If you’re prone to feeling down during the wintertime, you’re not alone. Seasonal affective disorder (SAD) is a type of depression triggered by the change in seasons, and it affects between 4% and 6% of people in the United States, according to the American Academy of Family Physicians. Although most people with SAD are affected primarily in the winter months, some cases can occur during the spring and summer.
There are many theories about what leads some people to develop SAD, although experts have yet to pinpoint a cause. Some experts believe that seasonal changes disrupt the circadian rhythm. Others think that hormones that regulate sleep and mood, such as melatonin and serotonin, are disrupted by the changing seasons.