Sleep biomarkers of seasonal vulnerability in major depressive episodes: a clinical study using actigraphy and polysomnography

Seasonal affective disorder or major depressive episode (MDE) with winter seasonal pattern is a severe form of recurrent depressive disorder persisting for at least 40 % of the year. This seasonal vulnerability may involve specific chronobiological and sleep regulation disturbances, however, actigraphy and polysomnography studies reported conflicting and inconclusive findings. In this context, we hypothesized that individuals with MDE who exhibit higher vulnerability to seasonal changes display distinct chronobiological and sleep regulation disturbances. We investigated how sleep and circadian rhythms, assessed through subjective markers (<i>N</i> = 254) and objective actigraphic (<i>N</i> = 96) and polysomnographic markers (<i>N</i> = 54)-varied in individuals with MDE according to their vulnerability to seasonal changes. To conduct this dimensional approach, that may be closer to the pathophysiology, we assessed the seasonal vulnerability using the Global Seasonality Score (GSS) from the Seasonal Patterns Assessment Questionnaire (SPAQ). The results revealed that greater seasonal vulnerability was correlated to increased excessive daytime sleepiness (Epworth scale), (<i>r</i> = 0.218, <i>p</i> < 0.001), shorter REM sleep latency (<i>r</i> = -0.381, <i>p</i> = 0.005), (even when controlling for age using the Kupfer index (<i>r</i> = -0.452, <i>p</i> < 0.001)), and shorter N1 sleep latency (<i>r</i> = -0.411, <i>p</i> = 0.002). The regression model retained only the polysomnographic markers-N1 sleep latency, REM sleep latency, Kupfer Index-independently and significantly associated to the GSS. This study confirms a link between seasonal vulnerability and shortened REM sleep latency, emphasizing that light and the photoperiod play a pivotal role in regulating the systems involved in REM sleep dysregulation in depressive disorders.