Most sleep advice for weight and blood sugar focuses on one number: how many hours you get. A new randomized trial from New York University points to another factor that gets far less attention, which is when you fall asleep. Researchers worked with adults who had prediabetes and were chronically short on sleep. People who started falling asleep earlier tended to lose more weight over eight weeks, and that link held regardless of how long they slept.
The result is interesting but easy to overstate, so below we cover what the study tested, what it found, what it didn't find, and what you can reasonably do with it.
What the researchers tested
The study, led by Susan Kohl Malone, an assistant professor at NYU Rory Meyers College of Nursing, was published in the journal Nursing Research. The team enrolled 196 adults aged 21 to 64 who had prediabetes and were sleeping under 6.5 hours a night, well short of the seven or more hours generally recommended for adults.
Participants were randomly assigned to one of two eight-week programs, both delivered over weekly video calls:
- Lifestyle only: a diabetes-prevention style program covering diet, physical activity, and stress management.
- Lifestyle plus sleep: the same program, plus a sleep component. That meant sleep hygiene coaching, techniques to help the brain link bed with sleep rather than wakefulness, and a step-by-step plan to move bedtime earlier and add sleep gradually.
Everyone kept a daily sleep diary. Before and after the program, participants also wore a continuous glucose monitor and a research-grade wrist activity tracker (an actigraph), which gave the researchers objective measurements to check against the diaries.
What they found
The findings fall into three parts, and it helps to keep them separate.
1. Blood sugar didn't budge
The team had expected that helping people sleep longer would improve their glucose. It didn't, in either group. "This wasn't the case in our study," Malone acknowledged. For a trial built around diabetes prevention, that's an important result in itself.
2. The sleep program improved sleep
Both groups slept better and lost weight. The group that got sleep coaching did better on sleep: they reported larger improvements in sleep quality and daytime sleepiness, and their sleep schedule moved significantly earlier.
3. Earlier sleep onset tracked with weight loss
When the researchers looked at all participants together, regardless of group, each hour earlier that someone fell asleep was associated with roughly 1.3 pounds (0.6 kg) of additional weight loss over the eight weeks. That association held independent of total sleep duration. In other words, it wasn't just that early sleepers slept longer. "When we fall asleep—not just how much we sleep—seems to be an important and overlooked factor," Malone said.
Want to move your bedtime earlier without fighting it?
Our free Sleep Schedule Builder creates a personalized schedule from your wake time and current habits, so you can shift your bedtime in small, realistic steps.
How to read this result
It's worth being precise about what kind of evidence this is. The trial was randomized, but the randomized comparison (lifestyle only versus lifestyle plus sleep) showed differences in sleep quality and sleepiness, not in glucose. The weight-timing finding comes from looking across everyone in the study. That makes it an association. People who shifted earlier may have differed in other ways, such as motivation or how closely they followed the diet and exercise advice.
The scale also matters. About 1.3 pounds per hour earlier, over two months, is modest. It's a nudge on top of diet and activity, not a substitute for them. The study was also fairly small and short, and everyone in it had prediabetes and short sleep, so the results may not apply to people who already sleep seven to nine hours.
Still, the finding is consistent with a growing body of research suggesting that sleep timing and regularity, not just duration, are tied to metabolic health. We've covered related findings on weekend catch-up sleep and blood pressure and on personal short-sleep thresholds.
Why earlier sleep might matter
The researchers proposed several possible explanations. None were directly tested in this trial, so treat them as reasonable hypotheses rather than established mechanisms:
- Less late-night eating. Malone suggested that "falling asleep earlier may limit late-night eating." That may also move food intake to a time of day when the body handles insulin better.
- Less artificial light at night. Bright evening light, especially from screens, can delay the body clock. Our explainer on how blue light affects your sleep covers this.
- A calmer nervous system. Late nights may keep the sympathetic "fight or flight" system more active.
- Less hunger signaling. Short and late sleep are linked to higher levels of ghrelin, the hormone that drives appetite. We explain the ghrelin and cortisol connection in Sleep and Weight Loss: What the Science Actually Shows.
Practical steps if you want to try it
- Shift gradually. The trial's sleep program moved bedtime earlier in increments, not all at once. Moving 15 to 20 minutes earlier every few nights is much easier than jumping an hour.
- Anchor your wake time. A consistent wake-up time, including weekends, is what makes an earlier bedtime stick. Without it, you'll just lie awake.
- Close the kitchen earlier. If late-night snacking is part of your evening, an earlier bedtime and an earlier "last call" for food reinforce each other.
- Dim the evening. Lower the lights and put screens away in the last hour so your body clock gets the signal that night has started. Our sleep hygiene tips cover the basics.
- Don't force it. If you go to bed early but lie awake for a long time, get up and do something calm until you feel sleepy. Strengthening the link between bed and sleep was part of the trial's program, and it's a core technique of CBT for insomnia.
- Keep the bigger plan. If you have prediabetes, sleep changes should add to the diet, activity, and medical follow-up your doctor recommends, not replace them.
Key takeaways
- An NYU randomized trial of 196 short-sleeping adults with prediabetes compared an eight-week lifestyle program with and without added sleep coaching.
- Neither program changed blood glucose. Both improved sleep and led to weight loss.
- The sleep-coaching group reported better sleep quality and less daytime sleepiness, and shifted their sleep timing earlier.
- Across all participants, each hour earlier of sleep onset was associated with about 1.3 lb (0.6 kg) more weight lost, independent of sleep duration.
- It's an association from a small, short study, but it adds to evidence that when you sleep matters alongside how long you sleep.
An earlier bedtime won't replace diet and exercise, and this study doesn't show that it will lower blood sugar. But if you regularly fall asleep well after midnight, it's a low-risk change to try, and it could make your other health habits easier to keep.
Source: Medical Xpress (provided by New York University) — "Earlier bedtime linked to greater weight loss in prediabetes trial," November 3, 2026, https://medicalxpress.com/news/2026-11-earlier-bedtime-linked-greater-weight.html. Study: Malone SK, Hu J, Goyal C, Patterson F, D'Eramo Melkus G, Nursing Research (2026), doi:10.1097/nnr.0000000000000957.
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. If you have prediabetes or diabetes, talk to your doctor before making significant changes to your diet, activity, sleep schedule, or medications.
About Better Night Sleep: Better Night Sleep is an independent sleep-education and product-research resource. Our articles are written and edited by the Better Night Sleep editorial team using reputable public sources and established sleep-health recommendations. Learn more about us.