Seasonal variation in lipoprotein lipase and plasma lipids in physically active, normal weight humans.

Adipose tissue lipoprotein lipase (ATLPL) provides free fatty acids (FFA) for storage in adipocytes, whereas in skeletal muscle LPL (SMLPL) provides FFA for oxidation. In hibernating animals, the level of SMLPL is relatively higher in summer than winter (promoting fat oxidation), whereas the opposite is seen with ATLPL. A patient- controlled study was designed to determine whether such seasonal variation occurs in normal weight humans. Eighteen subjects were studied in the summer and winter. After 2 days of a standardized diet, they underwent muscle and adipose biopsies for LPL activity, assessment of fitness by VO2 max, and determination of body composition by hydrostatic weighing. The per- centages of body fat, body mass index, VO2 max, insulin, glucose, FFA, glycerol, and leptin were not affected by the season. Total cholesterol was higher in the winter than in the summer (157 6 5.5 vs. 148 6 4.2 mg/dL respectively; P 5 0.03). The ATLPL activity was also higher in the winter than in the summer (4.4 6 0.8 vs. 2.3 6 0.6 nmol FFA/10 6 cellszmin; P 5 0.04). SMLPL activity trended to be higher in the winter than in the summer (1.9 6 0.5 vs. 1.0 6 0.1 nmol FFA/gzmin; P 5 0.06). In summary, ATLPL is seasonally regulated. It appears that SMLPL is similarly regulated by season. For physically active lean subjects, this increase in SMLPL may be a compensatory mechanism to help protect from seasonal weight gain. (J Clin Endocrinol Metab 85: 3065-3068, 2000) H IBERNATING mammals are able to store large amounts of energy-rich lipids before hibernation, and part of the mechanism by which this is accomplished is through an increase in adipose tissue lipoprotein lipase (ATLPL) (1). Some studies have shown humans to also have a seasonal fluctuation in weight, with winter body mass index being almost 0.5 kg/m 2 greater than that in summer (2). In an uncontrolled retrospective analysis of ATLPL ac- tivity, Persson (3) found a seasonal variation, with activity being the highest in the winter and the lowest in the summer. However, this analysis did not control for patient differences or for seasonal changes in diet or activity levels. In addition to seasonal differences in weight and potential differences in lipoprotein lipase (LPL) activity, plasma lipids are known to vary seasonally. Numerous studies have dem- onstrated total cholesterol to be higher in the winter than the summer by an average of about 4% (4 -7). Additionally, low density lipoprotein (LDL) cholesterol (or apolipoprotein B) appears to increase in the winter (5, 8, 9), as does high density lipoprotein (HDL) cholesterol (5, 8, 10). Although triglycer- ides may vary seasonally and may be less in the winter than the summer (8, 11, 12), the variation in triglycerides does not appear to be related to the variation in cholesterol (2). The mechanism for these lipid changes with season is unknown. It does not appear to be due to diet (2), although one study has been able to abolish the seasonal effect with high dose vitamin C (13). Additionally, the lipid changes do not appear to be due simply to changes in temperature (2). The changes described above in LPL activity may also play a role. This study was designed to evaluate these questions in a prospective, patient-controlled manner. Specifically, the hy- potheses tested were: ATLPL will be highest in the winter (promoting storage) and lowest in the summer (promoting mobilization); SMLPL will be seasonally reciprocal to adi- pose tissue LPL; the variation will be due to seasonal dif- ferences in activity and/or body composition; and the vari- ation in LPL will account (in part) for the seasonal variation in lipids.