Cristina Frange1; Sandra Souza de Queiroz1,2; Juliana Martuscelli da Silva Prado2; Sergio Tufik1; Marco Túlio de Mello1,2
PURPOSE: To review the association between sleep duration and self-rated health.
METHODS: A search for original and review articles focusing on sleep duration and self-rated health was performed in PubMed. The general search strategy was [(“sleep duration” OR “total sleep time” OR “time in bed”) AND “self-rated health”].
RESULTS: We found 22 articles in the English language; 8 articles with no direct association between sleep duration and self-rated health were excluded. Of these articles, 14 were considered potentially relevant and examined in detail, and 9 were excluded for not having self-rated health as the primary outcome. This work was compounded by 5 papers. The extremes of sleep duration (short or long) exhibited an interaction with poor or worse selfrated health.
CONCLUSION: The sleep duration issue should be considered when inquiring about health conditions, as this factor can lead to adverse results in global health status.
Keywords: Sleep, Sleep duration (SD), Health, Self-rated health (SRH)
Sleep duration (SD) is a predictor of an individual's health status. Insufficient sleep is a common characteristic in our 24 h/7 days a week modern society and can lead to metabolic dysfunction, obesity, hypertension, heart attack, stroke  and coronary heart disease . On the other hand, there is conflicting evidence that we are not as deprived of sleep as we think we are; because in some countries, people are sleeping more [3,4]. However, sleep duration figures as an important outcome, while its extremes (short or long sleep) may be hazardous and might result in type 2 diabetes mellitus [5,6], increased mortality hazard , coronary heart disease, cardiovascular disease, stroke , obesity  and other comorbidities/impairments. These problems are frequently associated with short and long sleepers. As one of the major problems in our society, shortened sleep, or insufficient sleep, is a public health concern. Currently, short and long sleepers exhibit increased mortality rates, independent of sleep duration [10,11]. Studies on sleep have traditionally examined the effects of perceived sleep duration and its impact on health.
Self-rated health (SRH) is a subjective perception and has become an increasingly common measure for public health monitoring. SRH is a strong independent predictor of mortality after accounting for objective health status, behavioral risk factors and socio-demographic characteristics, and it also provides a suitable and inexpensive method of assessing an individual's health . Various socio-demographic, health and lifestyle determinants of SRH have been identified in different populations. Epidemiological studies from different societies and cultures have shown that SRH is a valid and consistent predictor of cardiovascular disease and overall mortality . The incidences of chronic diseases such as obesity, hypertension, diabetes and dyslipidemia rise significantly as SRH decreases . Variations in general SRH status are observed as a result of changes in sleep duration on morbidity and mortality .
Although 3 meta-analyses have concluded that both short and long sleep duration were associated with an increased risk of mortality and also showed greater effects on long sleepers [6,8,16], sleep duration seems to reflect comorbidity and health status. Few studies have considered the relationship between sleep duration and self-rated health in detail. Therefore, the purpose of this study was to review the association between sleep duration and self-rated health.
A search for original and review articles focusing on SD and SRH was performed in PubMed. The general search strategy was [("sleep duration” OR "total sleep time” OR "time in bed”) AND "self-rated health”]. No filters were used. Titles and abstracts were independently reviewed by the authors (CF and SSQ) against the inclusion and exclusion criteria. The inclusion criteria were the association between SD and SRH in adults and/or elderly with no specific disease and SRH as the main outcome. The full-text article was read when the abstracts were unclear. All articles were in English. The reference lists of the identified articles were also searched for additional papers. The search was conducted until January 2014.
We found 22 articles in English. Fig. 1 depicts the steps used to reach the final result. The associations of SD on SRH are shown in Table 1. In all 5 articles, the extremes of SD exhibited an interaction with poor or worse SRH, and all articles utilized self-administered questionnaires.
This review shows that SD is associated with poor or worse SRH. Short and long SD are associated with important health endpoints such as general mortality .
A retrospective observational study assessed the relationship between SD and SRH in young adults in 24 countries  and indicated a dose-response relationship, as those who slept less than 7 h were more likely to be in the poor health category. The association between short sleep (6-7 h in this study) and poorer SRH is intriguing. Despite the fact that short sleep might be due to cultural and social reasons, genetic aspects may also interfere with short SD. For example, objective short sleep duration may be a biological marker for a genetic predisposition to chronic insomnia .
