Relationship between sleep duration and the metabolic syndrome: Korean National Health and Nutrition Survey 2001

Objectives: Previous studies have revealed that both short and long sleep durations are linked to obesity, hyperglycemia and hypertension. We evaluate the relationship between sleep duration and the metabolic syndrome using representative national survey data from the Korean population. Methods: We analyzed data from the 2001 Korean National Health and Nutrition Survey. The average amount of sleep per night was categorized as: <= 5, 6, 7, 8 and >= 9 h. Those reporting 7 h per night served as a reference group. In this cross-sectional study, the data of 4222 participants were finally analyzed. Results: A majority of the components of the metabolic syndrome demonstrated U-shaped patterns based on sleep duration. Although the prevalences of abdominal obesity and hypertension were highest in subjects who slept <= 5 h per night, those of hyperglycemia and high triglyceridemia were highest in subjects who slept >= 9 h per night. Prevalence of the metabolic syndrome also exhibited U-shape pattern based on sleep duration. More components of the metabolic syndrome were highly associated with sleep duration in subjects under the age of 60 compared to those over the age of 60. Subjects who slept <= 5h per night demonstrated the highest risk for the metabolic syndrome (OR 1.74, 95% CI 1.33-2.26, P<0.001). Subjects who slept >= 9 h per night exhibited increased risk for the metabolic syndrome even after adjustment of other risk variables (OR 1.69, 95% CI 1.17-2.45, P = 0.006). Conclusions: Both short and long sleep durations are related to increased risk of the metabolic syndrome and its components in the Korean population, although adjustment for risk factors attenuates their relationship. Subjects reporting sleep duration of 7 h demonstrated the lowest prevalence of the metabolic syndrome.