When You Snooze (Too Much Or Too Little), You Lose

Scientists in South Korea have found that insufficient or excess sleep is associated with metabolic syndrome and poor health.

AsianScientist (Jun. 22, 2018) – A research group in South Korea has found that less than six and more than ten hours of sleep per day are associated with metabolic syndrome. Their findings are reported in BMC Public Health.

How much sleep is optimal for a human being? There are known reports that lack of sleep is associated with ill health, but the precise number of hours of sleep for optimal wellbeing remains unknown. In this study, researchers at the College of Medicine, Seoul National University, studied 133,608 Korean men and women aged 40-69 years in a cross-sectional study to find an answer.

The authors used data from the HEXA study, a large-scale, community-based study conducted in Korea from 2004-2013, which included information on socio-demographic characteristics, medical history, medication use, family history, lifestyle factors, diet, physical activity and reproductive factors for women.

As part of the HEXA study, samples of plasma, serum, buffy coat, blood cells, genomic DNA and urine were collected, and participants underwent physical examinations by medical professionals. Sleep duration was assessed by asking the question: in the past year, on average, how many hours/minutes of sleep (including daytime naps) did you take per day?

The researchers 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. On the other hand, women who slept fewer than six hours were more likely to have higher waist circumference.

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.

Sleeping more than ten hours per day was associated with metabolic syndrome and increased levels of triglycerides in men. In women, sleep in excess of ten hours per day was associated with metabolic syndrome, higher waist circumference, higher levels of triglycerides and blood sugar, as well as low levels of ‘good’ cholesterol (HDL-C).

The scientists also reported that nearly 11 percent of men and 13 percent of women slept for less than six hours per day, while 1.5 percent of men and 1.7 percent of women slept for more than ten hours per day.

“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,” said Dr. Claire E. Kim of Seoul National University, who led the study.

“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.”

Although the biological mechanisms that underlie the association between sleep duration and metabolic syndrome remain unclear, several potential processes have been reported. These include elevated levels of hormones which increase appetite and caloric intake or reduce energy expenditure in people who sleep less than seven hours per day, which may lead to increased waist circumference and development of obesity.

The authors caution that the cross-sectional, observational nature of this study does not allow for conclusions about cause and effect. Estimates of sleep duration were based on self-reporting data rather than objective measures and may reflect ‘time in bed,’ actual time spent asleep or time people believed they slept. Also, as the study did not distinguish between daytime naps and nighttime sleep, their impact on health could not be assessed separately.


The article can be found at: Kim et al. (2018) Association Between Sleep Duration and Metabolic Syndrome: A Cross-sectional Study.

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Source: Biomed Central; Photo: Pexels.
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