As most of the studies include a heterogeneous group, it is possible to have individuals who are not sleeping enough with a wide range of sleep insufficiency and its consequences [19,20], as well as individuals with a lower physiological need for sleep . Therefore, it seems beneficial to distinguish between short sleepers and insufficient sleepers, who are often deprived of and/or restricted from sleep. Additionally, the direction of causality cannot be established: does shorter SD lead to poor SRH or does poor SRH cause shorter sleep? In the aforementioned Steptoe et al. study , it seems less likely that poor health causes shorter SD, as the investigation was performed using health subjects, suggesting the existence of underlying factors that possibly cause shorter SD and poorer SRH. Additionally, both possibilities can be associated with socioeconomic background, physical activity, body weight , health habits, mental health condition , mood changes, sleep disturbances  and genetic factors [20,24], as these analyses were controlled/adjusted for some of these factors.
In a study of more than 377,000 participants aged 18 years or older, Geiger et al.  used logistic regression models to calculate the odds ratio of the SRH associated with increasing categories of insufficient rest/sleep. They found a positive association between increasing categories of insufficient sleep and poor SRH, independent of relevant covariates. The presence of a positive dose-response trend and the persistence of the association in stratified analyses by subgroups from potential confounders, such as gender, age, BMI, and race-ethnicity, suggest that these findings are not due to chance. These results suggest that poor SRH may be an indirect mediator of the association between insufficient sleep, cardiovascular disease and mortality, and selfreported insufficient rest/sleep appears to be a strong predictor of SRH. Kim et al.  found an association between short and long SD and poor SRH in the adjusted analyses in a large representative sample of the Korean adult population.
Conversely, short and long SD could be a result of poor SRH. One third of the older adult population has extreme SD (short or long) and presents difficulties in sleep onset and maintenance or has daytime sleepiness [7,26]. A prospective observational study of adults ages 40-64 found no evidence that SD is associated with SRH in either subjective or actigraphic measures .
Studies involving middle-aged and elderly participants have documented adverse effects for both short and long SD, although they are related to different health outcomes [28,29]. In this review, we found the SD-SRH interaction in 2 studies with this population [22,30], suggesting that long SD predicts worse SRH.
Magee et al.  stratified the analysis by age and found that for participants between the ages of 45 and 74 years, short (<6 h) and long (≥ 9 h) sleep were associated with SRH; participants aged 75-84 had only long sleep associated with SRH in the adjusted analysis; and finally, participants between the ages of 85 and 97 did not show these correlations even in the unadjusted models. In fact, while much is known about the negative impacts in insufficient sleep, very little is known about the risks associated with long sleep duration.
Long sleep is defined as a habitual sleep length of at least 9 h, except hypersomnia as a clinical condition, and a long sleep duration may be associated with an increased mortality hazard caused by factors such as sleep fragmentation (excessive time in bed, wake after sleep onset and delayed sleep latency); fatigue and lethargy; immune function (long sleep may influence the increase of cytokine expression); photo-periodic abnormalities (long periods of time in a darkened environment); lack of challenge (longer time in bed provides fewer opportunities for experiencing stressors, offering physiological changes); and depression or underlying disease process (sleep apnea, heart disease, failing health). Additionally, these factors may also be related to each other .
In a self-reported habitual long sleep duration study in the Nurses Health Study II, Patel et al.  found that long sleepers reported an increased likelihood of a history of depressive symptoms, antidepressant use, benzodiazepine use, lack of physical activity, never married or divorced status, living alone, lower income, unemployed status and lower social status. Finally, mortality risks of long sleepers may be associated with general failing health. Specifically, Kakizaki et al.  found an association between stroke mortality and SRH in long sleepers. In this sense, the possibility of poor health leading to longer sleep duration seems more plausible than the alternative. Long sleep is more prevalent in those over 60 years old , thus leading to excessive daytime sleepiness . On the other extreme, Steptoe and colleagues  expected that SD>8 h would have poorer SRH, but no significant associations were found in this group or even in the very long sleeper group (>10 h).
