UC Davis

BACKGROUND: There is evidence that seasonal variation in depressive symptoms is common in the population. However, research is limited by a reliance on longterm retrospective methods. METHODS: Seasonal patterns were tested in two samples of community participants recruited in separate prospective studies in the Midwestern (n=556 males/females) and Pacific Northwestern (n=206 males) United States. Participants completed self-report measures of depressive symptoms 10-19 times from ages 14 to 36 years (n=8316 person observations). These data were compared with local meteorological conditions (e.g., solar radiation) recorded across the 2 weeks prior to each self-report. RESULTS: In within-subjects analyses, participants depressive symptoms and the probability of clinically significant symptoms varied with the time of year, as hypothesized (highest in the weeks of early Winter; lowest in early Fall). However, effect sizes were modest and were not explained by recent sunlight or other meteorological conditions. LIMITATIONS: Samples were not nationally representative. Participants did not complete retrospective reports of seasonal depression or measures of current vegetative symptoms. CONCLUSIONS: Neither time of the year nor recent seasonally linked meteorological conditions were powerful influences on depressive symptoms experienced by community populations in relevant geographic regions. Prior studies may have overestimated the prevalence and significance of seasonal variation in depressive symptoms for the general population.