The research, which was carried out by scientists at the University of Copenhagen in Denmark, found that people who suffer from SAD experience production of a transporter protein in the brain as night draws in. This lowers the production of serotonin, making SAD patients feel depressed.
The Danish researchers made that discovery by studying the brains of 34 people, 11 having SAD. They used positron emission topography (or PET) brain scans which revealed significant differences between summer and winter serotonin levels among SAD patients.
The discovery of the transporter protein (or SERT) that causes serotonin levels to drop off during winter is considered very important. “We believe that we have found the dial the brain turns when it has to adjust serotonin to the changing seasons,” noted the study’s lead researcher, Dr. Brenda McMahon. “Sunlight keeps this setting naturally low, but when the nights grow longer during the autumn, the SERT levels increase, resulting in diminishing active serotonin levels.”
Other researchers, like mental health expert Sam Challis, agree that this is an important discovery but want to see research expanded to include more participants. “We don’t yet know enough about how serotonin levels can be affected by light levels so this is quite an interesting, albeit small, study,” noted Challis, who works for mental health charity Mind. “We would welcome more research.”
It’s estimated that about two million residents of the United Kingdom deal with SAD.
