The changes in temperature and daylight brought by winter may make a person feel like hibernating.
It turns out that humans do get longer REM sleep in wintertime and less deep sleep in autumn, even in an urban setting, German researchers reported Feb 17 in Frontiers in Neuroscience. REM sleep is the stage when vivid dreams occur; it is not the deepest sleep.
“Possibly one of the most precious achievements in human evolution is an almost invisibility of seasonality on the behavioral level,” said study author Dr. Dieter Kunz, who is based at the Clinic for Sleep and Chronomedicine at St. Hedwig Hospital in Berlin.
“In our study we show that human sleep architecture varies substantially across seasons in an adult population living in an urban environment," Kunz said in a journal news release.
It can be challenging to study how seasons affect sleep using objective measures.
To do this, a team at the Charité Medical University of Berlin recruited 292 patients who had undergone sleep studies called polysomnographies at various times.
The patients' sleep disorders could potentially affect results, but this made for a large study group evenly spread throughout the year.
Polysomnographies are done in a laboratory where quality, type and length of sleep can be monitored.
After excluding some patients, including those taking medications known to affect sleep, and those who apparently skipped the first nightly episode of REM sleep, they ended up with 188 participants.
Most of their diagnoses showed no seasonal pattern.
Patients were based in an urban environment with low natural light exposure and high light pollution, but researchers still found seasonal changes in sleep.
Total sleep time was about an hour longer in winter than in the summer. This result was not considered statistically significant.
REM sleep, the period when people tend to have vivid dreams, was 30 minutes longer in the winter than in summer.
Results will need to be validated in a group without sleep difficulties. Seasonal changes may be even greater in a healthy population, the researchers said.
Society might benefit from schedule accommodations that would allow humans to respond to changing seasons, researchers said. Going to sleep earlier in the winter could also help.
"Seasonality is ubiquitous in any living being on this planet,” Kunz said. “Even though we still perform unchanged, over the winter human physiology is down-regulated, with a sensation of ‘running-on-empty' in February or March. In general, societies need to adjust sleep habits including length and timing to season, or adjust school and working schedules to seasonal sleep needs."
The U.S. National Institute of Neurological Disorders and Stroke has more on sleep.
SOURCE: Frontiers in Neuroscience, news release, Feb. 17, 2023