual rhythm of human blood cholesterol concentrations

Seasonal variation in the plasma total cholesterol (TC) and high-density li poprotein cholesterol (HDL-C) have been repeatedly reported, with contradic tory results regarding the pattern of seasonal variation of these parameter s. Furthermore, it is still not well established whether the variation is d ue to changes in the nutrition or changes in physical activity depending on the season. The aim of this study was therefore to determine plasma TC and HDL-C in different groups of healthy participants: 19 vegetarians with a c onstant diet independent of the season, 14 athletes with almost constant ph ysical activity over the year, and 114 controls in the age groups 20-26 yea rs (mean age 24 + 1.5 years) and 40-48 years (mean age 44.3 + 2.1 years). O ver 2 years, blood samples were collected every 2-3 months and were analyze d for plasma TC and HDL-C. At all visits, body mass index (BMI) and waist-t o-hip ratio (WHR) were calculated, and nutrition and physical activity prof iles were obtained. The seasonal model was calculated using object-oriented software for the analysis of longitudinal data in S (OS-WALD); multiple re gression analysis was used to determine the influence of age, gender, diet, and physical activity on seasonal changes of thr lipid parameters. In all groups, we found an annual rhythm of the plasma TC and HDL-C concentrations , which can be mathematically described by a sine curve with a maximum in w inter and a minimum in summer. This rhythm was independent of the age, gend er, BMI, diet, or physical activity. The observed seasonal differences betw een the maximum and the minimum were about 5%-10% for TC and about 5%-8% fo r HDL-C concentration. These differences were greater than the determined c ircadian (TC 3.5%, HDL-C 4%) and day-to-day changes for TC and HDL-C (coeff icient of variation <5% for both). In conclusion, annual rhythm of TC and H DL-C is not primarily induced by seasonal differences in dietary intake or physical activity. Therefore, the annual rhythm in cholesterol levels is mo st likely determined by endogenous factors or factors directly related to s easonal changes in the environment.