Researchers at Seoul National University College of Medicine found that compared to individuals who slept six to seven hours per day, men who slept fewer than six hours were more likely to have metabolic syndrome and higher waist circumference.

Women who slept fewer than six hours were more likely to have higher waist circumference. Sleeping more than ten hours per day was associated with metabolic syndrome and increased levels of triglycerides in men, and with metabolic syndrome, higher waist circumference, higher levels of triglycerides and blood sugar, as well as low levels of 'good' cholesterol (HDL-C) in women.

The authors found that nearly 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. Claire E. Kim, lead author of the study said, "This is the largest study examining a dose-response association between sleep duration and metabolic syndrome and its components separately for men and women.

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. 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."

Based on common definitions, participants were considered to have metabolic syndrome if they showed at least three of the following: elevated waist circumference, high triglyceride levels, low levels of 'good' cholesterol, hypertension, and high fasting blood sugar. The prevalence of metabolic syndrome was just over 29 percent in men and 24.5 percent in women. The authors suggest that as the prevalence of metabolic syndrome in Korea is high, it is critical to identify modifiable risk factors such as sleep duration. The study appears in the journal BMC Public Health.