A growing body of research in psychology and related fields suggests that winter brings some profound changes in how people think, feel and behave.
The natural and cultural changes that come with winter often occur simultaneously, making it challenging to tease apart the causes underlying these seasonal swings.
We recently conducted an extensive survey of these findings with research colleagues Alexandra Wormley, a social psychologist at Arizona State University, and Mark Schaller, a psychologist at the University of British Columbia.
Wintertime blues and a long winter’s nap
Do you find yourself feeling down in the winter months? You’re not alone. As the days grow shorter, the American Psychiatric Association estimates that about 5 percent of Americans will experience a form of depression known as seasonal affective disorder, or SAD.
People experiencing SAD tend to have feelings of hopelessness, decreased motivation to take part in activities they generally enjoy, and lethargy. Even those who don’t meet the clinical threshold for this disorder may see increases in anxiety and depressive symptoms.
Scientists link SAD and more general increases in depression in the winter to decreased exposure to sunlight, which leads to lower levels of the neurotransmitter serotonin. Consistent with the idea that sunlight plays a key role, SAD tends to be more common in more northern regions of the world, such as Scandinavia and Alaska, where the days are shortest and the winters longest.
Humans, special as we may be, are not unique in showing some of these seasonally linked changes. For instance, our primate relative the Rhesus macaque shows seasonal declines in mood.
Some scientists have noted that SAD shows many parallels to hibernation — the long snooze during which brown bears, ground squirrels and many other species turn down their metabolism and skip out on the worst of winter. The disorder may have its roots in adaptations that conserve energy at a time of year when food was typically scarce and when lower temperatures pose greater energetic demands on the body.
Cold weather weight gain
Winter is also well known as a time of year when many people put on a few extra pounds.
Research suggests that diets are at their worst and weight at its highest during the winter, and a recent review of studies found that average weight gains during the holiday season are about 1 to 3 pounds. People who are overweight or obese tend to gain more, the review showed.
There probably is more going on with year-end weight gain than just overindulgence in abundant holiday treats.
In our ancestral past, in many places, winter meant that food became more scarce. Wintertime reductions in exercise and increases in how much and what people eat may have been an evolutionary adaptation to this scarcity.
If the ancestors who had these reactions to colder, winter environments were at an advantage, evolutionary processes would make sure the adaptations were passed on to their descendants, coded into our genes.
Sex, generosity and focus
Beyond these winter-related shifts in mood and waistlines, the season brings with it a number of other changes in how people think and interact with others.
One less discussed seasonal effect is that people seem to get friskier in the winter months. Researchers know this from analyses of condom sales, sexually transmitted disease rates and internet searches for pornography and prostitution, all of which show biannual cycles peaking in the late summer and the winter months.
Data on birthrates also shows that in the United States and other countries in the Northern Hemisphere, babies are more likely to be conceived in the winter months than at other times of the year.
Although this phenomenon is widely observed, the reason for its existence is unclear. Researchers have suggested many explanations, including health advantages for infants born in late summer, when food may historically have been more plentiful, changes in sex hormones altering libido, desires for intimacy motivated by the holiday season, and simply increased opportunities to engage in sex.
But winter boosts more than sex drive. Studies find that during this time of year, people may have an easier time paying attention at school or work.
Neuroscientists in Belgium found that performance on tasks measuring sustained attention was best near the winter and summer solstices.
And there may also be a kernel of truth to the idea of a generous Christmas spirit.
In countries where the holiday is widely celebrated, rates of charitable giving tend to show a sizable increase around this time of year. And people become more generous tippers, leaving about 4 percent more for waitstaff during the holiday season. This tendency is probably a response to the altruistic values associated with winter holidays that encourage behaviors like generosity.
Like many other animals, we are seasonal creatures.
In the winter, people tend to eat more, move less and mate more. You may feel a bit more glum, while also being kinder to others and having an easier time paying attention. As psychologists and other scientists research these kinds of seasonal effects, it may turn out that the ones we know about so far are only the tip of the iceberg.
Michael Varnum is an associate professor of psychology at Arizona State University. Ian Holm is a graduate student of psychology at the University of British Columbia. This article was produced in collaboration with the Conversation, a nonprofit news organization.
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December 12, 2023 at 06:09PM
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