How mild sleep loss can lead to weight gain, a Columbia University study finds

Sleep is usually the first thing we cut back on. You fire off one last email, watch one more episode, take one more scroll, and before you know it, it is after midnight.

It is easy to assume that losing the odd hour does not really matter. A research team at Columbia University Vagelos College of Physicians and Surgeons set out to test whether that assumption holds up.

A small change in bedtime

The researchers enrolled 95 healthy adults who typically slept seven to eight hours each night. Everyone took part in two distinct six-week phases.

During one phase, participants kept to their normal sleep routine. During the other, they delayed their usual bedtime by 90 minutes.

That difference was deliberately modest, reflecting the sort of everyday shortfall that can accumulate without any conscious decision to stay up late.

What the trackers measured

Throughout both phases, a wrist-worn device continuously recorded sleep and physical movement. This meant the study did not depend on people estimating how long they had slept.

Alongside the tracker data, the team measured body weight, waist circumference, body composition, and fasting levels of several hormones linked to hunger and satiety.

Taken together, these measures provided a far more complete picture than a set of scales alone.

Why mild sleep loss matters

Around 30% of adults already live with this kind of reduced sleep, often unintentionally. Even so, much of the evidence connecting sleep and weight comes from more severe experiments where participants slept for only about four hours per night.

“These studies only show us what happens under the most extreme conditions and don’t tell us if mildly sleep-deprived people, like a lot of Americans who get 5 or 6 hours of sleep a night, will gain weight,” said Marie-Pierre St-Onge, a study leader.

We already know that drastic sleep restriction can disrupt appetite and steer people towards overeating.

The problem is that very few people can sustain such an extreme schedule for more than a short period, which limits what those studies can reveal about more typical sleep loss.

Six weeks, one extra pound

After the reduced-sleep phase ended, participants were heavier. On average, they put on about 0.45 kg (one pound).

“While the one-pound weight gain observed with modest sleep curtailment is not overwhelming, it is important to remember this is occurring over just six weeks,” said Faris Zuraikat, first author of the study.

“Our study was designed to mimic sleep patterns that most adults experience chronically.”

“When extrapolated to a full year, we would expect that losing less than an hour and a half of sleep per night could result in clinically meaningful weight gain.”

Moving less while awake

The increase on the scales was only part of what changed. With less sleep, participants also tended to be less active during the day.

Across the full group, sedentary time increased by about 17 minutes per day. In men and postmenopausal women, the rise was close to 30 minutes.

Many people find this counterintuitive because less sleep creates more waking time. In practice, those additional hours did not translate into additional movement.

“Even when we accounted for the fact that they were awake longer when sleep was shortened, participants spent more time being inactive than when they got adequate sleep,” Zuraikat said.

“This is notable, as people who are more sedentary have elevated risk for chronic diseases.”

Past research on impact of sleep loss

Previous research involving the same participant group suggested other changes that are less visible than weight gain. The extra weight is easy to spot, but it is not the only shift that may matter.

In one study, women with higher cardiometabolic risk who reduced their sleep by roughly 80 minutes developed greater insulin resistance.

This is an early signal associated with type 2 diabetes, indicating the body has to work harder to regulate blood sugar.

The impact was strongest in postmenopausal women, suggesting that age and hormonal changes may alter the cost of a sleep shortfall.

Another study focused directly on the cardiovascular system. Among men and women at increased risk of heart problems, mild sleep restriction was followed by an influx of inflammatory cells-low-grade inflammation that commonly accompanies heart disease.

What better sleep could bring

“Our study shows that getting adequate sleep may help reduce the risk of weight gain and obesity-related conditions like heart disease and diabetes,” St-Onge said.

“People tend to gain weight over the course of their adulthood, and obesity is a major risk factor for heart disease.”

But focusing on eating a healthier diet and getting more physical activity to offset weight gain is simplistic and can be difficult to maintain.”

Implications of the study

The message is not that diet and exercise are unimportant. Rather, sleep should be treated as part of the same discussion, because it may quietly influence health in the background.

“Though more research is needed to further understand how sleep restriction leads to weight gain, all of our findings suggest that insufficient sleep increases the risk of obesity-related conditions like type 2 diabetes and heart disease,” St-Onge said.

“Now we need to understand the health effects of improving sleep in those who fail to get adequate sleep on a regular basis.”