Short Sleep Duration Across Income, Education, and Race/Ethnic Groups: Population Prevalence and Growing Disparities During 34 Years of Follow-Up

Purpose

Little is known about population determinants of short sleep duration. The authors examined associations between short sleep duration and income, education and race/ethnicity, and assessed changes over time in relative disparities.

Methods

Questionnaire data from the Alameda County Health and Ways of Living Study (ACS) was obtained at five time-points (1965, 1974, 1983, 1994, and 1999) for short sleep duration (<7 hours sleep per night). Household income, education level, and race/ethnicity were assessed at baseline (n = 6928). Odds ratios were computed to examine short sleep duration across income, education and race/ethnicity, adjusting for age, sex and time-varying covariates, and to assess changes over time.

Results

Prevalence of short sleep at baseline was 15.2%. The (age-adjusted) odds of short sleep was increased for the lowest household income quintile (odds ratio [OR], 1.62; 95% confidence interval [CI], 1.34–1.94), those with less than high school education (OR, 1.51; 95% CI, 1.30–1.75), and among African Americans (OR, 1.97; 95% CI, 1.68–2.30). Relative disparities increased over time for African-American and Hispanic, compared with white, participants.

Conclusions

Socioeconomic position is a robust determinant of short sleep duration, even after adjusting for health-related characteristics linked to short sleep duration.

Introduction

Short sleep duration was first linked to mortality in the scientific literature more than 40 years ago (1) in community-based data that indicated an increased mortality risk among those with a usual sleep duration of less than 7 hours per night. Only a few studies in subsequent decades followed up with reports of similar findings between short sleep and mortality 2, 3, 4. In the past 5 years, however, evidence from large-scale cohort studies further supports the link between short sleep and mortality 5, 6, 7, 8, in addition to incident diabetes (9), coronary heart disease (10), hypertension (11), obesity and worsening metabolic profiles in the population 12, 13, 14, 15. Parallel evidence from experimental studies has provided insights into the physiologic impact of sleep loss on neuroendocrine and metabolic systems 16, 17, 18, 19. Although the accumulation of epidemiologic and clinical evidence is important for understanding the potential role of short sleep as a population health determinant, little is known about what determines patterns of short sleep duration in the population.

It may be that sleep of sufficient duration for the maintenance of health and well-being has become a luxury in modern society. Average sleep duration among U.S. adults ages 18 to 54 years was 6.9 hours per night according to a nationwide poll conducted in 2004, with 16% typically sleeping 6 hours or less and 40% sleeping 7 hours or less (20). Some have suggested that average sleep duration may have declined in the United States during the 20th century as a by-product of increased late-night diversions, such as internet and television, and longer work schedules characteristic of our modern society 21, 22. As with other luxuries that come at the cost of either money or time, sleep may be a resource whose price is beyond the reach of some segments of the population.

Population subgroups, which have been described as having shorter average sleep durations, include night shift workers, minority race/ethnic groups, those with lower social class ranking, and those with fewer years of formal education 5, 7, 23, 24, 25, 26, 27. However, because investigating socioeconomic disparities in short sleep was not the primary aim of most of these studies, they did not assess the extent to which socioeconomic disparities in short sleep duration reflected the influence of other individual characteristics that could impact sleep acquisition, such as chronic health conditions, depression, obesity, smoking, alcohol consumption and physical activity. Additionally, studying these factors could provide insights into potentially modifiable mediators in the pathway between low socioeconomic position and short sleep duration.

The purpose of this study was to examine the relationship between short sleep duration and three indicators of social and economic position, household income, highest achieved level of education, and race/ethnic background, using follow-up data collected over the course of 34 years from residents of Alameda County, California. We also examined the relative influence of other health-related characteristics on the relationship between short sleep and income, education and race/ethnicity, and additionally, assessed whether disparities in short sleep increased over time.