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Sleep. Sep 1, 2011; 34(9): 1173–1177.
Published online Sep 1, 2011. doi:  10.5665/SLEEP.1232
PMCID: PMC3157658

Sleep Duration and Self-Rated Health: the National Health Interview Survey 2008

Anoop Shankar, MD, PhD,1 Sabanayagam Charumathi, MD, PhD,1 and Sita Kalidindi, MS1,2

Abstract

Background:

Self-rated health (SRH) has been shown to consistently predict overall mortality and cardiovascular mortality in several population-based studies across the world. Similarly sleep duration have been found to be associated with cardiovascular disease (CVD) and mortality. However, relatively few studies have examined the association between sleep duration and SRH, and the results have not been consistent.

Methods:

We conducted a cross-sectional study of n = 20,663 National Health Interview Survey 2008 participants ≥ 18 years of age (56.2% women). Sleep duration was categorized as ≤ 5 h, 6 h, 7 h, 8 h, and ≥ 9 h. The main outcome interest was fair/poor SRH (n = 3043).

Results:

We found both short and long sleep duration to be independently associated with fair/poor SRH, independent of age, sex, race-ethnicity, smoking, alcohol intake, body mass index, physical activity, depression, diabetes mellitus, hypertension, and CVD. Compared with a sleep duration of 7 h (referent), the multivariate odds ratio (95% confidence interval) of fair/poor SRH was 2.29 (1.86–2.83), 1.68 (1.42–2.00), 1.38 (1.18–1.61), and 1.98 (1.63–2.40) for sleep duration ≤ 5, 6, 8, and ≥ 9 h. This association persisted in subgroup analyses by gender, race-ethnicity, and body mass index categories.

Conclusion:

Compared with sleep duration of 7 h, there was a positive association between both shorter and longer sleep duration and fair/poor self-rated health in a representative sample of US adults.

Citation:

Shankar A; Charumathi S; Kalidindi S. Sleep duration and self-rated health: the National Health Interview Survey 2008. SLEEP 2011;34(9):1173-1177.

Keywords: Sleep, sleep duration, self-rated health, NHIS

INTRODUCTION

According to the recent 2010 National Sleep Foundation poll, many Americans suffer from long-term sleep deprivation. The poll as well as other authors1,2 has revealed that there are racial-ethnic differences in sleep quality and duration among Americans. In recent years, a number of studies have indicated that sleep duration could be an important predictor of an individual's health status. Both short sleep and long sleep durations have been found to be associated with diabetes,3 hypertension,3 and cardiovascular disease (CVD),3,4 and mortality.5

Poor or fair self-rated health (SRH) has been shown to consistently predict overall and cardiovascular mortality in several population-based studies across the world.69 As opposed to more objective measures of health status, SRH provides a convenient and inexpensive method of assessing an individual's health, probably across multiple domains (e.g., psychological, behavioral, social, and environmental) and provides an important and valid indicator of an individual's health status and associated health outcomes.10 Chronic health conditions and mental health problems are strong predictors of SRH,1113 but other health-related factors, including sleep may also be important.

However, relatively few studies have examined the association between sleep duration and SRH, and the results have not been consistent. Segovia et al.14 reported that SRH was worse in members of a community sample in Canada who slept for either more or less than 7–8 h, but they did not adjust for potential confounders or consider short and long sleep separately. Steptoe et al.15 studied a sample of 17, 465 university students aged 17 to 30 years and found that students reporting short sleep duration were more likely to have poorer SRH, while long sleep duration was not found to be associated with SRH. Jean-Louis et al.16 found no evidence of an association between quality of well-being and sleep duration in a study of relatively small sample size (n = 273) among middle-aged residents of California. Finally, despite racial-ethnic differences in sleep duration, no previous study has examined the relation between sleep duration and SRH separately by race-ethnicity. In this context, we examined the association between sleep duration and fair/poor SRH in a large, multiethnic sample of US adults after adjusting for confounding factors such as age, education, body mass index (BMI), and other factors.

METHODS

The data for this study are derived from the 2008 National Health Interview Survey (NHIS). The details of the study design, questionnaire and methods are available online.17 In brief, NHIS is a multi-stage probability sample of the civilian, non-institutionalized population of US adults. Blacks, Hispanics, and Asians were oversampled to provide stable estimates of these groups. Information on household telephone status was obtained for 12,597 households that include one civilian adult or child. The current study is based on the sample adult core component of the NHIS survey, administered by in-person interview to randomly selected civilian adults, aged ≥ 18 years. Of the 21,781 adults interviewed, 21,348 had information on sleep duration. After excluding participants who were pregnant (n = 220), those with missing information on self-rated health (n = 13), and other variables included in the multivariable analysis (n = 452), 20,663 were available for the current analysis.

