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Cholesterol levels rise in the winter, according to research presented during the American College of Cardiology's annual meeting. Previous studies showed that heart attacks and cardiac mortality peak during the winter, so researchers at Johns Hopkins University, Baltimore, looked at changes in seasonable lipids in 2.8m adults.

LDL and non-HDL cholesterol levels were 3.5 and 1.7 per cent higher in men and women respectively during the colder compared to warmer months. Triglycerides were 2.5 per cent higher in men during the winter. HDL did not vary much between seasons.

€In this very large sample, we found that people tend to have worse cholesterol numbers on average during the colder months than in the warmer months €“ not by a very large amount, but the variation is significant,€ said lead investigator Parag Joshi, cardiology fellow, Johns Hopkins Hospital. €It confirms findings from smaller studies and raises a lot of interesting questions€ €“ not least the cause of the fluctuations.

Behavioural changes seem to be partly responsible. €In the summer, we tend to get outside, we are more active and have healthier behaviours overall,€ Dr Joshi said. €In the colder months, we tend to crawl into our caves, eat comfort foods and get less exercise, so what we see is that LDL and non-HDL are slightly worse.€

In addition, the limited time spent outside means less sun exposure. The resulting lower concentration of vitamin D worsens lipid profiles. However, researchers still need to identify the causes of these seasonal variations.