Six weeks of shorter sleep increases weight and sedentary time

People who shortened their sleep by around 80 minutes a night for six weeks gained weight-one pound on average-and were more sedentary, researchers at Columbia University Vagelos College of Physicians and Surgeons have found.

"Our study shows that getting adequate sleep may help reduce the risk of weight gain and obesity-related conditions like heart disease and diabetes," says Marie-Pierre St-Onge, a professor of nutritional medicine in Columbia's Department of Medicine and Institute for Human Nutrition and study leader. "People tend to gain weight over the course of their adulthood, and obesity is a major risk factor for heart disease. But focusing on eating a healthier diet and getting more physical activity to offset weight gain is simplistic and can be difficult to maintain." 

Studying the effects of chronic, mild sleep deficits

Much of what's known about the link between insufficient sleep and obesity is based on small, brief studies of people who endured severe sleep restriction (usually 4 hours of sleep opportunity). Such studies show that severe sleep deprivation leads to changes in appetite and overeating, which can contribute to weight gain over time.

But most people cannot tolerate severe sleep deprivation for more than a few days.

"These studies only show us what happens under the most extreme conditions and don't tell us if mildly sleep-deprived people, like a lot of Americans who get 5 or 6 hours of sleep a night, will gain weight," St-Onge says. 

Six weeks of short sleep = 1 extra pound

To investigate the effects of chronic mild sleep deprivation, a sleep pattern adopted by roughly 30% of adults, St-Onge and her team recruited 95 adults who usually get 7-8 hours of sleep. Participants were instructed to delay their normal bedtime by 90 minutes for one six-week phase and to get the usual amount of sleep for another six-week phase. Sleep and activity levels were measured throughout each phase with a wrist monitor, along with changes in body weight, waist circumference, body composition, and fasting levels of several hormones known to increase or suppress appetite.

"While the one-pound weight gain observed with modest sleep curtailment is not overwhelming, it is important to remember this is occurring over just six weeks," says Faris Zuraikat, assistant professor of nutritional medicine in Columbia's Department of Medicine and Institute for Human Nutrition and first author of the study. "Our study was designed to mimic sleep patterns that most adults experience chronically. When extrapolated to a full year, we would expect that losing less than an hour and a half of sleep per night could result in clinically meaningful weight gain."

Sedentary time also increased by an average of 17 minutes per day during the sleep-restriction phase overall, and by nearly 30 minutes per day for men and postmenopausal women. 

"Even when we accounted for the fact that they were awake longer when sleep was shortened, participants spent more time being inactive than when they got adequate sleep," Zuraikat says. "This is notable, as people who are more sedentary have elevated risk for chronic diseases."

Why does mild sleep deprivation cause weight gain?

In a previous, related study of a sub-set of the same participants, St-Onge's team reported that women with increased cardiometabolic risk who shortened their sleep by around 80 minutes a night over six weeks had increased insulin resistance, a risk factor for type 2 diabetes. The effects were more pronounced in postmenopausal women.

In another study of this group, St-Onge found that men and women with elevated heart risk had an influx of inflammatory cells in the heart after mild sleep restriction.

"Though more research is needed to further understand how sleep restriction leads to weight gain, all of our findings suggest that insufficient sleep increases the risk of obesity-related conditions like type 2 diabetes and heart disease," St-Onge says. "Now we need to understand the health effects of improving sleep in those who fail to get adequate sleep on a regular basis."