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Recently, several institutions, including the American Academy of Sleep Medicine, the Sleep Research Society, and the National Sleep Foundation, have made consensus recommendations concerning appropriate sleep duration for adults. Although numerous studies conducted in Western populations have provided evidence of the harmful effects of short or long sleep duration on mental health, it is still unclear whether these consensus recommendations are appropriate in Korean culture.
Data from 1,892 subjects with no history of medical or psychiatric diagnoses were selected from the Korea National Health and Nutrition Examination Survey of 2014. Subjects were divided into seven groups based on their sleep duration (≤4, 5, 6, 7, 8, 9, and ≥10 hours). Depressive symptoms were measured using the Patient Health Questionnaire-9 and perceived stress severity was evaluated using a Likert-type scale. Group differences in depressive symptoms and severity of stress were analyzed using an analysis of covariance.
Depressive symptoms in subjects with sleep duration of ≤4 hours (5.7±5.9) or 5 hours (3.4±3.9) were higher than in subjects with a sleep duration of 7 (2.2±2.9) or 8 hours (2.2±2.9) (corrected P<0.05). Furthermore, subjects with a short sleep duration (5 hours or below) had greater perceived stress severity than subjects with a sleep duration of 7 or 8 hours (corrected P<0.05).
Our results suggest that maintaining an appropriate sleep duration as found in the recent consensus recommendation is important for mental health, even in healthy subjects without any medical or psychiatric illnesses, in Korea.
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We examined the association between salivary mitochondrial DNA (mtDNA) copy number and chronic fatigue combined with depression and insomnia.
This cross-sectional study included 58 healthy adults with moderate to severe fatigue (Brief Fatigue Inventory [BFI] ≥4) for longer than 6 months. Subjects were classified as those without combined symptoms, with either depression (Beck Depression Inventory [BDI] ≥13) or insomnia (Pittsburgh Sleep Quality Index [PSQI] ≥5), or with both depression and insomnia. Salivary mtDNA copy number was measured by real-time quantitative polymerase chain reaction. The association was evaluated using a general linear model.
About 76% of participants had either depression or insomnia as additional symptoms. These subjects were predominately female, drank more alcohol, and exercised less than those without combined symptoms (P<0.05). The group with both depression and insomnia exhibited significantly higher BFI and lower mtDNA copy number than those without combined symptoms (P<0.05). After adjusting for confounding factors, significant negative associations between mtDNA copy number and usual fatigue were found in the group without combined symptoms, whereas the negative associations in the group with combined symptoms were attenuated. BDI and PSQI were not associated with mtDNA copy number.
Chronic fatigue is negatively associated with salivary mtDNA copy number. Salivary mtDNA copy number may be a biological marker of fatigue with or without combined symptoms, indicating that a separate approach is necessary.
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The prevalence of metabolic syndrome (MetS) has risen rapidly worldwide, including in South Korea. Factors related to lifestyle are closely associated with the development of MetS. The aim of this study was to investigate the association between MetS and a number of factors positively influencing health, namely non-smoking, low-risk drinking, sufficient sleep, regular exercise, and the habit of reading food labels, among Korean men.
This cross-sectional study included 3,869 men from the 2007–2009 Korean National Health and Nutrition Examination Survey. Information on five factors positively influencing their health was obtained using a self-reported questionnaire. We categorized subjects into four groups, depending on the number of positive factors reported (group I, 0–1 factor; group II, 2 factors; group III, 3 factors; group IV, 4–5 factors).
Men who reported a greater number of positive health factors had better laboratory and anthropometric values than men who reported fewer positive health factors. The prevalence of MetS was 29.1, 27.2, 20.7, and 14.6% in groups I to IV, respectively. Compared to group I, odds ratios (95% confidence intervals) for MetS were 0.96 (0.78–1.19) in group II, 0.67 (0.52–0.87) in group III, and 0.52 (0.35–0.76) in group IV, after adjusting for confounding factors. Odds ratios for abdominal obesity, glucose intolerance, and hypertriglyceridemia were statistically significant.
