Prevalence of excessive daytime sleepiness and associated factors in the adult population of Korea.

OBJECTIVE: Information on the prevalence and correlates of excessive daytime sleepiness (EDS) is limited for Asians. We determined the prevalence of EDS and its associated factors in the adult population of Korea. SUBJECTS AND METHODS: The subjects consisted of 4405 Koreans aged 40-69 years from the Korean Genome Epidemiology Study, which is an ongoing prospective population-based study. Data were collected from a comprehensive health examination and a questionnaire at baseline. RESULTS: The prevalence of EDS was 12.2% (10.7% for men and 13.7% for women). In multivariate models including sociodemographic, biochemical, clinical and sleep-related factors, age, physical activity, education, habitual snoring, waking up feeling unrefreshed, perceived insufficient sleep, and crawly feelings in the legs were significantly associated with EDS. Subjects aged 50-59 years had an excess risk of EDS by 1.42-fold (95% confidence interval [CI]=1.13-1.77) compared to those aged 40-49 years. In addition, the subjects with top quartile group of physical activity had a 1.80-fold (95% CI=1.18-2.73) higher risk of EDS than those with the lowest quartile group. A higher level of education was inversely associated with the risk of EDS. Furthermore, the subjects with habitual snoring had a 1.92-fold (95% CI=1.47-2.50) greater risk of EDS than non-snorers. Perceived insufficient sleep also increased the risk of EDS by 1.58-fold (95% CI=1.29-1.93) compared to perceived sufficient sleep. Subjects with crawly feelings in the legs had a 1.51-fold (95% CI=1.13-2.00) higher risk of EDS than those without crawly feelings in the legs. In addition, waking up feeling unrefreshed elevated a 1.24-fold (95% CI=1.01-1.53) risk of EDS compared to waking up feeling refreshed. CONCLUSIONS: Our findings show that EDS is associated with a variety of factors in Korean adults, and habitual snoring or sleep-related problems increase the risk of EDS. Whether interventions to modify associated correlates can alter EDS warrants further study.

Association of snoring with chronic bronchitis.

BACKGROUND: Snoring is more prevalent in patients with chronic bronchitis than in persons without it. Few studies have examined the effect of snoring on chronic bronchitis. We prospectively investigated the association between snoring and the incidence of chronic bronchitis. METHODS: The baseline study was conducted from June 25, 2001, to January 29, 2003. Members of the study cohort consisted of 5015 male and female Korean citizens aged 40 to 69 years at baseline who participated in a comprehensive health examination and on-site interviews at Korea University Ansan Hospital. Of these, 4270 participants (52% men and 48% women) entered the analysis for the first 2-year follow-up from April 17, 2003, to February 20, 2005, and those who met the same inclusion criteria remained in the analysis for a second 2-year follow-up period from February 21, 2005, to November 17, 2006. We collected information on snoring at baseline and identified incident cases of chronic bronchitis during a 4-year follow-up period. On the baseline questionnaire, we excluded participants who reported the presence of cough and sputum production on most days for at least 3 months a year. RESULTS: During 4 years of follow-up, we documented 314 cases of new-onset chronic bronchitis (27.1 cases per 1000 person-years). After taking into account age, smoking, and other risk factors for chronic bronchitis, the multivariate relative risks of chronic bronchitis were 1.25 (95% confidence interval [CI], 0.95-1.64) for persons snoring 5 times per week or less and 1.68 (95% CI, 1.17-2.42) for those snoring 6 to 7 times per week compared with never snorers (P for trend = .049). The analyses stratified by risk factors, including smoking, occupation, and body mass index, showed a stronger association among never smokers, house workers, and overweight persons. In analysis for the joint effect of smoking and snoring, the relative risks of chronic bronchitis were 1.39 (95% CI, 1.01-1.90) for nonsmoking and snoring, 2.31 (95% CI, 1.38-3.87) for smoking and never snoring, and 2.86 (95% CI, 1.91-4.27) for smoking and snoring compared with nonsmoking and never snoring. CONCLUSIONS: This prospective study observed that snoring is associated with chronic bronchitis. Our findings provide support for the hypothesis that snoring influences the development of chronic bronchitis.

Short-term incidence rate of hypertension in Korea middle-aged adults.

OBJECTIVES: Despite recent increasing trends in cardiovascular morbidities and mortality in Asia, studies on short-term changes in cardiovascular risks remain limited. This study estimated 2-year incidence rates of hypertension in middle-aged Korean adults aged 40-69 years, and investigated the impact of baseline levels of blood pressure, body mass index, and other conventional risk factors on the progression to hypertension. METHODS: Blood pressures of participants were evaluated twice with a 2-year interval, measured by mercury sphygmomanometer according to the standardized protocol. Hypertension was defined when either the systolic and diastolic blood pressures were greater than 140 and 90 mmHg, respectively, or when a participant was treated with antihypertensive medications. RESULTS: The crude 2-year incidence (calculated per 100) of hypertension was 12.2; 13.0 for men and 11.6 for women. For those who had higher blood pressure at baseline examination, incidence rates were two-fold or five-fold higher compared with those with optimal blood pressure. Older age and overweight were also major predictors for hypertension, even in Koreans with a low serum cholesterol level. CONCLUSION: This is the first investigation of short-term incidence rates of hypertension in Asia. The results are consistent with the recently reported increasing trends in cardiovascular mortality and morbidity in Asia.

