Falling asleep earlier was associated with greater weight loss among adults with prediabetes, according to an analysis of data from a randomized trial led by the NYU Rory Meyers College of Nursing. The result points to sleep timing as an important factor, while stopping short of proving that an earlier bedtime causes weight loss.

Across the eight week study, each hour earlier that participants fell asleep was associated with roughly 1.3 pounds of weight loss. Researchers described that figure as a statistical projection based on results across the study group.

The investigation, published in the journal Nursing Research, evaluated 196 adults diagnosed with prediabetes. All participants routinely recorded fewer than 6.5 hours of sleep each night.

Half of the participants joined an eight week lifestyle education course covering diet, exercise and stress. The other half received the same training along with behavioral coaching designed to help them gradually move their bedtimes earlier.

Researchers monitored blood sugar, sleep and physical activity throughout the trial. They collected information through sensors, sleep logs and monitors worn on participants’ wrists.

Neither group experienced significant improvements in blood sugar. Both groups lost weight, but the people who received sleep coaching did not lose significantly more than those who received lifestyle education alone.

The sleep coaching group did report better sleep quality and less daytime drowsiness. Those participants also gradually began going to bed earlier during the study period.

“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,” Susan Kohl Malone, an assistant professor at the nursing college and the study’s lead author, said.

Although the coaching program did not produce a significant weight loss advantage over lifestyle education, researchers conducted a separate analysis combining participants from both groups. In that analysis, people who shifted their sleep earlier tended to lose more weight.

The statistical projection found that every 60 minutes earlier a participant fell asleep was associated with roughly 1.3 pounds of weight loss over eight weeks. The researchers emphasized that the finding represented an association rather than proven cause and effect.

The body’s internal clock could help explain the observed relationship, researchers suggested. Staying awake late can increase exposure to artificial light, which may activate the body’s stress response and affect hormones involved in regulating hunger.

Late waking hours also overlap with a period when human insulin sensitivity is at its lowest. Researchers noted that remaining awake late can elevate hunger hormones such as ghrelin and increase the likelihood of late night eating.

“In contrast, falling asleep earlier may limit late-night eating and better align food intake with the body's optimal metabolic window,” Malone said.

The trial’s short duration leaves important questions unanswered. Because it lasted only eight weeks, researchers could not determine whether participants would maintain earlier bedtimes or sustain their weight loss over a longer period.

Although participants wore wrist monitors, important measures such as sleep quality and daytime drowsiness depended heavily on information they reported themselves. That reliance on sleep logs was another limitation of the research.

Participants who received sleep coaching fell asleep about 12 minutes earlier on average, according to Malone. That relatively modest change produced no measurable improvement in blood sugar levels.

The findings therefore separate sleep timing from total sleep duration without establishing that changing bedtime directly produces weight loss. They also show that the coaching intervention itself did not significantly outperform lifestyle education for weight loss or blood sugar improvement.

The study received funding from the National Institute of Nursing Research, which is a division of the National Institutes of Health. Researchers from the University of Delaware collaborated on the investigation.