A greater number of positive lifestyle factors influencing health were associated with a lower risk of developing MetS, in a nationally representative sample of Korean men.
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Shift workers are increasing worldwide, and various negative health effects of shift work have been reported. This study aimed to evaluate the relationship between shift work and health behavior.
This cross-sectional study included a total of 11,680 Korean adults (6,061 men and 5,619 women) aged ≥20 years old who participated in the Fifth Korean National Health and Nutrition Examination Survey, 2010–2012. Multiple logistic regression analysis was performed to evaluate the association between shift work and health behavior after adjusting for covariates.
In men, shift work was associated with an increased risk of inadequate sleep (odds ratio [OR], 1.18; 95% confidence interval [CI], 1.00 to 1.40) compared to day work. In women, shift work was associated with an increased risk of smoking (OR, 1.73; 95% CI, 1.34 to 2.22) and inadequate sleep (OR, 1.24; 95% CI, 1.05 to 1.47) compared to day work. In an age-stratified subgroup analysis, female shift workers aged ≥50 years old demonstrated an increased risk of smoking (OR, 5.55; 95% CI, 3.60 to 8.55), alcohol consumption (OR, 2.22; 95% CI, 1.53 to 3.23), and inadequate sleep (OR, 1.50; 95% CI, 1.10 to 2.05) compared to female day workers.
Shift work is associated with worse health behavior, and this is most evident in women aged ≥50 years. Targeted strategies to reduce the negative health effects of shift work should be implemented, with consideration of shift workers' demographic characteristics.
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Low levels of physical activity can cause various physical symptoms or illness. However, few studies on this association have been conducted in young adults. The aim of this study was to investigate the association between physical activity levels and physical symptoms or illness in young adults.
Subjects were university students who participated in a web-based self-administered questionnaire in a university in Seoul in 2013. We obtained information on physical activities and physical symptoms or illness in the past year. Independent variables were defined as symptoms or illness which were associated with decreased academic performance. Logistic regression was performed to calculate odds ratios (ORs) and 95% confidence intervals (CIs) of each physical symptom or illness with adjustment for covariables.
A total of 2,201 participants were included in the study. The main physical symptoms or illness among participants were severe fatigue (64.2%), muscle or joint pain (46.3%), gastrointestinal problems (43.1%), headache or dizziness (38.6%), frequent colds (35.1%), and sleep problems (33.3%). Low physical activity levels were significantly associated with high ORs of physical symptoms or illness. Multivariable-adjusted ORs (95% CIs) in the lowest vs. highest tertile of physical activity were 1.45 (1.14–1.83) for severe fatigue, 1.35 (1.07–1.70) for frequent colds, and 1.29 (1.02–1.63) for headaches or dizziness. We also found that lower levels of physical activity were associated with more physical symptoms or bouts of illness.
Low physical activity levels were significantly associated with various physical symptoms or illness among university students. Also, individuals in the lower levels of physical activity were more likely to experience more physical symptoms or bouts of illness than those in the highest tertile of physical activity.
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Previous studies have revealed that sleep duration is linked to both obesity and hypertension. Here, we evaluated the association between sleep duration and hypertension in obese and non-obese premenopausal women using representative national survey data from the Korean population.
A total of 4,748 subjects over 20 years of age from the Korean National Health and Nutrition Examination Survey from 2010 to 2012 were included. To control for risk factors, multivariable logistic regression was used to calculate the adjusted odds ratios and 95% confidence intervals of hypertension across the following sleep duration categories: <6, 6-8, and >8 h/d.
Among the participants, 367 subjects (7.7%) had hypertension. Their mean sleep duration was 7 hours. In the non-obese subjects, after controlling for potential confounding variables, the odds ratio for hypertension was 1.86 fold greater in those with a sleep duration of <6 hours (odds ratio, 1.79; 95% confidence interval, 1.05 to 3.03) as compared to those who slept for 6.8 hours. However, there was no association between sleep duration and the risk of hypertension in obese subjects. Long sleep duration (over 8 h/d) was not associated with hypertension in either the non-obese or the obese subjects in this study.
