Does late sleep promote depression?

It has long been known that jetlag has detrimental - although usually transient - effects on cognitive functions and mood. A recent study by Levandovski et al. now shows that a more chronic version of temporal misalignment, so-called social jetlag, is associated with higher depression scores in rural populations. In a cross-sectional study on a well-defined cohort of ethnically homogenous Brazilian immigrants, the authors found that desynchrony between sleep-wake rhythms and internal circadian time was correlated with higher depression scores. These data suggest that sleep timing has a stronger impact on mood and well-being than previously thought and could be used as a predictor of depression risk.