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: p5, 6, 7, 8 and X9 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 p5 h per night, those of hyperglycemia and high triglyceridemia were highest in subjects who slept X9 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 p5 h per night demonstrated the highest risk for the metabolic syndrome (OR 1.74, 95% CI 1.33-2.26, Po0.001). Subjects who slept X9 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 ¼ 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.

Obstructive sleep apnea syndrome (OSA) has been recognized as a common health problem, and increasing obesity rates have led to further remarkable increases in the prevalence of OSA, along with more prominent cardiovascular morbidities. Though previous studies have reported an independent relationship between elevated high sensitivity C-reactive protein (hsCRP) levels and OSA, the issue remains controversial owing to inadequate consideration of obesity and various confounding factors. So far, few population based studies of association between OSA and hsCRP levels have been published. Therefore, the purpose of the present study was to investigate whether OSA is associated with increased hsCRP levels independent of obesity in a large population-based study. A total of 1,835 subjects (968 men and 867 women) were selected from a larger cohort of the ongoing Korean Genome and Epidemiology Study (KoGES). Overnight polysomnography was performed on each participant. All participants underwent anthropometric measurements and biochemical analyses, including analysis of lipid profiles and hsCRP levels. Based on anthropometric data, body mass index (BMI) and waist hip ratio (WHR) were calculated and fat mass (FM) were measured by means of multi-frequency bioelectrical impedance analysis (BIA). Mild OSA and moderate to severe OSA were defined by an AHI >5 and ≥15, respectively. The population was sub-divided into 3 groups based on the tertile cut-points for the distribution of hsCRP levels. The percentage of participants in the highest tertile of hsCRP increased dose-dependently according to the severity of OSA. After adjustment for potential confounders and obesity-related variables (BMI, WHR, and body fat) in a multiple logistic model, participants with moderate to severe OSA had 1.73-, 2.01-, and 1.61-fold greater risks of being in the highest tertile of hsCRP levels than participants with non-OSA, respectively. Interaction between obesity (BMI ≥25kg/m2) and the presence of moderate-to-severe OSA was significant on the middle tertile levels of hsCRP (OR = 2.4), but not on the highest tertile, compared to the lowest tertile. OSA is independently associated with elevated hsCRP levels and may reflect an increased risk for cardiovascular morbidity. However, we found that OSA and obesity interactively contribute to individuals with general levels of hsCRP (<1.01 mg/dl). The short-term and long-term effects of elevated hsCRP levels on cardiovascular risk in the context of OSA remain to be defined in future studies.

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