When the seasons change, your immune system response may also change, British researchers report.
Some conditions worse in winter
These findings might explain why conditions such as rheumatoid arthritis and heart disease are worse in the winter than in the summer, the new study finds.
The researchers from the University of Cambridge analysed genes from more than 16,000 people worldwide, including those from both the Northern and Southern hemispheres. They found that the activity of nearly one-quarter of the genes differed according to the time of the year. Some are more active in winter and some are more active in summer, the research revealed.
Seasons also affect our immune cells, and the composition of our blood and fat, according to the study.
Read: Genetics: the basics
Findings were published in the journal Nature Communications.
It's been known that there are seasonal variations in a number of conditions, including heart disease, autoimmune disorders such as type 1 diabetes, multiple sclerosis and mental illness, as well as in vitamin D metabolism. However, the researchers said this is the first study to show that seasonal changes may affect immune system function.
"In some ways, it's obvious – it helps explain why so many diseases, from heart disease to mental illness, are much worse in the winter months – but no one had appreciated the extent to which this actually occurred," said John Todd, professor and director of the JDRF/Wellcome Trust Diabetes and Inflammation Laboratory at the University of Cambridge.
"The implications for how we treat disease like type 1 diabetes, and even how we plan our research studies, could be profound," he said in a university news release.
One gene that was more active in the summer and less active in the winter has been shown to suppress inflammation in mice. If the same is true in people, those in the Northern Hemisphere would have higher levels of inflammation in the winter.
Inflammation is a risk factor for a number of diseases, which means that those at high risk might be more likely to have more health problems during the winter. Drugs that target inflammation may offer a way of treating these diseases more effectively in the colder months, the researchers suggested.
They also found that certain genes associated with people's responses to vaccines were more active in winter. This means that some vaccination programmes might be more effective during that season.
"Given that our immune systems appear to put us at greater risk of disease related to excessive inflammation in colder, darker months, and given the benefits we already understand from vitamin D, it is perhaps understandable that people want to head off for some 'winter sun' to improve their health and well-being," Todd said.
Exposure to the sun triggers vitamin D production in the body.
Image: Happy woman in winter from Shutterstock