How Much Should You Sleep? Too Much, Too Little Both Affect Metabolism

Are you usually late to bed and early to rise? Or do you find yourself getting excessive shut-eye? Findings from a recent Korean study identified the health effects linked to sleeping too much or not sleeping enough. 

The study titled "Association between sleep duration and metabolic syndrome: a cross-sectional study" was published in the journal BMC Public Health on June 13.

The research team from Seoul National University College of Medicine examined 133,608 Korean men and women aged 40 to 69 years. The participants underwent physical examinations by medical professionals in addition to having their blood cells, genomic DNA, plasma samples, serum, urine, etc. collected. 

"This is the largest study examining a dose-response association between sleep duration and metabolic syndrome and its components separately for men and women," said lead author Claire E. Kim. "Because we were able to expand the sample of our previous study, we were able to detect associations between sleep and metabolic syndrome that were unnoticed before."

The question "In the past year, on average, how many hours/minutes of sleep (including daytime naps) did you take per day?" was asked to determine the sleep duration of the participants. 

The findings revealed lesser than six hours of sleep and more than ten hours of sleep per day were associated with the cluster of conditions known as metabolic syndrome. These conditions can include blood pressure, high blood sugar, excess body fat around the waist and unhealthy cholesterol levels.

As per general guidelines by the National Sleep Foundation, most adults can benefit from getting 7 to 9 hours of sleep while those older than 65 can ideally aim for 7 to 8 hours.

The study found 11 percent of men and 13 percent of women slept less than six hours, while 1.5 percent of men and 1.7 percent of women slept more than ten hours. 

"We observed a potential gender difference between sleep duration and metabolic syndrome, with an association between metabolic syndrome and long sleep in women and metabolic syndrome and short sleep in men," Kim added.

Among those who slept fewer than six hours, men were more likely to have metabolic syndrome and higher waist circumference while women were more likely to have higher waist circumference. 

With men who slept for more than ten hours a day, the study found they were more likely to have metabolic syndrome and increased levels of triglycerides. Meanwhile, women who slept for a similarly excessive duration were more likely to have metabolic syndrome with higher waist circumference, increased levels of triglycerides and blood sugar, and low levels of "good" cholesterol.

A number of limitations were noted in the study. Because it was cross-sectional, causality between sleep duration and metabolic syndrome could not be established. Inaccuracies may have also occurred since the average sleep duration was self-reported by the participants.