Subjective reports of sleep time are often inaccurate. Selfrated SD modestly corresponds with more objective measurements of sleep involving polysomnography and/or actigra-phy, and there is evidence that some individuals overestimate their SD . There is evidence in the literature showing that self-assessments of health are often mistaken  and may not be suitable for tracking changes in population health over time . On the other hand, self-reported SD is well documented and a reliable measure. SD is an issue commonly used as a subjective sleep measure and is assessed by asking participants a simple question (e.g., "On average, how many hours of sleep do you have in a 24 hour period?”) and categorizing the response into groups (≤ 5 h, 6 h, 7 h, 8h, ≥ 9 or 10 h) [37-39]. SRH is often measured by a single question (e.g., "In general, how would you say that your health is?”), and the respondents choose an option from a Likert scale that consists of five levels (poor, fair, good, very good or excellent). SRH provides an important and valid indicator of an individual's health status and associated health outcomes [40,41]. We cannot disregard the fact that self-reported or perceived variables/measures could be biased due to its subjectivity because some participants may have a different understanding of the categories of answers.
The International Classification of Sleep Disorders defined short sleep as ≤5 h and long sleep as z 9 h . However, the categories of self-rated SD used by NSF Poll 2013  are different from those found in the current literature, which interfere with accurate comparisons. In Table 1, we depict different categories of SD found in the studies, which could lead to mistaken interpretations of data.
Furthermore, in future studies, sleep quality should be assessed along with the interest variables described in this paper. Distinguishing between sleep quality and SD in the context of health is quite important. A previous study reported a moderate positive correlation between overall self-rated sleep quality and average nightly sleep duration. They also showed that a better quality of sleep was associated with higher family income, but not with higher levels of education, suggesting that more education could possibly improve the quality of people's sleep . Thus, poor sleep quality is predictive of worse health . Additionally, sleep quality was more commonly reported by respondents who are more highly educated, have greater family incomes, exhibit fewer symptoms of non-specific psychological distress and are in better physical health. Sleep quality was also more commonly reported by respondents who are older, married, had fewer children, were more highly educated, employed, experiencing little financial hardship and in good physical health . In addition to being associated with better health , sleep quality was considered a stronger and more consistent predictor of mental and physical health .
Specifically about mental health, depression is known to influence both the quality and duration of sleep , and this issue is also presented as a covariate in two other studies [12,25] in this review. However, comparisons are not possible due to different methods used. The findings of these 3 studies [12,17,25] shows that even adjusting for depression in the statistical analysis, extreme SD established a close association with poorer SRH and also a higher prevalence of depression was noted in people with SD>9h . Magee  and Kakisaki  investigations pointed out that regardless emotional issues, SD can contribute to worse SRH and also worse quality of life. Again, no comparison is feasible as the methods of collection and classification of this clinical condition are different between the studies, becoming a limitation in our review. Thus the depressive symptom is undoubtedly one of the potential confounders of the presented analysis and should be considered separately in future studies and further investigated.
In summary, our results indicate the importance of using SD and SRH as predictors of diseases (physical, mental, emotional) which can result in the implementation of accessible and less expensive health programs, especially prevention programs that are able to raise the awareness of the population, as well as preventive measures to change life habits (e.g., sleep hygiene).
In this review we found that both short and long SD had prominent negative impacts on SRH, indicating an association between SD and SRH even when the adjusted analysis for possible confounders was performed. The sleep duration issue should be considered together with inquiries about health conditions, as this factor can lead to adverse results in global health status.
 Altman NG, Izci-Balserak B, Schopfer E, Jackson N, Rattanaumpawan P, Gehrman PR, et al. Sleep duration versus sleep insufficiency as predictors of cardiometabolic health outcomes. Sleep Med 2012;13:1261-70.
 Hoevenaar-Blom MP, Spijkerman AM, Kromhout D, van den Berg JF, Verschuren WM. Sleep duration and sleep quality in relation to 12-year cardiovascular disease incidence: the MORGEN study. Sleep 2011;34:1487-92.
 Bin YS, Marshall NS, Glozier N. Sleeping at the limits: the changing prevalence of short and long sleep duration in 10 countries. Am J Epidemiol 2013;177:823-33.
 Horne J. The end of sleep: “Sleep debt” versus biological adaptation of human sleep to waking needs. Biol Psychol 2011;87:1-14.