Outcome of Interest

The main outcome of interest in the current study was self-rated health ascertained by the question, “Would you say your health in general is excellent, very good, good, fair, or poor?” As a categorical outcome for this study, we estimated the probability that a survey participant reported that his or her overall health was either “fair” or “poor.”

Exposure Assessment

Sleep duration was assessed by asking participants the following question: “On average, how many hours of sleep do you get in a 24-hour period?” We categorized the response into 5 groups for the current analysis: ≤ 5 h, 6 h, 7 h, 8 h, and ≥ 9 h.

Information on demographic factors, socioeconomic characteristics, lifestyle characteristics, and health status were obtained through a standardized questionnaire. Age was included as a continuous variable. Education was categorized into less than high school graduate, high school graduate, and more than high school graduate. Cigarette smoking was classified into never smoker, former smoker, and current smoker. Alcohol consumption was categorized into never drinker, former drinker, current light drinker, current moderate drinker, current heavy drinker and based on questionnaire response. BMI was calculated with self-reported height and weight as weight in kilograms divided by height in meters squared. Overweight was defined as BMI 25–29.9 kg/m2 and obese as BMI ≥ 30 kg/m2. No exercise was defined as not engaging in light or moderate leisure-time physical activity for ≥ 10 min/week. Depression was assessed from the question, “How long have you had depression, anxiety, or emotional problem?” with the response categorized into absent, chronic (≥ 3 months), and not chronic (< 3 months).

Statistical Analysis

We compared the characteristics of the study participants by categories of sleep duration employing the χ2 test or analysis of variance, as appropriate. We estimated the odds ratio (OR) and 95% confidence interval (CI) of fair/poor SRH (our primary outcome) associated with various categories of sleep duration employing logistic regression models. In these models, we categorized sleep duration into 5 groups: ≤ 5, 6, 7, 8, ≥ 9 h, and used 7 h of sleep as the referent category. We chose sleep duration of 7 h as the reference category because (1) previous studies (including a study by our group) have shown 7 h sleep duration to be associated with the lowest risk of CVD and mortality4,5,18,19; and 2) the National Institutes of Health (NIH) have recommended 7–8 h of sleep for adults for reducing sleepiness and to avoid increased risks of obesity, diabetes, and CVD.20 We used 2 nested logistic regression models, both with similar sample size. In the first model, we adjusted for age (years) and sex, and in the second multivariable model, we additionally adjusted for race-ethnicity (non-Hispanic white, non-Hispanic blacks, Mexican Americans, others), education (< high school, high school, > high school), smoking categories (never, former, current), alcohol intake (never drinker, former drinker, current light drinker, current moderate drinker, current heavy drinker ), BMI categories (normal, overweight, obese), no exercise (absent/present), depression categories (absent, chronic, not chronic), diabetes (absent/present), hypertension (absent/present), CVD (absent/present). To examine the consistency of the association between sleep duration and fair/poor SRH, we performed stratified analysis by potential confounders such as gender, race-ethnicity, and BMI categories. To examine if the results hold if we dichotomize SRH by different cut-points, we also performed a sensitivity analysis repeating the analysis in Table 2 using excellent/good SRH as the outcome variable. All analyses were weighted to account for the complex survey design and survey non-response using SUDAAN (version 8.0; Research Triangle Institute, Research Triangle Park, NC) and SAS (version 9.2; SAS Institute, Cary, NC) software.

Table 2
Association between sleep duration and fair/poor self-rated health (SRH) in the whole population

RESULTS

Baseline characteristics of the sample are presented in Table 1. Compared to those who slept 7 h/day, those with both shorter and longer durations of sleep were more likely to be: older, women, non-Hispanic blacks; high school or below educated; current smokers; former drinkers; obese; had higher prevalence of chronic depression, diabetes, hypertension, and CVD; and less likely to exercise.

Table 1
Baseline characteristics of the study population by usual sleep duration

Figure 1 shows the distribution of SRH categories by sleep duration. Compared to those who slept 7 h/day, those with both shorter and longer duration of sleep had higher prevalence of fair/poor SRH. In Table 2, taking 7 h of sleep as the referent category, we found that both shorter and longer sleep duration were positively associated with fair/poor SRH in the age, sex-adjusted model as well as the multivariable model. In Table 3, compared to a referent category of 7 h of sleep, the association between shorter and longer sleep duration and fair/poor SRH was consistently present both among men and women. Table 4, the association between sleep duration and fair/poor SRH was present separately among non-Hispanic whites, non-Hispanic blacks, Hispanic Americans, and others. Similarly, in Table 5, the association between sleep duration and fair/poor SRH was present separately in obese and non-obese subjects. When we repeated the analyses in Table 2 using excellent/good SRH as an outcome variable, as expected, the pattern of association was inverse of that using fair/poor SRH as an outcome variable. For example, compared to sleep duration of 7 h, the multivariable OR (95%) of excellent/good SRH was 0.54 (0.46–0.63), 0.72 (0.64–0.80), 0.93 (0.84–1.03), and 0.56 (0.49–0.65) for sleep duration ≤ 5, 6, 8, and ≥ 9 h, respectively.

