For many, shorter winter days and gloomy weather bring about low energy and a desire to hibernate inside. But for some 6 to 14% of Americans, less sunlight and time outside leads to a form of clinical depression known as seasonal affective disorder (SAD).

“The human body has a significant connection with its surroundings, including the change of season, the amount of light from the sun, and the atmospheric pressure,” Spencer Kroll, MD, Ph.D., an internal medicine specialist at Kroll Medical Group in New Jersey, told Insider.  

Two neurotransmitters, serotonin and melatonin, help maintain the body’s daily sleep-wake cycles (part of our circadian rhythms) but they’re also significantly affected by sunlight. In people with SAD, shorter winter days can change serotonin and melatonin levels. That, in turn, disrupts your sleep and can lead to both depression and insomnia. 

Luckily, there are a number of products and strategies widely used for at-home seasonal affective disorder treatment, like a light therapy lamp, often called a “happy lamp.” Other treatments, however, such as cognitive-behavioral therapy and medications, require a professional.