Hyeryeon Yi

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

Abstract  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 ≥ 4 days/week (P < 0.001), witnessed apnea ≥1–3 days/week (P < 0.01), nightmares ≥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.

Prevalence of insomnia and its relationship to menopausal status in middle-aged Korean women

Abstract  Although the prevalence of insomnia and the association of insomnia with menopause have been well reported, not much work has been conducted in population‐based research on insomnia and menopause in Korea. The purpose of the present report was to determine overall and different prevalence of insomnia by menopausal status, and the relationship between insomnia and menopause in a population‐based sample of middle‐aged Korean women. A total of 96.1% of 2497 randomly selected middle‐aged Korean women participated. Insomnia was defined as occurring three times a week or more in the previous month. Subjects were categorized into three groups: premenopaues, perimenopause, and postmenopause. The overall prevalence of insomnia in middle‐aged Korean women was 14.3%. The most common symptom of insomnia was difficulty maintaining sleep (9.7%), followed by difficulty initiating sleep (7.9%), and early morning awakening (7.5%). Multiple logistic regression analysis revealed that menopause was independently associated with insomnia after adjusting for confounding factors such as age, income, and depression. Perimenopause was significantly associated with a dramatic increase in the risk of insomnia, but there was no significant association for postmenopause. The major finding is that insomnia is significantly associated with the menopausal transition. The prevalence of insomnia increases significantly by the transition from premenopause to perimenopause, but not to postmenopause. A further prospective study is needed to investigate the influence of menopause on insomnia.

Development of the Sleep Quality Scale

Sleep quality affects health and the overall quality of life. As the factors that influence sleep quality and their relative importance vary among individuals, a self‐report method is essential. Although various questionnaires have been used to assess sleep quality, few all‐inclusive assessment scales have been developed. Therefore, the purpose of this study was to develop an instrument for measuring sleep quality and to study its validity and reliability. A Sleep Quality Scale (SQS) was developed using item analysis and factor analysis on items with content validity. SQS, composed of 28 items and six factors, accounted for 62.6% of the total variance. The difference of SQS score between insomniacs and normal subjects confirmed the construct validity (t = −13.8, P = 0.000). Concurrent validity was identified by the significant correlation of SQS with the Pittsburgh Sleep Quality Index (r = 0.72, P = 0.000). The Cronbachs alpha coefficient was 0.92 for internal consistency and the correlation coefficient was 0.81 for test–retest reliability at a 2‐week interval. The developed SQS was therefore confirmed to be a valid and reliable instrument for the comprehensive assessment of sleep quality.

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.

Determining optimal sleep position in patients with positional sleep-disordered breathing using response surface analysis.

A lateral position (LP) during sleep is effective in reducing sleep disorder symptoms in mild or moderate sleep apnea patients. However, the effect of head and shoulder posture in LP on reducing sleep disorders has not been reported. In this study, effective sleeping positions and a combination of sleep position determinants were evaluated with respect to their ability to reduce snoring and apnea. The positions evaluated included the following: cervical vertebrae support with head tilting (CVS‐HT), scapula support (SS), and LP. A central composite design was applied for response surface analysis (RSA). Sixteen patients with mild or moderate positional sleep apnea and snoring who underwent polysomnography for two nights were evaluated. Based on an estimated RSA equation, LP (with a rotation of at least 30°) had the most dominant effect [P = 0.0057 for snoring rate, P = 0.0319 for apnea–hypopnea index (AHI)]. In addition, the LP was found to interact with CVS‐HT (P = 0.0423) for snoring rate and CVS‐HT (P = 0.0310) and SS (P = 0.0265) for AHI. The optimal sleep position reduced mild snoring by more than 80% (i.e. snoring rate in the supine position was <20%) and the snoring rate was approximately zero with a 40° rotation. To achieve at least 80% reduction of AHI, LP and SS should be >30° and/or 20 mm respectively. To determine an effective sleep position, CVS‐HT and SS, as well as the degree of the LP, should be concurrently considered in patients with positional sleep apnea or snoring.

