Working night shifts and sleeping on a schedule that is out of whack with your body’s natural rhythms has been associated with obesity and type 2 diabetes. Now a new study that subjected participants to three weeks of disrupted, short sleep sessions is helping to tease out just how those problems may arise.
Researchers at Brigham and Women’s Hospital carefully monitored 21 healthy people who lived in a laboratory where their sleep schedules were tweaked, moved from normal night-time sleeping to five-and-a-half-hour spurts of sleep, spread out at all times of day and night. In the study, published Wednesday in the journal Science Translational Medicine, the scientists reported that the disrupted schedules altered insulin levels and sent three people into a pre-diabetic state. The irregular, restricted sleep schedule also slowed metabolism to a rate that, if sustained over an entire year with no other changes in the person’s routine and diet, would amount to more than 12 pounds of weight gain.
“Getting adequate sleep is what we’re calling one of the three pillars of health: sleep, diet, and exercise go well together, and they interact,” said Orfeu Buxton, assistant professor of medicine at Harvard Medical School and a neuroscientist at the Brigham, who led the research. “If you don’t get enough sleep, it’s hard to get enough exercise. If you’re not getting enough sleep, people eat more food. That causes them to gain weight and make inappropriate food choices -- sugary treats and snacks.”
The study adds to the growing body of evidence that shortened sleep or sleeping at odd times is associated with negative health effects. A study published last year reported that among 175,000 nurses studied, those who worked night shifts three or more times a month, for more than two years, were at increased risk for type 2 diabetes. The new paper suggests one possible mechanism that could account for that difference, and scientists now plan to study the biology in further detail, to understand exactly why a disrupted or shortened sleep schedule sends insulin levels off-kilter. They also plan to look for prevention strategies
Buxton said people need to start thinking of sleep differently. After this study, he quit taking red-eye flights. He suggested that people determine their “number” -- the number of hours they naturally need to sleep, which for most people will be between seven and nine hours each night. To determine what that number is, he said, follow a series of simple steps: don’t ingest caffeine or other stimulants, catch up on a sleep debt, and then go to sleep without an alarm clock. People will find that, within about 10 minutes margin of error, they need the same amount of sleep every night.
Buxton said he found out his number -- 7 and 3/4 hours -- when he was in college, long before he began to study sleep. Violating his normal sleep schedule causes him to function less well overall -- a fact that he learned by failing an 8 a.m. honors organic chemistry class.
When sleeping at odd hours can’t be avoided, he said, people should do their best to shift their body clock so that they are sleeping and eating when their body thinks those activities should take place. That could mean working night shifts consistently for a month, instead of rotating to take night shifts for a few days a week. He also cautioned against “social jet lag” in which people sleep in on the weekends to make up for a sleep debt. Two days, he said, may not be enough time.
Kathryn Reid, a research assistant professor of neurology at the Feinberg School of Medicine at Northwestern University, who was not involved in the study, said she was surprised that the age of the participants, half of whom were in their 20s and half of whom were in their late 50s or early 60s, did not seem to make a difference in how people’s health was affected by sleep.
Reid said that might be because the people in the study were healthy, while many people who experience shortened and disrupted sleep are shift workers with underlying health problems. Future questions, she said, will be to understand the health effects of disrupted sleep on that population and to learn what interventions might help metabolism bounce back more effectively.