Circadian rest-activity disturbances in children with seasonal affective disorder

Seasonal affective disorder (SAD) affects from 1.7% to 5.5% of children. Previous studies found that nonseasonally depressed children had a blunted circadian rhythm, while adults with SAD had a delayed and poorly entrained rhythm. The purpose of this study was to determine whether pediatric SAD more closely resembles nonseasonal pediatric depression or adult SAD.

Twelve normal, healthy volunteers (11.6 +/- 3.7 years; 6 female, 6 male) and 14 unmedicated children with SAD (11.0 +/- 3.3 years; 9 female, 5 male) meeting Rosenthal/NIMH criteria for SAD and Schedule for Affective Disorders and Schizophrenia for School-Age Children-Epidemiologic version criteria for major depression had their levels of activity recorded for 72 hours (weekdays) using belt-worn actigraphs.

The SAD group had blunted circadian amplitudes that were 10% lower than normal (p = .004). They were more poorly modeled by the standard cosinor equation (p = .001), and a circadian rhythm accounted for 39% less of the variability in their activity profile (p = .007). The amplitude of the 12-hour harmonic rhythm was markedly increased. There were no differences between SAD and control children in the timing of the circadian rhythm and degree of entrainment.

Children with SAD displayed dysregulated circadian activity rhythms comparable with those reported in nonseasonally depressed children, yet different from those observed in adults.