A new study used a model of seasonal affective disorder to find out why some people don’t develop depression despite being genetically predisposed to it. The findings also shed light on potential new treatments for seasonal depression.

girl looking out the window

Seasonal depression affects about 5 percent of the U.S.

The National Institute of Mental Health estimate that over 16 million people in the United States, or 6.7 percent of the population, will have had more than one episode of major depression during the past year.

A further 5 percent live with seasonal affective disorder (SAD), or seasonal depression.

The symptoms of SAD are so similiar to those of depression that it can sometimes be hard to distinguish between the two.

SAD, also known as winter blues, typically affects women. In fact, 4 in 5 people with the condition are women, and the reasons for this predisposition are likely to be genetic.

However, while some people are genetically prone to the condition, they resist the environmental factors that might trigger it.

So, new research set out to examine the neurobiology of SAD in an attempt to understand what it actually is that makes some people more resilient to developing depression.

The new study was led by Dr. Brenda McMahon, of Rigshospitalet in Copenhagen, Denmark, and the findings were published in the journal European Neuropsychopharmacology.

The key role of serotonin transporters

As Dr. McMahon and her colleagues explain, seasonal depression is caused by insufficient daylight, making the condition more widespread in countries that are farther from the Equator.

She says, “Daylight is effectively a natural antidepressant. Like many drugs currently used against depression, more daylight prevents serotonin [from] being removed from the brain.”