A study involving people who suffer from seasonal affective disorder or SAD might have uncovered the secret why some are resilient to developing depression.

The Winter Blues

SAD is a type of depression that only happens around the late fall and early winter. It, however, goes away as soon as spring and summer begin.

While seasonal depression can also occur during the summer season, it is considered a lot less common than winter episodes. That is why SAD is also sometimes referred to "winter blues."

According to the National Institute of Mental Health, the symptoms of SAD include low energy, hypersomnia, overeating, weight gain, intense craving for carbohydrates, and social withdrawal.

About 5 percent of the population in the United States experience SAD. The mental disorder is also typically diagnosed in women, accounting for 4 out of 5 of cases.

Albeit triggered by seasonal change, people with a family history of other types of depression are more at risk of developing SAD.

SAD And Depression

The study published by the journal European Neuropsychopharmacology looked at the people who are genetically prone to developing SAD but resist the environmental factors that trigger it. By looking at the neurobiology of SAD, researchers hoped to understand why some people are more resilient to depression.

Previous research has identified that the gene 5-HTTLPR, which encodes the cerebral serotonin transporter in the brain, is found in people who have SAD. Cerebral serotonin transporter regulates how efficiently the serotonin is removed from the brain.

Antidepressants target the cerebral serotonin transporters in order to slow down the removal of serotonin (a.k.a. happiness neurotransmitter) from the brain.

The recent study found that people who are genetically likely to have SAD but were resilient to the condition downregulated levels of cerebral serotonin during the winter time.

"We found that some people who you would expect to have SAD because of their genetic disposition were nevertheless able to control how much serotonin transporter was produced, which means that they were able to regulate how much serotonin was removed from their brain," explained Brenda McMahon, one of the authors of the study. "[In] this way, they become more resilient to depression."

The study involved 23 people, 13 of who were women who have the gene 5-HTTLPR but have not developed SAD. The researchers used a positron emission tomography scanner to track the levels of cerebral serotonin transporter and serotonin of the participants once during summer and twice during winter.

The researchers hope that their findings will lead to the treatment of SAD with selective serotonin reuptake inhibitors.