The holidays are billed as a time of joy, but they can also be a time of increased stress for many people. In addition, Wednesday, Dec. 21, is the winter solstice—the shortest day of the year, with the sun setting in Boston at the early hour of 4:15 p.m. Seasonal affective disorder, or SAD, is a form of major depression that often strikes in these shorter, darker days.

We asked Lisa Feldman Barrett, University Distinguished Professor of Psychology at Northeastern, why the holidays affect so many of us this way and what we can do to minimize the difficult emotions we may experience.

We generally attribute increased stress to external sources: We feel we have too much to do, or the season reminds us of past losses and what is missing in our lives today. However, in your forthcoming book, How Emotions Are Made: The Secret Life of the Brain, you posit a theory that says we “construct” instances of stress because of how our brains work. What does that mean?

Just as a large company has a financial office that parses its revenues and expenses to develop budgets for various accounts, you, too, have a “financial office”—your brain. While your brain creates thoughts, feelings, and perceptions, it also manages the budget for all the accounts in your body, for example, nutrients such as water, salt, and glucose, a simple sugar that is our cells’ primary energy source. There’s a technical term for keeping these accounts in balance: allostasis. At certain times, say, when you exercise, your muscles may need more glucose than your digestive system, and it is the brain’s job to divvy up the resources appropriately to keep the balance. If you exercise for long enough, then the brain may use up more nutrients than is comfortable, and you’ll lose that balance.  Your brain will then correct it once you step off the treadmill by, perhaps, cuing you to eat a snack.

Even on the grayest day, you can find something that will inspire a sense of beauty or awe.
— Lisa Feldman Barrett, University Distinguished Professor of Psychology

For the brain to manage your body’s budget efficiently, it must be able to predict what your body will need so the resources will meet the need before it arises. For example, if your brain is preparing you for a sprint, it will increase your blood pressure and move glucose into your muscles before the action starts so you can, literally, hit the ground running. Overall, your brain is very good at its budget-balancing task.

Stress results when the balance goes off kilter and the body is taxed. Now, there is “good” stress, like that experienced in the exercise example above. You have a moment of imbalance for the greater good (exercise benefits your heart, brain, and other organs) that you can quickly correct, here with a snack and some water. However, if your brain is constantly preparing your body to deal with a threat that never materializes, the imbalance—the stress—becomes chronic: You feel as if you are carrying the weight of the world on your shoulders. The sensations translate as affect (feeling pleasant or unpleasant, feeling activated or calm), which is a raw ingredient of emotions: You experience fatigue, depression, anxiety, guilt, shame, disgust, and agitation.

Why does our stress often increase during the holiday season?

We are a social species. Unbeknownst to us, we regulate each others’ nervous systems all the time: through smell, touch, sounds, and vision, and even through the words we speak to one another. Indeed, the systems in the brain that are important for language connect directly to circuitry that regulates our body budget. That means other people can help balance that body budget or, conversely, send it off course. Either may happen more frequently during the holidays because we are surrounded by others so often.

There is a Dutch word, gezellig, that can be translated to mean cozy, nice atmosphere, a sense of belonging, time spent with loved ones. That is the positive side of being with other people—you feel a synchrony, your loved ones contribute to your allostasis.  Their body budgets are helping yours and vice versa. If you spend too much time alone, during the holidays or at other times, your body budget suffers because your brain is trying to manage it all on its own. There’s another negative side, too, which can be characterized by the English word angst: annoying family members, large parties where you know very few guests, that hole in the gut when you’re reminded of someone you lost. It can send your blood pressure soaring, your throat constricting.

What are some ways we can counteract stress during the holidays?

There are several lifestyle choices that ease your brain’s job of managing your body budget.

Get enough sleep. Different people need different amounts of sleep, but seven to eight hours is the standard recommendation. Lack of sleep is one of the great body-budget de-regulators. It throws off your body’s circadian rhythm, the normal rise and fall of the hormones that wake you up and wind you down.

Exercise in a way that suits you. If you love to run, going out for a jog may be a great de-stressor, but if you don’t, it may have the opposite effect. Figure out what form of exercise makes you feel good. You might choose to go for a restorative swim, or for a leisurely walk in a park or around the block, working to stay present in the moment by paying attention to details in the world around you. If you have the time and resources, consider a massage or yoga sessions. Massage can be extremely helpful because it is known to stimulate the opioids in the skin and reduce inflammation in the body. A gentle massage—a friend rubbing your shoulders—could be just as effective as a deep tissue massage.

Eat healthfully. High-fat, high-sugar, highly processed carbohydrates are delicious and may feel like comfort food but they actually work against keeping your body budget in balance over the long term. Be sure you are eating salads, fruits and vegetables, lean protein, and whole grains.

What role does light play in the development of seasonal affective disorder?

The retina, a part of the brain, is a layer at the back of the eye that converts light energy into nerve signals, enabling you to see. Ganglion cells in the retina not only receive visual information; they also regulate your circadian rhythm, which, as mentioned above, is the cyclical rise and fall of hormones that in turn wake you up and make you sleepy. A disruption in your circadian rhythm knocks your body budget for a loop.

The lack of light is one factor that can tax your body budget, leading to a state of depression. Many other factors can contribute as well, including a genetic predisposition and trauma. In severe depression, the brain may stop processing information correctly from the outside world, leading to faulty predictions regarding needs and, in turn, extreme energy deficits.

What are some ways we can counteract depression during these darker days?

We go outside less when it’s dark, are more sedentary, and may sleep too much, again throwing off our circadian rhythm. In addition, because we stay inside more, we often don’t get enough vitamin D; our bodies require sunlight to produce vitamin D. A vitamin D deficiency can upset your body budget, as it interferes with your thyroid and other functions.

All of this points to making sure that you spend time outdoors, in natural light—try for a walk every day, if possible. Nothing replaces being out in the light. Even when it’s cloudy, the sun’s rays get through. While walking, cultivate an appreciation for what you see, hear, smell, touch. Even on the grayest day, you can find something that will inspire a sense of beauty or awe. And that’s what the holiday season is supposed to be about.