Seasonal sleeping: Why we need more rest in the winter

Going to sleep earlier in the winter might help accommodate human seasonality.

ISLAMABAD, (ONLINE) - A study published today in the journal Frontiers in Neuroscience reports that humans experience longer REM sleep in winter than summer – even in artificially lit urban areas – and less deep sleep in autumn.

Researchers from Charité Medical University of Berlin said human body clocks are set by the sun and changing day length and light exposure over the course of the year can affect our sleep duration and quality.

“Possibly one of the most precious achievements in human evolution is an almost invisibility of seasonality on the behavioral level,” said Dr. Dieter Kunz, a clinical psychiatrist, sleep researcher, and clinical chronobiologist at the Clinic of Sleep & Chronomedicine at the St Hedwig Hospital, Berlin, who authored the study.

“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 statement.

How the human sleep study was conducted

The research team recruited 292 participants to undergo sleep studies called polysomnographies, which are done with people experiencing sleep-related difficulties.

The participants went to a special laboratory where they were asked to sleep naturally, without an alarm, where the quality, type, and length of sleep can be monitored.

Researchers acknowledged sleep disorders could potentially affect the results, but the study conditions allow for a large group to be evenly spread throughout the year to better demonstrate month-to-month differences.

The study excluded people taking medications known to affect sleep, those experiencing technical failures during the polysomnography, and REM sleep latency longer than 120 minutes, which suggested that the first REM sleep episode had been skipped.

The exclusions left 188 subjects remaining. Most of their diagnoses showed no seasonal pattern, but insomnia was more commonly diagnosed toward the end of the year.

Seasonal sleeping explored

Researchers said, despite subjects being based in an urban environment with low natural light exposure and high light pollution – which they said should affect any seasonality regulated by light – the scientists found “subtle but striking changes across the seasons.”

Although total sleep time was about an hour longer in the winter than in summer, the researchers said that wasn’t statistically significant. However, the participants experienced 30 more minutes of REM sleep during winter than in summer. REM sleep is directly linked to the circadian clock, which is affected by changing light.

The team acknowledged the results need to be validated in a population experiencing no sleep difficulties, but they said the seasonal changes could be even greater in a healthy population.

The researchers added that although most people’s waking time is usually out of their control, due to school or work schedules, society could benefit from accommodations allowing people to respond more effectively to the changing seasons.

Until then, they said going to sleep earlier in the winter might help accommodate human seasonality.

“Seasonality is ubiquitous in any living being on this planet,” said Kunz. “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.”

How light affects sleep

Robert Soler is a former NASA engineer who studied how lack of light in space impacted astronauts’ sleep cycles. He’s also the co-founder of BIOS Lighting.

Soler told Healthline that not only is the amount of light our bodies tied to the amount of sunlight present, it’s also about the type of light we get.

“The sun cycles through sunrise, daytime, sunset, (and) nighttime light, which all have different colors that our body interprets as stimuli for different energy levels and activities,” Soler said. “Bluer light in the morning – like a morning sky – gives a boost of energy and helps get you to get out of bed. Daytime light, or bright light, with cooler tones help signal to your body that it’s time to be alert and help with productivity.

Then at the end of the day, the amber colors of a sunset prepare you for sleep.”

Soler noted that during winter the entire solar cycle is condensed and there are more hours of nighttime or darkness. As a result, not only does the darkness make us want to sleep more, but there are fewer hours of daytime light limiting how alert we are.

It’s not just city light versus rural light. It’s also about where you are on the globe.

“If the city you reside in is closer to the equator, your winters may be slightly brighter than others, so it’s possible your sleep schedule may not change much,” Soler said. “The amount of light pollution in your area could also affect your circadian rhythm. Why sleep matters

Soler added that how we sleep is more important than most people think.

“We all understand that we need sleep to function and be productive, but there are so many more nuances to it than that,” he said. “Our circadian rhythms help guide our sleep patterns, but it also determines our alertness and productivity, too. If you’re not getting enough sleep, or not enough good sleep, you’re directly impacting your daily life and potentially your general health and well-being. Mental health, metabolic health, and cardiovascular health are all tied to sleep.”

Jamie Evan Bichelman is a clinical psychologist and a lifelong survivor of major depression, including seasonal affective disorder (SAD). Bichelman told Healthline poorer sleep during winter months “traps us in a vicious cycle of requiring more sleep to compensate for the lack of quality rest the night before.”

“The production of melatonin is out of whack as we take in less natural sunlight, thereby disrupting the body’s natural processes that keep our sleep schedules stable,” Bichelman said. “Many individuals who suffer from seasonal depression utilize artificial light-making ‘SAD lamps’ to varying degrees of effectiveness.”

Bichelman noted that the problem with artificial lighting is too many companies make false claims.

“The market (is) being flooded with lamps with false claims, all in the name of marketing,” Bichelman said. “While medically reviewed data does suggest that SAD lamps can aid in regulating our body’s internal processes, unfortunately, many consumers fall victim to cheaply-made knock-offs.”

Bichelman said colder climates also have an effect.

“(Those) who must run the heat all winter long to live comfortably, the excess heat and lessening moisture in the air contribute to poor quality sleep, as we know from research that bodies require a certain degree of cold to more comfortably sleep,” Bichelman said.

He said poor sleep also affects our nutritional choices which, in turn, can affect sleep.

“Further trapping us in this vicious cycle is that as poor sleep adds up, we’re more inclined to make less nutritious decisions and turn to food that is quickly made and often less nutrient-dense,” Bichelman told Healthline. “The problem here is that these kinds of foods, when eaten with increasing frequency, likewise impact our quality of sleep and desire to sleep more often.”