Cholesterol levels fluctuate based on the time of year with more unfavourable lipid profiles seen in the colder months, an Indian-origin scientist has found.
The trend may be driven by behavioural changes that occur with the changing seasons, researchers said.
While previous studies have shown that heart attacks and heart-related deaths increase during the winter months, researchers at Johns Hopkins Ciccarone Center for the Prevention of Heart Disease were interested in finding out whether cholesterol parameters might follow a similar pattern.
They studied a sample of 2.8 million adults - the largest study to look at seasonal lipid trends in US adults to date. "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 Parag Joshi, cardiology fellow, Johns Hopkins Hospital, and lead investigator of the study.
"It confirms findings from smaller studies and raises a lot of interesting questions, including what might be driving these [fluctuations]," Joshi said.
"In the summer, we tend to get outside, we are more active and have healthier behaviours overall," Joshi said.
"In the colder months, we tend to crawl into our caves, eat [fat-laden] comfort foods and get less exercise, so what we see is that LDL and non-HDL [bad cholesterol markers are slightly worse.
"So you have a lipid signature of higher risk, but it's probably driven by a lot of behaviours that occur with the changing seasons," Joshi added.
Researchers speculate the shorter days of winter – and limited time spent outside - also mean less sun exposure and, subsequently, lower concentrations of vitamin D, which has also been associated with the ratio of bad to good cholesterol.
In the study, researchers analysed lipid profiles in US adults who were referred for testing by their doctors from 2006 to 2013.
Samples were categorised by the time of year when cholesterol was measured and comparisons were made across the seasons.
Total cholesterol, low density lipoprotein (LDL) and non-high density lipoprotein (non-HDL) cholesterol levels were all higher in the winter than in the summer.
LDL and non-HDL cholesterol were 4 mg/dL higher in men and 2 mg/dL higher in women during the colder vs warmer months - a 3.5 per cent and 1.7 per cent increase, respectively.
Triglycerides were 2.5 per cent higher in men during the winter compared with the