Relation of habitual snoring with components of metabolic syndrome in Korean adults.

AIMS: To examine the association between habitual snoring and components of the metabolic syndrome in Korean adults. Whether these associations are independent of obesity was also explored. METHODS: Four thousand five hundred and six men and 5041 women aged 40-69 years from the Korean Health and Genome Study were examined. Information of snoring frequency was obtained by a questionnaire and components of the metabolic syndrome were measured. RESULTS: There was a clear dose-response relationship between the increasing frequency of snoring and the higher prevalence of each component of the metabolic syndrome (P<0.001). After adjustment for age, abdominal obesity, and the other metabolic components, hypertension was significantly associated with a 1.2-fold excess of habitual snoring in both men (P<0.05) and women (P<0.05). The association of habitual snoring with hypertension was unaltered by obesity. Regardless of the presence or absence of abdominal obesity, there was an increase in the prevalence of habitual snoring as the number of metabolic abnormalities increased. CONCLUSIONS: Habitual snoring is associated with hypertension independent of obesity. While the relationship between habitual snoring and obesity is well recognized, characterization of the role of the other components of the metabolic syndrome as a cause or result of habitual snoring warrants a further study.

Prevalence and correlates of habitual snoring in high school students.

STUDY OBJECTIVES: To examine the prevalence and correlates of habitual snoring in senior high school students in Korea. DESIGN: A cross-sectional survey. SETTING: Ten high schools in the southern part of Seoul, Korea. PARTICIPANTS: A total of 3,871 high school students (2,703 male students and 1,168 female students; age range, 15 to 18 years; mean age: male students, 16.8 years; female students, 16.9 years) who were attending the 11th grade. MEASUREMENTS AND RESULTS: Data were collected on sociodemographic characteristics, school performance, and patterns of sleep and sleep-related disturbances. The overall prevalence of habitual snoring was 11.2% (boys, 12.4%; girls, 8.5%). The mean total sleep time was similar in habitual snorers vs nonsnorers (6.4 and 6.3 h per day, respectively). Frequency of snoring increased significantly with body mass index (BMI) [p < 0.001], cigarette smoking (p < 0.01), prevalence of witnessed apnea (p < 0.001), and Epworth sleepiness scale score (p < 0.001). The frequency of snoring increased with a decline in school performance (p < 0.001). For those whose school performance was low, there was a 35% excess in the odds of habitual snoring vs those whose school performance was high (odds ratio, 1.35; 95% confidence interval, 1.01 to 1.78). CONCLUSIONS: These findings suggest that chronic habitual snoring is associated with multiple factors in adolescents. Whether interventions to modify BMI and smoking can alter snoring habits and related clinical problems warrants further study, particularly as it also may improve academic performance in high school students.

Association between C-reactive protein and QTc interval in middle-aged men and women.

BACKGROUND: Both of prolonged QT interval and elevated C-reactive protein (CRP) levels are known to be risk factors of cardiovascular disease. To our knowledge, few studies have reported the direct relationship between CRP levels and the QT interval in middle-aged population. The objective of the present study was to examine the association of CRP level with QT interval. METHODS AND RESULTS: A total of 2471 men and 2287 women from the Korea n Health and Genome study underwent physical examination and completed a questionnaire. A 12-lead electrocardiogram (ECG) recording was obtained from each subject. Subjects who were taking statins, non-steroidal anti-inflammatory drugs (NSAID) and postmenopausal hormone replacement therapy, which are known to have an effect on CRP levels, were excluded. Geometric means of CRP levels were compared among three groups, which were classified by heart rate-corrected QT (QTc) interval: prolonged (> or =440 msec in men and > or =450 msec in women), borderline (420-439 msec in men and 430-449 msec in women) and normal (<420 msec in men and <430 msec in women) groups. The means of CRP level in women, though over normal range, increased significantly as QTc interval was longer, independent of confounding factors, while those of men were on the borderline of significance. However, compared to normal range of QTc interval, prolonged QTc interval was associated with elevated CRP level, defined as more than 95 percentile of CRP, in men and women, respectively. CONCLUSIONS: Prolonged QTc interval in middle-aged men and women is associated with the elevated CRP, independent of confounding factors.

Habitual snoring is associated with elevated hemoglobin A1c levels in non-obese middle-aged adults.

