Does Your Bedtime Affect Your Metabolism?

Staying up an extra hour doesn’t just impact tomorrow’s energy levels – it could impact your weight, and potentially increase the odds of developing diabetes. Yikes!

A study published in the journal Sleep found that changing bedtimes among people who weren’t shift workers had an impact on their metabolic health. Researchers looked at 338 women ages 48 to 58 who tracked their sleep habits daily for about 14 days. Five years later, those women tracked their sleep habits for another 14 days, and scientists looked at their weight, body mass index (BMI) and insulin resistance.

Greater variability in bedtime, and greater bedtime delays, were associated with higher insulin resistance. That means excess glucose builds up in their bloodstream, leading to diabetes and prediabetes, according to the National Institute of Diabetes and Digestive and Kidney Diseases. Simply put, changing the time you crawl into bed throughout the week, and pushing your bedtime later may lead to insulin resistance that can increase the likelihood of developing diabetes.

Insulin helps your body absorb glucose from food and use it for energy, some of which will be stored away and put into use while your body sleeps. When bedtime is delayed, your body continues to collect sugar from food (even if you’re not eating), until sometimes those stores become so full that blood sugars get converted into fat cells, says Briana Milligan, a doctoral candidate at the University of Pittsburg. When sleep is delayed, the body keeps storing sugar rather than using it for energy. Theoretically, this is why poor sleep could be linked to poor metabolic health, says Milligan.

The study data suggest that women who stuck to a bedtime within an hour of their typical bedtime tended to have less insulin resistance than women who deviated beyond one hour.

“Looking closely at the data, we also found that weekday-weekend differences in bedtime were especially important,” says Milligan. In other words, women who had a regular bedtime every night, no matter the day of the week, kept their insulin under better control.

Diabetes risk increases in midlife women, and this study suggests that irregular sleep schedules leading to insulin resistance may be an important piece of this puzzle, says Milligan.

Additionally, more time spent in bed before bedtime was associated with higher BMI, which is an indicator used to determine if someone is overweight or obese. The researchers wonder if folks spending more time in bed were more sedentary.

“Although we cannot be certain that our findings will generalize to men and women of all ages, other research has found similar results in other age groups,” Milligan says. For example, studies published in the journal Sleep have found that late and irregular sleep timing is associated with higher BMI and obesity risk in teenagers.

Insulin isn’t the only reason people who don’t have optimum sleep habits may struggle more with their weight. Research from the University of Chicago published in the journal Sleep looked at normal healthy sleepers, and examined how sleep loss affected their appetite and food choices. The participants who didn’t get enough sleep and ate a huge meal still caved to the temptations of sweet and salty snacks soon afterward in a way that their well-slept counterparts didn’t. Keep this in mind the next time you eat out!

“We also found their hormones, like leptin and ghrelin, can be affected when sleep-deprived,” says Conroy. Ghrelin is the hunger hormone, and leptin is the satiety hormone. So, sleep less, and these hormones don’t function properly, which can make you want to eat more. Yikes!

Quality and Quantity

There’s also some concern that going to bed later may also be associated with increased calories consumed at night, Milligan says. Research shows the body’s ability to metabolize glucose is higher early in the day, she says. The next step is for researchers to study “night owls” and “morning birds,” and any differences in metabolism, says Milligan.

Ultimately, the lesson is this: If you’re looking to shed pounds for beach season, or just get healthier overall, make sure you’re focusing on your sleep schedule as much as you are your diet and exercise routine.

Curious about what else sleep impacts? Check out this blog post that explains why you might get sick when you’re overtired.