Impact of seasons and temperatures on the sleep-wake cycle in a French elderly rural population

Sleep is known to be affected by season changes in a temperate climate. Temperature changes are known to affect sleep directly, but in this context, season-related changes in the circadian rhythm may play an important role as well. The objectives of this study were to verify the effect of season and temperature on sleep parameters of elderly French subjects and to focus on the sleep-wake cycle. Sleep parameters and sleep-wake cycle parameters were analyzed through actigraphy while seasonality and temperature were acquired from recording dates and weather records from online scientific archives. ANOVAs were carried out to investigate the effect of seasons on actigraphic parameters and to calculate regression models for temperature. A sample of 157 subjects (49.7 % women) participated in the study with a mean age of 76.9 ± 4.5 years. Inter-daily stability of the sleep-wake cycle was higher in autumn and winter with a higher mean activity during those months. Time in bed was significantly longer in autumn and winter while there was a similar trend for total sleep time. Those variables changing with the seasons were negatively linked to ambient temperature. Not only sleep but also the sleep-wake cycle is impacted by seasonal changes in elderly French subjects. Seasons should be taken into consideration when planning sleep-wake cycle recordings in temperate climates, in particular for longitudinal protocols. Clinical interventions should take season-related sleep-wake cycle problems into account, particularly in the elderly, who suffer more often from sleep disorders than other age groups. Since elderly also suffer more from climate change effects, this study further adds to the demand for clinical monitoring and housing adaptations for the elderly in the future.