 Yaggi HK, Araujo AB, McKinlay JB. Sleep duration as a risk factor for the development of type 2 diabetes. Diabetes Care 2006;29:657-61.
 Cappuccio FP, D’Elia L, Strazzullo P, Miller MA. Quantity and quality of sleep and incidence of type 2 diabetes. Diabetes Care 2010;33:414-20.
 Kripke DF, Garfinkel L, Wingard DL, Klauber MR, Marler M. Mortality associated with sleep duration and insomnia. Arch Gen Psychiatry 2002;59:131-6.
 Cappuccio FP, Cooper D, D’Elia L, Strazzullo P, Miller MA. Sleep duration predicts cardiovascular outcomes: a systematic review and meta-analysis of prospective studies. Eur Heart J 2011;2:1484-92.
 Cappuccio FP, Taggart FM, Kandala NB, Currie A, Peile E, Stranges S, et al. Meta-analysis of short sleep duration and obesity in children and adults. Sleep 2008;31:619-26.
 Grandner MA, Hale L, Moore M, Patel NP. Mortality associated with short sleep duration: the evidence, the possible mechanisms, and the future. Sleep Med Rev 2010;14:191-203.
 Grandner MA. Sleep duration across the lifespan: implications for health. Sleep Med Rev 2012;16:199-201.
 Shankar A, Charumathi S, Kalidindi S. Sleep duration and self-rated health: the national health interview survey 2008. Sleep 2011;34:1173-7.
 Geiger SD, Sabanayagam C, Shankar A. The relationship between insufficient sleep and self-rated health in a nationally representative sample. Hindawi Publishing Corporation, J Environ Public Health 2012;2012: AID: 518263, 8 pages, http://dx.doi.org/10.1155/2012/518263.
 Yamada C, Moriyama K, Takahashi E. Self-rated health as a comprehensive indicator of lifestyle-related health status. Environ Health Prev Med 2012;17:457-62.
 Stranges S, Dorn JM, Shipley MJ, Kandala NB, Trevisan M, Miller MA, et al. Correlates of short and long sleep duration: a cross-cultural comparison between the United Kingdom and the United States: the Whitehall II Study and the Western New York Health Study. Am J Epidemiol 2008;168:1353-64.
 Gallicchio L, Kalesan B. Sleep duration and mortality: a systematic review and meta-analysis. J Sleep Res 2009;18:148-58.
 Steptoe A, Peacey V, Wardle J. Sleep duration and health in young adults. Arch Intern Med 2006;166:1689-92.
 Vgontzas AN, Fernandez-Mendoza J, Liao D, Bixler EO. Insomnia with objective short sleep duration: the most biologically severe phenotype of the disorder. Sleep Med Rev 2013;17:241-54.
 Grandner MA, Patel NP, Gehrman PR, Perlis ML, Pack AI. Problems Associated with short sleep: bridging the gap between laboratory and epidemiological studies. Sleep Med Rev 2010;14:239-47.
 Grandner MA, Pack AI. Sleep disorders, public health, and public safety. J Am Med Assoc 2011;306:2616-7.
 Aeschbach D, Sher L, Postolache TT, Matthews JR, Jackson MA, Wehr TA. A Longer biological night in long sleepers than in short sleepers. J Clin Endocrinol Metab 2003;88:26-30.
 Magee CA, Caputi P, Iverson DC. Relationships between selfrated health, quality of life and sleep duration in middle aged elderly Australians. Sleep Med 2011;12:346-50.
 Rod NH, Vahtera J, Westerlund H, Kivimaki M, Zins M, Goldberg M, et al. Sleep disturbances and cause-specific mortality: results from the GAZEL cohort study. Am J Epidemiol 2010;173:300-9.
 Carskadon MA, Sharkey KM, Knopik VS, McGeary JE. Short sleep as an environmental exposure: a preliminary study associating 5-HTTLPR genotype to self-reported sleep duration and depressed mood in first-year university students. Sleep 2012;35:791-6.
 Kim JH, Kim KR, Cho KH, Yoo KB, Kwon JA, Park EC. The association between sleep duration and self-rated health in the Korean general population. J Clin Sleep Med 2013;9:1057-64.