Hemoglobin A(1c) (HbA(1c)) is an indicator of long-term glycemic control. The purpose of this study was to determine whether habitual snoring is associated with increased HbA(1c) levels in non-obese and normoglycemic middle-aged men and women. A total of 6981 subjects (3362 men and 3619 women) aged 40-69 years from the Korean Health and Genome Study were examined for the study. Each participant received a comprehensive physical examination as well as a set of questions pertaining to demographic characteristics and snoring frequency. Habitual snoring was defined as a snoring frequency of > or = 4 days week(-1). After adjusting for age, abdominal obesity, and other confounding covariates, male habitual snorers showed a 1.69-fold excess [95% confidence interval (CI) 1.30-2.19] odds of having a high HbA(1c) level. Similarly, premenopausal women with habitual snoring had a 2.31 times (95% CI 1.22-4.39) significantly higher odds of having elevated HbA(1c)levels compared with non-snorers. This association was not found in postmenopausal women. Multivariate analysis revealed that male habitual snorers aged 40-50 had a 2.08-fold excess (95% CI 1.40-3.09) risk of having an elevated HbA(1c) level. In male habitual snores over 50, the strength of association was attenuated. Our findings based on cross-sectional data support a hypothesis that habitual snoring is associated with impaired glucose tolerance even in non-obese and normoglycemic men and premenopausal women. However, as waist circumference as an index of abdominal obesity (visceral adiposity) in the present study may only partially represent the effect of visceral fat, there may be a residual confounding from visceral obesity in our result. Longitudinal follow-up studies are necessary to confirm the association between sleep-disordered breathing and impaired glucose tolerance and to examine the causal relationship in a healthy population without obesity and diabetes.

Prevalence and correlates of excessive daytime sleepiness in high school students in Korea.

The purpose of the present study was to determine the prevalence of excessive daytime sleepiness (EDS) and its associations with sleep habits, sleep problems, and school performance in high school students in South Korea. A total of 3871 students (2703 boys and 1168 girls with a mean age of 16.8 years and 16.9 years, respectively) aged 15-18 years in the 11th grade of high school completed a questionnaire that contained items about individual sociodemographic characteristics, sleep habits, and sleep-related problems. The overall prevalence of EDS was 15.9% (14.9% for boys and 18.2% for girls). Mean reported total sleep time was similar in EDS and non-EDS (6.4 +/- 1.6 and 6.4 +/- 1.3 h/day, respectively). The increased risk of EDS was related to perceived sleep insufficiency (P < 0.001), teeth grinding > or = 4 days/week (P < 0.001), witnessed apnea > or = 1-3 days/week (P < 0.01), nightmares > or = 4 days/week (P < 0.05), low school performance (P < 0.01), and two or more insomnia symptoms (P < 0.05). Students with low school performance had a 60% excess in the odds of EDS compared to those whose school performance was high. These findings suggest that EDS is associated with multiple sleep-related factors in adolescents. Whether interventions to modify associated correlates can alter EDS warrants consideration, especially because it may also improve academic performance in high school students.

Association of habitual snoring with glucose and insulin metabolism in nonobese Korean adult men.

Habitual snoring is associated with cardiovascular morbidity and mortality, and metabolic abnormalities such as impaired glucose homeostasis. Many studies were performed in obese Western populations. The purpose of this study was to examine the association of habitual snoring with glucose and insulin metabolism in nonobese Korean men who were free of diabetes and hypertension. A total of 2,719 men ages 40-69 years from the Korean Health and Genome Study participated in this study. Information of snoring frequency was obtained by a questionnaire and glucose and insulin levels during oral glucose tolerance test were measured. Repeated measures analysis of variance detected significant differences in the changing patterns of glucose and insulin levels at 1 hour and 2 hours between habitual snorers and nonhabitual snorers, whereas there were no significant differences in fasting blood glucose and insulin levels. Multivariate logistic regression analyses revealed that habitual snoring was independently associated with elevated 1-hour and 2-hour glucose levels and a 2-hour insulin level, respectively. The present data suggest that habitual snoring may affect glucose-insulin metabolism, independent of diabetes and hypertension, even in nonobese Korean middle-age men. Further prospective studies are needed to examine the causal relationship between habitual snoring and insulin resistance or glucose intolerance.

Sleep habits, excessive daytime sleepiness and school performance in high school students.

A questionnaire survey was carried out to examine the sleep habits and excessive daytime sleepiness (EDS) of 3871 high school students with a mean age of 16.8 years in Korea. The results showed that mean total sleep time was 6.3 h/day for male students and 6.5 h/day for female students, which may be insufficient for adolescence during puberty. The overall prevalence of EDS (defined as an Epworth sleepiness scale score of >10) was 15.9% (14.9% for boys and 18.2% for girls). The prevalence of EDS increased significantly (P < 0.001) with a decline in school performance.