Seasonal variation in serum cholesterol levels in health screening populations from the U.K. and Japan.

We have performed time series analyses on data from 140,000 men and 32,000 women in the U.K. and 30,000 men and 12,000 women in Japan, seen over periods ranging from 4 to 6 1/2 years, in order to test for seasonal variation in serum cholesterol levels. In both countries and both sexes we found a strong seasonal effect, with mean cholesterol levels being some three to five percent higher in winter than in summer. Mean monthly cholesterol levels were negatively correlated with mean monthly air temperatures (r = -0.60 to -0.71). The seasonal differences observed were independent of changes in body weight, and have important implications both for long-term epidemiological or follow-up studies, and for the interpretation of patient data.