Dec. 5, 2002 -- A sunny day may do more than just boost your mood -- it may increase levels of a natural antidepressant in the brain. A new study shows that the brain produces more of the mood-lifting chemical serotonin on sunny days than on darker days.
Researchers say the findings provide more evidence that lack of sunlight and reduced serotonin levels are important in the development of seasonal affective disorder (SAD).
People with SAD develop symptoms of depression in the winter months when there is less daylight. Symptoms include difficulty concentrating, low energy or fatigue, loss of interest in daily activities, moodiness, and sleeping excessive amounts.
Serotonin levels have been found to be normal in previous studies of people with SAD. But researchers say those studies looked at serotonin levels in the fluid that circulates around the brain and spine, which may have interfered with their results.
In the current study, researchers measured serotonin levels in the blood vessels leading directly from the brain -- a more accurate measure of serotonin levels, they say. The study, by Gavin Lambert of the Baker Research Institute in Melbourne, Australia, and colleagues, appears in the Dec. 7 issue of The Lancet.
Samples were taken from 101 healthy men during each of the four seasons and compared with various weather factors, such as temperature, rainfall, hours of bright sunlight, and atmospheric pressure.
Researchers found that regardless of the season, the turnover of serotonin in the brain was affected by the amount of sunlight on any given day. And the levels of serotonin were higher on bright days than on overcast or cloudy ones. In fact, the rate of serotonin production in the brain was directly related to the duration of bright sunlight.
No other atmospheric conditions were related to serotonin levels.
The researchers say their study shows that the prevailing amount of sunlight clearly affects serotonin levels in healthy individuals, but more research is needed to see if people predisposed to SAD are affected in the same way by environmental factors.