Three quarters of the 196 people in this study were still falling asleep after midnight when the eight weeks ended. They had started out dropping off at around 12:30 a.m., and most never got much earlier. Yet the researchers found something small and oddly specific in the data: the participants who did manage to fall asleep earlier were also the ones who lost more weight.
The trial, from a team at New York University and the University of Delaware, was published on 22 October in the journal Nursing Research. NYU issued a press release on 2 November, and the story has been traveling since. It is worth reading carefully, because the headline version (“go to bed earlier, lose weight”) is tidier than what the data actually show.
Who took part and what they did
The participants were adults aged 21 to 64 who had prediabetes and slept too little. The press release describes them as sleeping under 6.5 hours a night, while one news report quotes a cut-off of six hours, so treat the exact threshold as approximate. All of them joined an eight-week lifestyle program delivered over weekly video calls, covering healthy eating, physical activity and stress management.
One arm of the trial also got a sleep add-on. Those sessions dealt with sleep hygiene, with teaching the brain to treat the bed as a cue for sleep rather than for scrolling, and with a plan to shift bedtime earlier in small steps. Everyone kept a daily sleep diary. Researchers tracked glucose with continuous glucose monitors and measured sleep with wrist-worn actigraphs, before and after the program.
What the team expected, and what happened instead
Lead author Susan Kohl Malone, an assistant professor at NYU’s Rory Meyers College of Nursing, said the team had expected that lengthening sleep would improve glucose and weight loss in short sleepers. That did not happen. Neither program changed glucose levels. According to press coverage, neither group lengthened its sleep by a significant amount; the average gain was only about ten minutes.
What did show up was a link with timing. Across all participants, regardless of which group they were in, each hour earlier that someone fell asleep was associated with about 1.3 pounds (roughly 0.6 kg) of weight loss over the eight weeks. That association held independently of how long people slept. In the sleep group, bedtimes did shift significantly earlier (about 12 minutes on average, according to Malone), and those participants also reported better sleep quality and less daytime sleepiness.
Think about the size of that number. Apply that figure to the average shift of about twelve minutes and the associated difference is a fraction of a pound. Even a full hour earlier, which most participants did not reach, is linked to a bit over a pound across two months. It is a signal, not a weight-loss plan.
Why timing might matter
Malone herself was careful here. She said the study was not designed to test mechanisms, and that the explanation she offers is a working idea rather than something the trial demonstrated. The general reasoning in the field runs along familiar lines: people who stay up late tend to eat later, snack more at night, and may be more out of step with their body clock, which can affect appetite and how the body handles food. If that is what happened here, the bedtime may be a marker of eating patterns rather than a cause of weight change. Our piece on shift work and the body clock covers why mistimed days can ripple into metabolism, though that is background reading rather than an explanation of this particular trial.
An outside expert quoted by Newsweek, Marie-Pierre St-Onge of Columbia University, who was not involved, pointed out that sleep duration was not included in the statistical models, and that the results do not prove extra sleep is unimportant. That is a fair reading. Plenty of earlier research has tied short sleep to weight gain and poorer blood sugar control. One eight-week trial in which sleep barely lengthened cannot overturn that.
What the research does not show
It does not show that going to bed earlier causes weight loss. The timing result is an observed association inside a trial that randomized people to a sleep program, not to a bedtime. People who fell asleep earlier may differ from late sleepers in ways nobody measured: work schedules, meal times, stress, family demands.
It does not show an effect on blood sugar. Glucose did not change in either group, which matters because the participants all had prediabetes, and glucose is the thing the trial’s population most needs to move.
It does not tell us about people without prediabetes, about children or older adults, or about what happens after eight weeks. The press materials gave no confidence intervals or p-values, and I could not access the full paper, so the precision of the 1.3-pound figure is unknown. Malone has said a follow-up study is planned to look for an ideal bedtime threshold and to test whether an earlier bedtime directly produces more weight loss.
A reasonable way to use this
Nothing here is a reason to panic about a midnight bedtime, and nothing in it replaces advice from a doctor if you have been told you have prediabetes. But the finding fits a pattern many people already notice: a late night is often a snack-heavy night. If you want to experiment, the gentlest version is the one the participants were taught, which is to move your bedtime earlier in small steps rather than in one dramatic jump. Fifteen minutes this week, another fifteen next week. Keep the bed for sleep. Dim the room and put the phone somewhere it will not call you back.
Pair that with whatever else is already working for you. Regular meals, a walk after dinner, and fewer late-evening snacks all sit comfortably alongside an earlier bedtime. If your evenings are restless because your mind will not settle, our guide on training your mind to stay calm offers a few practical habits worth trying before bed. And if you are curious about how your body switches between fuels across the day, metabolic flexibility is a useful place to start.
Track it lightly. A note on your phone with the time you fell asleep and how you felt the next day is enough. After a few weeks you will know whether an earlier night makes your days easier, which is a more useful result than any single study can give you.
This article is for general information and is not medical advice. If you have prediabetes, diabetes or a sleep disorder, speak with a qualified health professional before changing your routine.