Researchers at New York University's Rory Meyers College of Nursing have reported an unexpected link between sleep and weight loss — one tied not to how long a person sleeps, but to when they fall asleep. The findings, covered by Sky News Arabia, suggest that bedtime timing may matter more for metabolic health than earlier research had recognised.
The study focused on people diagnosed with prediabetes, a condition in which blood sugar is above normal but not yet high enough to be classified as type 2 diabetes. Such individuals face a heightened risk of developing type 2 diabetes, particularly if they are overweight or obese, have elevated glucose levels, high blood pressure, or are physically inactive.
Suzan Coul Malone, an assistant professor at the nursing school and the study's lead researcher, said sleep timing — not just sleep duration — appears to be an overlooked factor in weight loss and metabolic health, according to Sky News Arabia.
Why it matters
Prediabetes is a widespread precursor to a disease that carries serious long-term health consequences, and the study points to a low-cost behavioural lever — going to bed earlier — that may complement existing lifestyle interventions. The research also shifts attention away from the near-exclusive focus on sleep quantity in public health messaging, suggesting that when a person sleeps deserves closer scrutiny alongside how long they sleep.
How the trial was designed
The team recruited 196 people aged between 21 and 64 and randomly assigned them to two groups. The first, serving as the control group, followed an eight-week programme aimed at improving lifestyle habits. The second completed the same programme but also received coaching and guidance sessions designed to improve their sleep habits.
All participants were at elevated risk of type 2 diabetes and were accustomed to sleeping less than six and a half hours per night.
Notably, the sleep coaching did not produce a marked change in blood sugar readings, even though participants reported feeling more alert and energetic during the day. But when the researchers analysed the data, a striking pattern emerged among those who received the sleep guidance: people who began going to bed earlier showed a noticeable shift in blood glucose levels, regardless of how many hours they slept.
Malone suggested that falling asleep earlier may help curb late-night eating and bring mealtimes into closer alignment with the body's optimal window for metabolic processes, Sky News Arabia reported.
What the numbers showed
The study, published in the journal Nursing Research, found that earlier sleep onset was associated with greater weight loss over the eight weeks, and that this relationship held independently of total sleep duration.
After statistical analysis, the researchers observed that the earlier a person went to bed and fell asleep, the more weight they lost on average. Each hour of earlier sleep onset was linked to roughly 1.3 pounds — about 0.6 kilograms — of additional weight loss across the eight weeks.
The scientists offered several possible explanations. Beyond reducing opportunities for late-night snacking, an earlier bedtime may cut down the time spent in front of electronic screens and limit exposure to artificial light at night. Early sleep may also be tied to biological changes in the activity of the sympathetic nervous system, the branch responsible for the body's stress response. It may additionally affect ghrelin, known as the "hunger hormone," which plays a central role in regulating appetite and feelings of hunger. More broadly, going to bed earlier may reduce the environmental cues that drive stress and disrupt the regulation of appetite and hunger.
Limits and next steps
The researchers stress that the study is not conclusive and carries several limitations. The trial was confined to people at risk of type 2 diabetes and ran for only eight weeks, which restricts how far the results can be generalised to the wider population. The observed relationship between sleep timing and weight loss also does not prove that earlier sleep is the direct cause of the reduction in weight.
Despite these caveats, the findings open a new avenue in research on sleep and health. Rather than concentrating solely on the number of hours slept, the study indicates that the timing of sleep itself — and how well it aligns with the body's biological clock — merits investigation for its effects on metabolism and weight control.