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.

Tae-Eum Type as an Independent Risk Factor for Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is prevalent and associated with several kinds of chronic diseases. There has been evidence that a specific type of Sasang constitution is a risk factor for metabolic and cardiovascular diseases that can be found in patients with OSA, but there are no studies that address the association between the Sasang constitution type (SCT) and OSA. The purpose of this study was to investigate the association between the SCT and OSA. A total of 652 participants were included. All participants were examined for demographic information, medical history, and completed an interviewer-administered questionnaire on life style and sleep-related variables. Biochemical analyses were performed to determine the glucose and lipid profiles. An objective recording of OSA was done with an unattended home PSG using an Embla portable device. The apnea-hypopnea index (AHI) and oxygen desaturation index (ODI) were significantly higher in the Tae-eum (TE) type as compared to the So-eum (SE) and the So-yang (SY) types. Even after adjusting for confounding variables, the TE type still had a 2.34-fold (95% CI, 1.11–4.94; P = 0.0262) increased risk for OSA. This population-based cohort study found that the TE constitutional type is an independent risk factor for the development of OSA.

Validity and reliability of Sleep Quality Scale in subjects with obstructive sleep apnea syndrome

OBJECTIVE The present study aimed to evaluate the validity and reliability of Sleep Quality Scale (SQS) in subjects with obstructive sleep apnea syndrome (OSAS). METHODS The known group technique was used for construct validity. The study sample was composed of 40 persons with OSAS and 37 normal subjects. OSAS was defined as an apnea-hypopnea index (AHI) of > or =5 plus an Epworth Sleepiness Scale (ESS) score of >10. Control group was composed of subjects who had no history of depression and sleep problems as identified by self-report and polysomnography. A Cronbachs alpha coefficient was used for internal consistency. RESULTS The total SQS score of the OSAS subjects was significantly higher than that of the normal subjects. The SQS score homogeneity was high with a Cronbachs alpha coefficient of 0.90 in all subjects, 0.87 in the OSAS subjects, and 0.70 in the normal subjects. CONCLUSION SQS was confirmed to be an instrument with validity and high reliability for measuring sleep quality in OSAS subjects.

So-Eum Type as an Independent Risk Factor for Irritable Bowel Syndrome: A Population-Based Study in Korea

OBJECTIVES It has been hypothesized that Sasang constitutional types (SCTs) have a specific hypoactive organ, which can account for vulnerability to related diseases or symptoms. This study examined the relationship between SCTs and irritable bowel syndrome (IBS). DESIGN Cross-sectional study in a population-based cohort study in Korea. PARTICIPANTS 1362 individuals (705 men and 657 women) who participated in the Korean Genome and Epidemiology Study. OUTCOME MEASURES The participants were classified into SCTs by the integrated diagnostic model and asked about symptoms related to IBS using the Rome II criteria. RESULTS The prevalence of IBS differed significantly among the SCTs, with 33 (18.3%) of the So-eum (SE) type, 74 (9.9%) of the Tae-eum (TE) type, and 57 (13.2%) of the So-yang (SY) type having IBS. Even after adjustment for possible confounders, the SE type for both sexes continued to show 1.82-fold (95% confidence interval [CI], 1.05-3.16) excess odds of having IBS. Men with SE type had a 2.97 times (95% CI, 1.34-6.58) and a 2.50 times (95% CI, 1.15-5.47) significantly higher odds of having IBS than the TE and SY types, respectively. In analysis for the joint effect of SCT and psychological stress, the multivariate odds ratio of IBS was 3.21 (95% CI, 1.33-7.75) for the SE type and Psychological Well-Being Index-Short Form (PWI-SF) score (<27), and 5.83 (95% CI, 1.80-18.88) for the SE type and PWI-SF (≥27) compared with the TE type and PWI-SF score (<27). CONCLUSIONS The SE type of SCT is an independent risk factor for IBS. The findings support the hypothesis that persons with SE type are vulnerable to gastrointestinal diseases.