Adults with prediabetes who fell asleep earlier tended to lose more weight, a new study suggests. The results show a link, though they don’t establish that shifting bedtime earlier directly causes weight loss.
Researchers at the NYU Rory Meyers College of Nursing analyzed data from a randomized trial. Across an eight-week period, each hour earlier that participants fell asleep was associated with about 1.3 pounds of weight loss.
“When we fall asleep—not just how much we sleep—may be an important, often overlooked factor in weight loss and metabolic health,” said lead researcher Susan Kohl Malone, an assistant professor at the college.
The study, published in Nursing Research, included 196 adults with prediabetes who typically slept fewer than 6.5 hours a night. One group took an eight-week course covering diet, exercise and stress management. The other received the same education, along with coaching to move bedtime earlier in gradual steps.
Researchers monitored participants’ blood sugar, sleep and activity using sensors, sleep logs and wrist-worn devices. Neither group had a significant improvement in blood sugar. Both groups lost weight, but those who received sleep coaching did not lose significantly more than the group that received lifestyle education alone.
“We expected that extending sleep would improve glucose levels and weight loss in adults with prediabetes who sleep for shorter periods, but that wasn’t what we found,” Malone said.
People in the sleep-coaching group reported better sleep quality and less daytime drowsiness, and gradually began going to bed earlier. In a separate analysis of participants across both groups, those who shifted their sleep earlier tended to lose more weight.
The researchers said the body’s internal clock could help explain the association. Staying up late can mean more exposure to artificial light, which may trigger the body’s stress response and affect hormones involved in hunger. Late nights also overlap with the time of day when insulin sensitivity is lowest.
“Falling asleep earlier may reduce late-night eating and help align food intake with the body’s optimal metabolic window,” Malone said.
The trial lasted just eight weeks, so it’s not clear whether participants would maintain earlier bedtimes or keep the weight off over time. Although they wore wrist monitors, some measures—including sleep quality and daytime drowsiness—relied largely on participants’ own reports. The findings also show an association, not cause and effect.
Participants who received sleep coaching fell asleep about 12 minutes earlier on average, Malone said. That change did not produce a measurable improvement in blood sugar levels.
The research was funded by the National Institute of Nursing Research, part of the National Institutes of Health, and conducted with researchers from the University of Delaware.
