Seasonal mood disorder (SMD) is likely prevalent among children and adolescents; however, there are few empirical investigations of pediatric SMD in the literature. To contribute to the field, the current study investigates the seasonality of mood and behavior among children and adolescents using longitudinal data collected from 1987 to 1998. One hundred eleven youths diagnosed with depression, 369 bereaved youths, 129 community controls, and their parents completed individual assessments at baseline, five, thirteen, and twenty-five months later. Assessment materials include several measures of depressive symptoms and diagnostic instruments. Multilevel analyses were conducted using MlwiN software.
According to both parent- and child-report, youths from all three groups earn significantly higher total scores on measures of depression during the winter than the summer. On the other hand, significant seasonal effects do not arise for a measure of overall psychopathology. This implies that seasonality is limited to mood disorders. While this seasonal effect is significant, actual changes of mean scores on measures of depression from the summer to the winter are minimal, suggesting that season may have little affect on the mood and behavior for the majority of participants from each group. It is uncertain whether a few highly seasonal participants influence the mean changes between summer and winter or whether each group as a whole experiences very mild seasonal changes. In either case, the finding that depressed, bereaved, and community controls show similar average levels of seasonality supports the dual vulnerability model of SMD, which posits that seasonality and propensity toward depression are independent.
Data collected from the youths, themselves, suggest that seasonality shown on measures of depression arise from seasonal changes in atypical vegetative symptoms as opposed to cognitive or affective symptoms. This is consistent with the hypotheses. However, data collected from their parents do not show an association between season and any particular depressive symptom cluster. Therefore, it is unclear whether seasonality of depression is attributable to the characteristics uniquely associated with SMD; namely, atypical vegetative symptoms. Overall, the current study provides useful information for understanding seasonality in mood and behavior among children and adolescents.