Effect of daily variation in weather and sleep on seasonal affective disorder.

Analysis of daily self-ratings of energy for 10 patients diagnosed with seasonal affective disorder (SAD) revealed statistically significant seasonal patterns in eight patients (with all patients showing the most energy in the summer and the least energy in the winter). When weather was controlled for, the seasonal patterns in energy persisted in seven of the eight patients. In a lesser number of subjects (four), there were significant effects of weather after controlling for season; however, when the effects of weather on energy were examined separately for each season, 8 of the 10 subjects were found to be influenced by weather in at least one season. Daily sleep data showed statistically significant seasonal patterns in all 10 patients (with 6 subjects showing maximum sleep in winter and 4 in summer). As for the relationship between energy and sleep, a loss of energy appeared to predict longer sleep on that night and the next night (7 of 10 patients), whereas there was no evidence that prolonged sleep influenced energy on the following and subsequent days.