Whether we’re night owls or morning larks, our body clocks are set by the sun.
Theoretically, changing day length and light exposure over the course of the year could affect the duration and quality of our sleep.
But figuring out how this applies in practice is difficult.
Although studies, where people assess their own sleep, have suggested an increase in sleep duration during winter, objective measures are needed to determine how exactly the seasons affect sleep.
In a study from the Charité Medical University of Berlin, scientists found that even in an urban population experiencing disrupted sleep, humans experience longer REM sleep in winter than in summer and less deep sleep in autumn.
This suggests that human sleep architecture varies substantially across seasons.
In the study, the team examined 292 patients that had undergone sleep studies.
These studies are regularly carried out on patients who experience sleep-related difficulties, using a special laboratory where patients are asked to sleep naturally without an alarm clock, and the quality and type of sleep can be monitored as well as the length of sleep.
Although sleep disorders could potentially affect the results, this makes for a large study group evenly spread throughout the year, allowing for the investigation of month-to-month differences.
Even though the patients were based in an urban environment with low natural light exposure and high light pollution, which should affect any seasonality regulated by light, the scientists found subtle but striking changes across the seasons.
Although total sleep time appeared to be about an hour longer in the winter than the summer, this result was not statistically significant. However, REM sleep was 30 minutes longer in the winter than in summer.
REM sleep is known to be directly linked to the circadian clock, which is affected by changing light.
Although the team acknowledged that these results would need to be validated in a population that experiences no sleep difficulties, the seasonal changes may be even greater in a healthy population.
The team says although most people’s waking time is currently largely out of their control, due to school or work schedules, society might benefit from accommodations that would allow humans to respond more effectively to the changing seasons.
In the meantime, going to sleep earlier in the winter might help accommodate human seasonality.
If you care about sleep, please read studies about exercise that can help you sleep better, and this new drug could reduce symptoms of sleep apnea.
For more information about health, please see recent studies that black tea may strongly reduce blood pressure, and results showing these high blood pressure drugs may increase heart failure risk.
The study was conducted by Dr. Dieter Kunz et al and published in Frontiers in Neuroscience.
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