In a trial of adults with prediabetes, the people who lost the most weight weren’t the ones who slept longer, but the ones who went to bed earlier
Short sleep has long been linked to weight gain and diabetes, so researchers at NYU Rory Meyers College of Nursing tested a simple idea: help people sleep more, and they might lose more weight. They recruited 196 adults aged 21 to 64 with prediabetes who usually slept less than six and a half hours a night. Everyone took part in an eight-week diabetes prevention program covering diet, exercise and stress. Half also got sleep coaching, including a plan to move their bedtime gradually earlier.
Sleep coaching worked on sleep. People in the coaching group reported better sleep quality and less daytime sleepiness, and their sleep timing shifted significantly earlier. But adding sleep coaching did not change blood sugar, and it did not lead to more weight loss than the standard program on its own.
The surprise came when the researchers looked at everyone together. Regardless of which group people were in, those who fell asleep earlier lost more weight, and that link held independent of how long they slept.
“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 lead author Susan Kohl Malone, an assistant professor at NYU.
“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,” she added. “However, our findings do raise the possibility that earlier sleep onset, independent of sleep duration, could be a promising target for improving metabolic health.”
Earlier research has pointed in a similar direction. In a 2018 trial in the American Journal of Clinical Nutrition, habitual short sleepers who were coached to extend their sleep cut their intake of free sugars by about 10 grams a day over four weeks compared with a control group.
Why might bedtime matter? Going to bed later can mean more evening hours for snacking, but the researchers say timing may matter in other ways too, including how well sleep lines up with the body’s internal clock, which governs appetite hormones and how the body handles energy.
The second finding is a caution about expectations. Eight weeks of better sleep did not move blood sugar, which may take longer to change. Sleep habits also affect the people around us, as a study of couples’ sleep and eating found, and late body clocks have long-term costs, as research on night owls suggests.
For people trying to lose weight, the practical takeaway is modest but easy to try: an earlier, consistent bedtime costs nothing and may help, alongside the diet and exercise changes that drive most weight loss.
There are limits to what this shows. The link between earlier sleep and weight loss came from looking across all participants, not from the randomized comparison, so it cannot prove that going to bed earlier causes weight loss. The program lasted only eight weeks, and sleep quality was partly self-reported. The study was funded by the US National Institute of Nursing Research.
Source
Malone SK, et al. “Randomized Controlled Trial of Lifestyle Plus Sleep Extension Intervention on Adults With Prediabetes and Short Sleep.” Nursing Research, 2026.
DOI: 10.1097/NNR.0000000000000957
Also cited
Al Khatib HK, Hall WL, Creedon A, et al. “Sleep extension is a feasible lifestyle intervention in free-living adults who are habitually short sleepers: a potential strategy for decreasing intake of free sugars? A randomized controlled pilot study.” American Journal of Clinical Nutrition, 2018.
DOI: 10.1093/ajcn/nqx030
