Seasonal variation of serum lipids in an elderly population

We investigated seasonal variation in serum lipids in 96 volunteers aged 65-74 years who were studied at 2-monthly intervals for one year. Periodic regression analysis revealed highly significant seasonal variation in serum total cholesterol and high-density lipoprotein (HDL) cholesterol. Peak levels for both occurred in winter with corresponding summer troughs. The seasonal difference for total cholesterol was 0.32 mmol/l (95% CI 0.23-0.41, p < 0.0001) and that for HDL cholesterol 0.16 mmol/l (95% CI 0.12-0.19, p < 0.0001). Low-density lipoprotein (LDL) cholesterol was highest in winter in men only (seasonal difference 0.27 mmol/l, 95% CI 0.15-0.39, p < 0.0001), and triglycerides were significantly greater in late winter for women only (seasonal difference 0.22 mmol/l, 95% CI 0.09-0.35, p = 0.002). The timing of seasonal variation in total cholesterol and triglycerides would be consistent with a role in the seasonal variation in vascular deaths, but our finding of a relatively high HDL: total cholesterol ratio in winter makes this less likely.