Winter Sucks Because Our Genes Behave Differently With the Seasons

Winter is generally a shitty time to be a human. Aside from the snow and obligatory family visits, we get sicker: a whole range of conditions, from heart disease to mental illnesses, are worse and occur more frequently in winter months.

A new study unearths a potential cause for this seasonality: our gene activity changes with the seasons.

The study, published Tuesday in Nature Communications, found that over one in five genes tested showed different activity depending on the time of year, and that this affected the immune cells too.

"When we looked at the role those genes play in the body, we saw that the immune system was more active in winter, there was a pro-inflammatory environment in our bodies, and genes that had roles in metabolism were more active," explained Chris Wallace, a researcher at the University of Cambridge's Department of Medical Genetics and an author on the paper.

This makes a lot of sense: We know that, historically, infectious diseases caused a lot of deaths in the winter. "In winter, when the infectious diseases were peaking, it was advantageous to have an immune system that was highly active and able to respond to those diseases quickly and help you not die," Wallace said in a phone call.

So we could have developed the seasonal change as an evolutionary advantage (temperature and sunlight are also hypothesised to play a role in the mechanism). But this gene activity might now be more of a burden than a help, because we're better at dealing with infectious diseases thanks to sanitation and medicine. But having increased inflammation and immune system activity in the winter as a side effect of this changing gene activity can exacerbate all kinds of other conditions.

In autoimmune diseases, the immune system effectively attacks itself, so having it be more active isn't advantageous. In cardiovascular disease, inflammation can constrict the blood vessels and therefore exacerbate the chance of a heart attack.

It's not the genes themselves that change—you're stuck with them—but the way they behave in your cells. The researchers started by looking at gene activity in European winters, but what's incredible is that they saw the same kind of activity in Australian winters—even though the seasons are six months apart.

They even included a population from the Gambia in Africa, where they found that there were more inflammatory cells in the rainy season. That's not winter or summer, but is the time malaria hits. "Again, that makes sense in relation to infectious diseases: You would want an inflammatory environment to help you counter a malaria attack," said Wallace.

Altogether, the researchers examined samples from 16,000 people altogether; the work was funded by the Wellcome Trust and diabetes charity JDRF.

Wallace said she was surprised by the findings, and that the initial discovery that one in five genes showed seasonal variation was "enormous."

The study adds some new insight into why winter's so sucky, and it may hint at a few practical takeaways, such as treating diseases in accordance with the seasons. One suggestion, said Wallace, is that getting vaccines is more effective in winter, when the immune system is most primed to respond.

"You could think it might be better to vaccinate in the winter time, when the increased response to the vaccine would offer more protection than in the summertime," she said, though she noted that other things come into play: You don't want to wait until halfway through the flu season to get your jab as you'd still be vulnerable.

For now, enjoy the summer—the year's only going to get worse.