People who don’t consistently get the same amount of sleep or go to bed at the same time each night may be more likely to develop health problems like obesity, high blood pressure, high cholesterol and diabetes, a recent study suggests.
Lack of sleep has long been linked to a wide range of so-called metabolic abnormalities, including obesity, high blood pressure, high cholesterol, and diabetes. But much of this research focused on the effect of the average amount of sleep people get, and not on how much sleep routines varied from one day to the next, said study coauthor Tianyi Huang, of Brigham and Women’s Hospital and Harvard Medical School in Boston.
“In this study, we showed that high night-to-night differences in sleep schedules (either duration or timing) are associated with higher risk of developing metabolic problems, particularly multiple metabolic abnormalities at the same time,” Huang said by email.
“Importantly, this finding is independent of sleep duration/quality, that is, more irregular sleep schedules are associated with higher metabolic disease risk no matter one has short or long sleep duration or has good or poor sleep quality,” Huang added. “The negative impact of short sleep duration on some nights cannot be compensated for by extended longer sleep duration on other nights,” Huang said by email.
As reported in Diabetes Care, the researchers had 2,003 patients do home-based sleep studies for one week using devices known as actigraphs, which assess nighttime movements and sleep-wake cycles.
On average, these people got about 7.15 hours of sleep each night and went to bed at around 11:40 p.m. Roughly two-thirds of them had more than one hour of variation in sleep duration, and 45% of them had more than one hour of variation in their bedtime.
A total of 707 participants, or 35%, had so-called metabolic syndrome, or multiple types of metabolic abnormalities that increase the risk for heart disease, including increased blood pressure, high blood sugar, excess body fat around the waist, and abnormal cholesterol or triglyceride levels.
Compared to people who had less than one hour of variation in sleep duration, people whose sleep duration varied by 60 to 90 minutes were 27% more likely to have metabolic syndrome. The increased risk rose to 41% for people with 90 to 120 minutes of variation in sleep duration, and jumped to 57% with more than two hours of variation in sleep duration.
Compared with people with no more than a half hour of variation in their nightly bedtime, people whose bedtime varied by 30 to 60 minutes had a similar risk for metabolic syndrome. But the risk was 14% higher when bedtimes varied by 60 to 90 minutes and 58% higher when bedtimes varied by more than 90 minutes.
The study wasn’t a controlled experiment designed to prove whether or how shifts in sleep duration or bedtimes might directly cause metabolic syndrome.
“The reason increased variability has a detrimental effect on metabolic heath may have to do with our biological clocks,” said Kristen Knutson, a researcher at Northwestern University Feinberg School of Medicine in Chicago who wasn’t involved in the study.
“We have internal 24-hour rhythms of many processes that impact metabolism and for optimal function these rhythms should be synchronized with each other and with the environment,” Knutson said by email. “If we are sleeping at different times and different amounts, our internal clocks may have difficulty staying synchronized, which may impair function.”
One limitation of the analysis is that researchers only assessed sleep during that one week, and it’s possible the week-long sleep study didn’t reflect sleep patterns over longer periods of time. Researchers also lacked data on several factors that can impact sleep regularity like breakfast consumption and meal timing, both of which can also impact metabolic health.
Most adults need at least 7 hours of sleep a night, according to the U.S. Centers for Disease Control and Prevention.
To get the ideal amount of sleep and avoid nighttime awakening and sleep disturbances that make people wake up feeling unrested, the CDC recommends setting a consistent bedtime, sleeping in a dark room without any electronics around, and avoiding large meals, caffeine, and alcohol before bedtime.