It’s chilly outside, and the days are getting shorter. Do you dread winter because you get the blues? If you had the blues or felt depressed the past two winters but feel better in the spring and summer, you may have seasonal affective disorder, or SAD, a type of depression that occurs during the same season each year.

Can SAD be prevented?

Because the onset of winter is predictable, people with a history of SAD might benefit from starting treatments before the fall season to help prevent or reduce depression. Regular exercise is one of the best things you can do for yourself. If the sun is shining, try to get outside. Being active, especially early in the day, may help you have more energy and feel less depressed. Symptoms come and go at roughly the same times every year, which is an easy way to track when it’s time to add to your physical activity.

What causes SAD

Scientists don’t fully understand what causes SAD, but research indicates it might be from reduced activity of the brain chemical serotonin, which helps regulate mood. Research also suggests that sunlight controls the levels of molecules that help maintain normal serotonin levels. In people with SAD, this regulation does not function properly, resulting in lower serotonin levels in the winter.

Other findings suggest that people with SAD produce too much melatonin, a hormone that is essential for maintaining the normal sleep-wake cycle. In people with SAD, the changes in serotonin and melatonin levels disrupt normal daily rhythms. As a result, they can no longer adjust to the seasonal changes in day length, leading to sleep, mood and behavior changes.

Vitamin D is believed to promote serotonin activity. Few foods in nature provide vitamin D, but it’s in egg yolks and canned fish. The body produces vitamin D when exposed to sunlight on the skin. With less daylight in the winter, people with SAD may have lower vitamin D levels.

Who gets SAD

Millions of adults may suffer from SAD, although many might not know they have the condition. SAD occurs more often in women, and it is more common in those living farther north, where there are shorter daylight hours in the winter. It’s most common in people between the ages of 15 and 55, and the risk of getting SAD for the first time goes down as you age. In most cases, SAD begins in young adulthood and sometimes runs in families.

Treatments are available that can help many people with SAD. Talk to your healthcare provider about which treatment is best for you.