Table 3
Association between sleep duration and self-rated health (SRH), by gender
Table 4
Association between sleep duration and self-rated health (SRH), by race-ethnicity
Table 5
Association between sleep duration and self-rated health (SRH), by body mass index categories

DISCUSSION

In a large multiethnic sample of US adults, we found that compared to 7 h of daily sleep, those with shorter or longer sleep duration were more likely to report fair/poor SRH. This association was found to be independent of age, sex, race-ethnicity, smoking, alcohol intake, BMI, education, physical activity, depression, diabetes mellitus, hypertension, and CVD. Furthermore, this observed association between sleep duration and fair/poor SRH was consistently present in subgroup analyses by gender, race-ethnicity, and BMI categories.

In the current study, short sleep duration was found to be associated with fair/poor SRH. Both short as well as long sleep duration may contribute to poor SRH by impairing mood and cognitive functioning21,22 or because of an increase in fatigue.23 Short and long sleep duration have been reported to be related to a number of adverse physiological changes, including impaired glucose tolerance,24 inflammation,25 high uric acid levels,26 which increase the risk of chronic diseases such as diabetes, obesity, and hypertension.3 Short and long sleep duration may also be a consequence of poor SRH; individuals with a poorer health status could be more likely to experience disturbed sleep and/or may be less accurate in estimating their sleep duration. In addition, long sleep duration may be a marker of undiagnosed medical conditions that may affect a subject's subjective health rating, such as sleep disordered breathing/sleep apnea,27 low thyroid function,28 or undiagnosed heart failure.29 Given that the present data are cross-sectional, we are unable to determine whether short and long sleep contributes to poor SRH or vice-versa. However, in the context of recent research it is likely that the relationship is bi-directional.

Recent studies have reported that both short sleep and long sleep duration are associated with objective health outcomes, including diabetes mellitus,3 hypertension,3 and CUD,3,4 and mortality.5 In contrast, relatively few studies have examined the association between sleep duration and subjective health outcomes, such as SRH and the results have not been consistent. Segovia et al.14 in a Canadian community-based study reported that sleep duration shorter or longer than 7 to 8 hours was associated with poor SRH, but they did not adjust for potential confounders or consider short and long sleep separately. Steptoe et al.15 studied a sample of 17, 465 university students and found that only short sleep duration was associated with poor SRH. Jean-Louis et al.16 found no evidence of an association between sleep duration and SRH in a small sample size study (n = 273) of middle-aged residents of California. In the current study, we found that compared with 7 hours of sleep, both shorter and longer sleep durations were independently associated with poor SRH. The magnitude of association was strongest for sleep durations ≤ 5 h and ≥ 9 h. In addition, several previous authors1,2 have reported racial-ethnic differences in sleep duration among Americans. In this context, in the current study, in a separate subgroup analysis among different racial-ethnic groups, we found that the association between sleep duration and poor SRH was consistently present among all subgroups.

Advantages of our study include its large, nationally representative sample size, and multiethnic nature. Our study has some limitations. First, since the NHIS survey is cross-sectional in nature, we cannot establish the temporal nature of the association between sleep duration and SRH. Second, sleep duration was measured subjectively, from self-report; a more objective measure such as actigraphy will help in limiting exposure misclassification that may be present in the current study. Third, our choice of sleep duration of 7 hours as the reference category is somewhat arbitrary and mostly based on limited evidence on the association of sleep duration to CVD and mortality. It is possible that the association between sleep duration and SRH is more accurately examined using alternate reference categories.

In summary, in a large representative sample of US adults, we found that compared to 7 h of sleep, those with shorter or longer sleep duration were more likely to report fair/poor SRH. This association was found to be independent of age, sex, race-ethnicity, smoking, alcohol intake, BMI, education, physical activity, and depression. Furthermore, this association between sleep duration and fair/poor SRH was consistently present in all racial and ethnic groups.

DISCLOSURE STATEMENT

This was not an industry supported study. The authors have indicated no financial conflicts of interest.

ACKNOWLEDGMENTS

This study was funded by an American Heart Association national Clinical Research program grant (to Dr. Shankar).

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