Researchers from the Charité Hospital in Berlin have found out that adult city dwellers sleep for half an hour longer in winter. The findings were published in Frontiers in Neuroscience. The researchers studied data on 292 participants who were subjected to polysomnography - the study, where patients are asked to sleep in the usual way, without the alarm clock and the method monitors the quality, type and duration of sleep. All subjects were monitored at different times of the year to look at differences between months. Also excluded were volunteers who were taking medications that affect sleep, those with technical failures during polysomnography, and those with a fast sleep latency of more than 120 minutes (the first fast sleep episode was thought to have been missed). After group correction, 188 participants remained who lived in a city with low natural light and high light pollution. Most disorder diagnoses were not strongly associated with seasons, but insomnia was more frequently diagnosed toward the end of the year. Total sleep time was about an hour longer in winter than in summer, but this result was not statistically significant. However, REM sleep was 30 minutes longer in winter than in summer. Fast sleep is known to be directly related to circadian rhythms, which are affected by changes in light. Although the team notes that these results would need to be confirmed in a larger sample of participants who do not experience sleep problems, the seasonal changes may be even more pronounced among this group. The authors suggest that going to bed earlier in the winter may help adjust for seasonality. Authorities and employers should also consider adjusting school and work schedules to accommodate seasonal sleep needs.