As important as getting close to eight hours of sleep a night is, new research suggests that going to bed and waking up at the same time every day is just as critical for your health.
The study of more than 1,900 older adults found that those who didn't keep to a regular bedtime and wake time weighed more, had higher blood sugar, higher blood pressure and a higher risk of heart attack or stroke within 10 years.
Perhaps obesity disrupts sleep, said lead study author Jessica Lunsford-Avery, an assistant professor of psychiatry and behavioral sciences at Duke University in Durham, N.C.
"Or, as some research suggests, perhaps poor sleep interferes with the body's metabolism, which can lead to weight gain, and it's a vicious cycle," she added in a university news release.
"With more research, we hope to understand what's going on biologically, and perhaps then we could say what's coming first or which is the chicken and which is the egg," Lunsford-Avery said.
Irregular sleepers were also more likely to say they suffered from depression and stress than those who stuck to regular sleep patterns.
In terms of race, blacks made up the largest proportion of irregular sleepers, compared with whites, Asian-Americans or Hispanics, the researchers found.
The findings show an association between irregular sleep and health, but cannot prove that one causes the other, the researchers cautioned.
"From our study, we can't conclude that sleep irregularity results in health risks, or whether health conditions affect sleep," Lunsford-Avery said. "Perhaps all of these things are impacting each other."
For the study, participants aged 54 to 93 used devices that tracked sleep schedules down to the minute. This enabled the researchers to pinpoint exact bedtimes.
The investigators also kept track of when participants went to bed and how long they slept. They found that people with high blood pressure tended to sleep longer, and obese people tended to stay up later.
Of all the things the team measured, however, keeping regular hours turned out to be the best predictor of heart and metabolic health. Irregular sleepers experienced more sleepiness during the day and were less active -- perhaps because they were tired, Lunsford-Avery said.