But it's very real. Jackie now spends the entire summer on antidepressants, but before she got treatment her summer depression was so bad that she was at times suicidal. Come fall, though, her mood is just fine. She's just wired the other way. Since the late 1980s, mental health experts have known that the shorter days of fall and winter can bring on the blues.
Studies show that winter depression is caused by a dearth of daylight.
Summer depression, on the other hand, seems more closely tied to heat and humidity than to light. In Maryland, where researchers at the National Institute of Mental Health have been studying SAD for more than a decade, there's one documented case of summer depression for every five cases of winter blues. NIMH experts say that summer number gets bigger in areas with warmer climates. Dr. Thomas Wehr, who heads up the NIMH biorhythms division, says countries that are closer to the equator have higher rates of summer depression. In India, for example, summer SAD is far more common than the winter variety.