Short sleep duration (less than 6 h/d) may be a significant risk factor for hypertension in non-obese premenopausal women. However, there is no association between sleep duration and the risk of hypertension in obese women.
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Impaired fasting glucose (IFG) is an established risk factor for type 2 diabetes and cardiovascular disease. This study evaluated the relationship between sleep duration and IFG.
This cross-sectional study included 14,925 Korean adults (5,868 men and 9,057 women) ≥19 years of age who participated in the Korean National Health and Nutrition Examination Survey between 2011 and 2012. Blood glucose levels were measured after at least eight hours of fasting. Study subjects were categorized into three groups based on self-reported sleep duration (<7, 7–8, or >8 h/d). IFG was diagnosed according to recommendations American Diabetes Association guidelines. Multiple logistic regression analysis was performed with adjustment for covariates.
In men, short sleep duration (<7 hours) was associated with increased risk of IFG (odds ratio [OR], 1.46; 95% confidence interval [CI], 1.08 to 1.96) compared to adequate sleep duration (7–8 hours), whereas long sleep duration (>8 hours) was not associated with risk of IFG (OR, 0.90; 95% CI, 0.37 to 2.18). In women, sleep duration was not associated with risk of IFG.
The association between sleep duration and IFG differed by sex; sleep deprivation, was associated with increased risk of IFG, especially in men.
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Alcohol is traditionally known to have a relaxing effect. However, persons who consume alcohol in excessive amounts suffer from poor sleep quality and patients with alcohol use disorders commonly report insomnia. In this study, we aimed to evaluate the effects of alcohol use on sleep quality.
A questionnaire-based cross-sectional survey was conducted with 234 men and 159 women who had visited a general hospital. We used structured questionnaires, including Alcohol Use Disorder Identification Test-Korean revised version (AUDIT-KR) and the Pittsburgh Sleep Quality Index-Korean version (PSQI-K). We analyzed the association between scores for all subcategories of the PSQI-K and the AUDIT-KR and then analyzed the correlation between AUDIT-KR and global PSQI-K scores.
The global PSQI-K score for men was positively correlated with the AUDIT-KR score (P=0.008) after adjusting for age, chronic disease, tobacco use, exercise, depression, and anxiety. The AUDIT-KR score was significantly associated with subjective sleep quality (P=0.005), sleep duration (P=0.047), and sleep disturbance (P=0.048); it was not associated with sleep latency, sleep efficiency, or daytime dysfunction. Sleep disturbances due to snoring were significantly associated with total AUDIT-KR score (P=0.008). There was no correlation between the global PSQI-K and AUDIT-KR scores for women (P=0.333). However, daytime dysfunction showed a significant association with total AUDIT-KR score (P=0.048).
Men with higher AUDIT-KR scores tended to suffer from poor sleep quality. AUDIT-KR scores showed significant correlations with subjective sleep quality, sleep duration, and sleep disturbances in men.
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The prevalence of metabolic syndrome is increasing worldwide, and previous studies have shown that inadequate sleep duration and skipping breakfast may be related to metabolic syndrome. Therefore, we investigated the effects of inadequate sleep and skipping breakfast on metabolic syndrome using data from the Korea National Health and Nutrition Examination Survey (KNHANES) IV & V reports (2007-2009 and 2010-2012, respectively).
The sample included 12,999 subjects who participated in the KNHANES IV & V. Sleep duration and breakfast eating were self-reported, and metabolic syndrome was defined according to the modified National Cholesterol Education Program Adult Treatment Panel III guidelines. Subjects were divided into 12 groups according to breakfast eating and sleep duration patterns, and multiple logistic regression analyses adjusted for age, sex, household income, education level, smoking status, alcohol drinking, physical activity, and total daily energy intake were conducted.
In subjects under 50 years of age, sleeping less than 6 hours was significantly associated with increased metabolic syndrome except among those who ate breakfast on only 1 of the past 2 days. In subjects over 50 years of age, sleeping less than 6 hours was significantly associated with a decreased risk of metabolic syndrome among those who ate breakfast on both days.
