In the West, seasonal affective disorder (SAD) is mostly a winter phenomenon. But two studies reveal that in other locales, that's not necessarily the case.
Wintertime depression has been linked to melatonin, a hormone we naturally release when darkness falls, which makes us sleepy. Some scientists believe that as day length wanes, melatonin secretion increases, causing the lethargy linked with SAD. It would follow that SAD would be pervasive in Iceland, where there is very low light during the winter. But a study published in the American Journal of Psychiatry showed no evidence of seasonal mood change among Icelanders. The near absence of winter depression was likely caused by a genetic selection process favoring "those who had full stamina during the winter" and could survive the plagues, volcanoes and ice that have pummeled Iceland over the past millennium, says Hogni Oskarsson, M.D., a psychiatrist at Ulleval Hospital in Oslo, Norway.
