In a new study, researchers have found that the seasons appear to influence when certain genes are active in your body, with those that cause inflammation being more active in winter.
For the new study, researchers looked at the genes of 16,000 people and found that the activity of about 4,000 of those genes that appear to be affected by the season. The findings were reported in the journal Nature Communications. The findings could help explain why certain diseases are more likely to strike for the first time during certain seasons.
"Certain chronic diseases are very seasonal - like seasonal affective disorder or cardiovascular disease or Type 1 diabetes or multiple sclerosis or rheumatoid arthritis," says John Todd, a geneticist at the University of Cambridge who led the research. "But people have been wondering for decades what the explanation for that is."
When researchers began to look at exactly what genes were more or less active during some seasons, one thing jumped out.
"One of the standout results was that genes promoting inflammation were increased in winter, whereas genes suppressing inflammation were decreased in the winter. So overall it looked as if this gene activity pattern really goes with increased inflammation in the winter," he says.
Inflammation, which is caused by the immune system becoming overactive, Todd says, has long been associated with a lot of the health problems that spike in the winter. No one knows how the seasons affect our genes. But there are some obvious possibilities, Todd thinks.
"As the seasons come on it gets colder, the days get shorter," he says. "So daylight and temperature could be factors."
Some researchers believe these findings could have far reaching implications.
"The fact that they find so many genes that go up and down over the seasons is very interesting because we just didn't know that our bodies go through this type of seasonal change before," says Akhilesh Reddy, who studies circadian rhythms at the University of Cambridge but was not involved in the new research. "And if you look at the actual genetic evidence for the first time, it's pretty profound really."
Reddy believes that the findings will prompt other scientists to look at how the seasons may have power over our genes.
"People might have a variation in their responses to all sorts of things that we haven't really thought about yet," Reddy says.
"Even your cognitive performance ... might be influenced subtly by the time of year at which you're assessed," he says. "There's never been a marker before that you can look at in the blood, or whatever, to say, 'You're looking like you're a winter person now versus a summer person.' "