 Faubel R, Lopez-Garcia E, Guallar-Castillon P, Balboa-Castillo T, Gutierrez-Fisac JL, Banegas JR, et al. Sleep duration and health-related quality of life among older adults: a population-based cohort in Spain. Sleep 2009;32:1059-68.
 Jean-Louis G, Kripke DF, Ancoli-Israel S. Sleep and quality of well-being. Sleep 2000;23:1115-21.
 Heslop P, Smith GD, Metcalfe C, Macleod J, Hart C. Sleep duration and mortality: the effect of short or long sleep duration on cardiovascular and all-cause mortality in working men and women. Sleep Med 2002;3:305-14.
 Gangwisch JE, Heymsfield SB, Boden-Albala B, Buijs RM, Kreier F, Pickering TG, et al. Short sleep duration as a risk factor for hypertension: analyses of the first National Health and Nutrition Examination Survey. Hypertension 2006;47:833-9.
 Kakizaki M, Kuriyama S, Nakaya N, Sone T, Nagai M, Sugawara Y, et al. Long sleep duration and cause-specific mortality according to physical function and self-rated health: the Ohsaki Cohort Study. J Sleep Res 2013;22: 209-216.
 Grandner MA, Drummond SPA. Who are the long sleepers? Towards an understanding of the mortality relationship. Sleep Med Rev 2007;11:341-60.
 Patel SR, Malhorta A, Gottlieb DJ, White DP, Hu FB. Correlates of long sleep duration. Sleep 2006;29:881-9.
 Mesas AE, Lopez-Garcia E, Leon-Muñoz LM, Graciani A, Guallar-Castillon P, Rodriguez-Artalejo F The association between habitual sleep duration and sleep quality in older adults according to health status. Age Ageing 2011;40:318-23.
 Van Den Berg JF, Van Rooij FJ, Vos H, Tulen JH, Hofman A, Miedema HM, et al. Disagreement between subjective and actigraphic measures of sleep duration in a population-based study of elderly persons. J Sleep Res 2008;17:295-302.
 Zajacova A, Dowd JB. Reliability of Self-rated Health in US Adults. Am J Epidemiol 2011;174:977-83.
 Salomon JA, Nordhagen S, Oza S, Murray CJ. Are Americans feeling less healthy? The puzzle of trends in self-rated health. Am J Epidemiol 2009;170:343-51.
 Idler EL, Benyamini Y. Self-rated health and mortality: a review of twnty-seven community studies. J Health Soc Behav 1997;38:21-37.
 Schubert CR, Cruickshanks KJ, Dalton DS, Klein BE, Klein R, Nondahl DM. Prevalence of sleep problems and quality of life in an older population. Sleep 2002;25:889-93.
 Lee M, Choh AC, Demerath EW, Knutson KL, Duren DL, Sherwood RJ, et al. Sleep disturbance in relation to health-related quality of life in adults: the Fels longitudinal study. J Nutr Health Aging 2009;13:576-83.
 Newbury JW, Marley JE, Beilby JJ. A randomised controlled trial of the outcome of health assessment of people aged 75 years and over. Med J Aust 2001;175:104-7.
 Burström B, Fredlund P. Self-rated health: is it as good a predictor of subsequent mortality among adults in lower as well as in higher social classes. J Epidemiol Community Health 2001;55:836-40.
 American Academy of Sleep Medicine, International Classification of Sleep Disorders. Diagnostic And Coding Manual, 2nd Ed.. Westchester, Illinois: American Academy of Sleep Medicine; 2005.
 National Sleep Foundation [Internet]. Available from: http://www.sleepfoundation.org/; 2014 February 7.
 Moore PJ, Adler NE, Williams DR, et al. Socioeconomic status and health: the role of sleep. Psychosom Med 2002;64: 337-344.
 Hill TD, Burdette AM, Ellison CG, et al. Religious attendance and the health behaviors of Texas adults. Prev Med 2006;42: 309-312.
 Barton J, Spelten E, Totterdell P, Smith L. Is there and optimum number of night shifts? Relationship between sleep, health and well-being. Work Stress 1995;9:109-23.
 Pilcher JL, Ginter DR, Sadowsky B. Sleep quality versus sleep quantity: relationships between sleep and measures of health, well-being and sleepiness in college students. J Psychosom Res 1997;42:583-96.
March 16 2014.
Accepted em April 24 2014.