A study has found that cutting sleep by a little over an hour a day can lead to weight gain.

Medical News Today (MNT) reported on July 7 local time that adults who typically slept 7 to 8 hours gained about 0.5 kg over six weeks when they delayed bedtime by about 90 minutes and slept 78.4 minutes less on average.

Researchers conducted two six-week experiments involving 95 adults who usually slept 7 to 8 hours a day. In one period, participants maintained their usual sleep habits. In the other, they went to bed about 90 minutes later than usual. The actual average reduction in sleep was 78.4 minutes. The researchers tracked sleep and physical activity with wrist monitors and measured weight, waist circumference, body composition and changes in fasting appetite-regulating hormones.

The key is persistence, not the intensity of sleep deprivation. The study reflected mild sleep loss at a level many adults experience, rather than extreme conditions such as sleeping 4 hours a night. Marie-Pierre St-Onge (마리 피에르 생통주), founding director of Columbia University's Sleep and Circadian Research Center, said sustained reduced sleep can lead to increases in weight and waist circumference.

The study also confirmed a decline in activity levels. During the sleep-restriction period, participants' sedentary time increased by an average of 17 minutes a day. The increase was close to 30 minutes a day among men and postmenopausal women. Researchers said the pattern suggested that participants spent the additional time in a more inactive way, rather than simply being awake longer.

St-Onge said earlier research found that participants tended to eat more when sleep was restricted, and that sleep loss could spur both increased food intake and reduced activity.

The findings also align with earlier research analyzing the same participant group. Women with high cardiometabolic risk showed increased insulin resistance after mild sleep restriction, with effects particularly pronounced in postmenopausal women. St-Onge said earlier work confirmed that glucose tolerance and insulin sensitivity decline with sleep loss and said this could lead over time to prediabetes and type 2 diabetes.

Another related study observed signals of increased inflammatory cells in the heart among participants with high cardiovascular risk after long-term mild sleep restriction. The research supports the possibility that sleep affects not only weight changes but overall metabolic and cardiovascular health.

The researchers said they could not conclude that sleep loss directly causes weight gain in everyone. Factors such as diet, genetics, stress and physical activity also affect weight and health. Still, they stressed that sufficient sleep should be considered a key element of health management, alongside diet and exercise.

St-Onge said increasing time in bed is necessary to extend sleep, but lying in bed without falling asleep does not help. She advised calculating bedtime by working backward from wake-up time based on an individual's circumstances, and reducing evening activities or shifting them to other times. She added that timing of caffeine intake, eating right before bedtime and activities that raise stress also need adjustment.

Researchers said that even a change that appears small, such as sleeping about 80 minutes less each day, could lead to meaningful weight gain over the long term. They plan further work to examine whether actually increasing sleep among people who typically do not get enough can reduce the risks of obesity, type 2 diabetes and heart disease.