In conclusion, significant associations between metabolic syndrome and sleep duration were identified, and these associations differed according to age group.
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Neck circumference, as a predicator of obesity, is a well-known risk factor for obstructive sleep apnea and cardiovascular diseases. However, little research exists on neck length associated with these factors. This study explored the association of neck length with sleep and cardiovascular risk factors by measuring midline neck length (MNL) and lateral neck length (LNL).
We examined 240 patients aged 30 to 75 years who visited a health check-up center between January 2012 and July 2012. Patients with depressive disorder or sleep disturbance were excluded from this study. MNL from the upper margin of the hyoid bone to the jugular notch and LNL from the mandibular angle to the mid-portion of the ipsilateral clavicle were measured twice and were adjusted by height to determine their relationship with sleep and cardiovascular disease risk factors.
Habitual snorers had shorter LNL height ratios (P = 0.011), MNL height ratios in men (P = 0.062), and MNL height ratios in women (P = 0.052). Those snoring bad enough to annoy others had shorter MNL height ratios in men (P = 0.083) and women (P = 0.035). Men with objective sleep apnea had longer distances from the mandible to the hyoid bone to the mandible (P = 0.057). Men with metabolic syndrome had significantly shorter LNL height ratios (P = 0.021), and women with diabetes, hyperlipidemia, and metabolic syndrome had shorter MNL height ratios (P < 0.05).
This study shows that a short neck by measuring the MNL is probably associated with snoring. In addition, MNL is related to cardiovascular disease risk factors in women.
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An association between sleep duration and a wide spectrum of diseases has been reported, but little is known about its relationship with bone mineral density (BMD). Previously conducted studies in Korea and abroad have reported results that are controversial. The present study sought to assess whether sleep duration can be considered an independent risk factor of osteoporosis.
We included participants over the age of 60 years with data on self-reported habitual sleep duration and BMD measured with dual X-ray absorptiometry. Comprehensive data on the study sample was obtained from the Korea National Health and Nutritional Survey performed from 2008 to 2010. Sex-stratified multiple regression analyses were conducted with adjustments for possible confounding factors.
There was a significant inverse dose-dependent association between sleep duration and BMD measured at total hip, femur neck, and lumbar spine for women and total hip and femur neck for men. Sex-stratified regression analyses adjusted for age and body mass index revealed that sleep duration had a negative correlation with BMD at total hip and femoral neck for both women (β = -0.0048; P = 0.0172 for total hip, β = -0.0037; P = 0.0303 for femur neck) and men (β = -0.0057; P = 0.0218 for total hip, β = -0.0057; P = 0.0143 for femur neck). For women, the significance remained after further adjustment of confounding variables.
Prolonged sleep duration appears to have a significant association with lower total hip and femur neck BMD in elderly women but not in elderly men.
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Sleep disorder is a common problem in adults and affects physical and mental health. We investigated factors associated with poor sleep quality in Korean primary care.
A total of 129 couples (129 husbands and 129 wives) aged 30 to 79 years were included in this study from March, 2009 to February, 2010. The subjects were surveyed using a specific questionnaire. Sleep disorder was defined by a Pittsburgh Sleep Quality Index global score greater than 5 (poor sleepers). The subjects were divided into a group of good sleepers (n = 160) and a group of poor sleepers (n = 98). Socio-demographic and clinical covariates including age, sex, depression, spouse sleep disorder, and spouse depression were reported.
Poor sleep quality was present in 38.0% of total subjects. According to chi-square test results, female, patients with depression, and low sleep quality of spouse were significantly associated with sleep disorder. In multivariate logistic regression analysis, depression increased the risk of poor sleep quality (odds ratio [OR], 7.775; 95% confidence interval [CI], 2.555 to 23.661), and non-risky drinking decreased the risk of poor sleep quality (OR, 0.343; 95% CI, 0.128 to 0.924).
In our study, more than one-third of participants had poor sleep quality. Depression was a strong independent factor associated with sleep problems.
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