(A) prospective cohort study on the association of sleep characteristics with all-cause mortality in Korean adults

Abstract

Introduction: Sleep quantity and quality may independently contribute to functional deficits in various physiological mechanisms and act as a significant predictor of future complications including mortality. This study aims 1) to provide an overview of the survey items for assessing habitual sleep characteristics and to evaluate the survey items validity as a reliable measurement tool in the context of population health research in the Korean adults

2) to identify the putative covariates that might be highly intercorrelated with both sleep characteristics and mortality in the Korean adult population

and 3) to investigate whether both sleep quantity and quality may be an independent predictor for all-cause mortality and also to evaluate whether the composite sleep score covering both quantitative and qualitative evaluation of usual sleep behavior can determine the magnitude of the all-cause mortality risk in the Korean adults. Methods: Among a total of 162,142 men and women who had voluntarily participated in the Health Examinees (HEXA) study between 2004 and 2012, 158,147 participants (53,789 men and 104,358 women, aged 40?69) who provided information on both sleep duration and sleep complaints were included in the present study. Sleep duration was assessed through self-reported information that was collected by well-trained interviewers and categorized into < 6 hours (short sleep), 6?7 hours (normal sleep), 8?9 hours (moderately long sleep), and ≥ 10 hours (long sleep). Sleep complaints were estimated using two independent questions about how the study subject had felt physically and mentally in terms of insomnia: difficulty in initiating sleep and nonrestorative sleep. All cohort members were passively followed-up through record linkage to the national death certificate. A cross-sectional analysis was conducted to evaluate the putative correlates?sociodemographic factors, lifestyle factors, psychological conditions, anthropometric indices, and baseline health condition?of sleep characteristics by using multinomial logistic regression models. Moreover, Cox proportional hazards regression models were employed to estimate the relative risks for the associations of habitual sleep characteristics with all-cause mortality after taking into account for all putative correlates. Prior to the cross-sectional and cohort analyses, a preliminary validation study was conducted to assess the survey items validity and usefulness. Results: 1) Sleep survey items adopted in the HEXA study corresponded with the valid international measurement tool. Furthermore, a composite sleep score exhibited a fair predictive power to discriminate poor sleepers who might have trouble with inadequate sleep duration and/or low quality sleep from the normal healthy Korean adults. 2) Regardless of sexual differences, we found that adverse behaviors and lifestyle factors including low educational attainment, unemployment, being unmarried, current smoking status, lack of exercise, having irregular meals, poor psychosocial well-being status, frequent stress events, and poor self-rated health were significantly associated with abnormal sleep duration. 3) Both short sleep duration and frequent sleep complaints significantly increased the risk for all-cause mortality

the results were more prominently exhibited among men. Poor sleepers were at a significantly higher risk for mortality regardless of sex. Additionally, habitual sleep characteristics might be independently involved in a higher risk of all-cause mortality, yielding associations independent of confounders including underlying medical condition and health status. Conclusions: Our findings suggest that 1) survey items for assessing habitual sleep characteristics adopted in the HEXA study can be a valid tool and a composite sleep score can estimate individuals sleep status covering quantitative and qualitative evaluation of sleep behavior

2) detrimental health behaviors, low socioeconomic status and medical treatment of specific diseases might be meaningful determinants for abnormal sleep duration in Korean adults

and 3) both short and long sleep duration, as well as frequent sleep complaints can place Korean adults at an increased risk for all-cause mortality, which indicates there may be a substantial public health burden of sleep-related mortality in the Korean population. In order to encourage good physical health and psychosocial well-being, people who sleep too little or too much should be treated as at-risk populations. Furthermore, tailor-made interventions that can assist people to cope with sleep disturbances as well as maintaining adequate sleep patterns in terms of both quantity and quality is warranted to reduce the latent disease burden.