New research suggests that falling asleep earlier may be tied to greater weight loss in adults with prediabetes, though the study’s authors caution the finding does not prove that an earlier bedtime causes people to shed pounds.
The analysis, drawn from a randomized trial led by NYU’s Rory Meyers College of Nursing, found that each hour earlier a participant fell asleep corresponded with about 1.3 pounds of weight loss over an eight-week period. The research was published in the journal Nursing Research.
“When we fall asleep — not just how much we sleep — seems to be an important and overlooked factor for weight loss and metabolic health,” said Susan Kohl Malone, an assistant professor at the nursing college and the study’s lead author.
How the study worked
Researchers followed 196 adults with prediabetes who reported sleeping fewer than 6.5 hours a night on a regular basis. Half of the participants completed an eight-week program covering diet, exercise and stress management. The other half received the same program plus behavioral coaching designed to gradually move their bedtime earlier.
Participants’ blood sugar, sleep and physical activity were monitored through sensors, sleep diaries and wrist-worn devices throughout the trial.
Mixed results
Neither group saw meaningful improvement in blood sugar levels. Both groups lost weight overall, but those who received sleep coaching did not lose significantly more weight than those who received lifestyle education alone.
“While we expected that extending sleep would improve glucose levels and weight loss in adults with prediabetes who sleep for shorter periods, this wasn’t the case in our study,” Malone said.
Still, participants in the coaching group reported sleeping better, feeling less drowsy during the day, and gradually moving their bedtimes earlier. On average, that group fell asleep about 12 minutes earlier than before — a shift that produced no measurable change in blood sugar.
When researchers looked across both groups together, they found that participants who shifted toward earlier sleep times tended to lose more weight, regardless of which program they were in.
A possible explanation
The researchers pointed to the body’s internal clock as a possible factor. Staying up late increases exposure to artificial light, which may trigger the body’s stress response and disrupt hormones that control hunger. Late hours also line up with the period when human insulin sensitivity is at its lowest point.
“In contrast, falling asleep earlier may limit late-night eating and better align food intake with the body’s optimal metabolic window,” Malone said.
What the study doesn’t show
The trial lasted only eight weeks, so it remains unclear whether participants could keep an earlier bedtime or sustain any weight loss over the long run. Researchers also relied heavily on self-reported logs for key measures such as sleep quality and daytime drowsiness, even though participants wore wrist monitors. The results reflect an association found across the study group, not proof that earlier sleep directly causes weight loss.
The study was funded by the National Institute of Nursing Research, part of the National Institutes of Health, and was carried out with researchers from the University of Delaware.
