National polls reveal that over half of the U.S. population reports having one or more symptom of insomnia (difficulty falling asleep, awake a lot during the night, woke too early and couldn’t get back to sleep, and woke up feeling unrefreshed) at least a few times a week (1
). Researchers estimate that chronic insomnia affects between 9 and 24 percent of the general population (3
). Chronic sleep loss is linked to increased risk of developing chronic conditions such as hypertension, obesity, and cardiovascular disease (8
). Further, sleep deprivation has been linked to cognitive impairment and depression, which have implications for job productivity and social functioning (14
). Thus, the total economic, social, and public health burden of insomnia is large.
The burden of insomnia is disproportionately shouldered by women (6
). A meta-analysis of 31 studies with over 1.2 million participants indicates that women suffer from insomnia more than men by around 40% (OR=1.41 with a 95% confidence interval from 1.28-1.55) (32
There are three common explanations for this gender difference in the prevalence of insomnia: physiological, sociological, and psychiatric illness (33
Physiological explanations use animal models and point to hormonal variation to account for sex differences in terms of sleep initiation, maintenance, and quality (34
). Progesterone, estrogen, and testosterone have all been implicated in explaining differences in men’s and women’s sleep patterns (40
Sociological explanations focus on gender inequality in the balancing of competing obligations between work and family (45
). For example, women typically have a greater share of the household responsibilities, especially related to time consuming activities such as child-rearing, food preparation, and cleaning, which may lead to increased trouble falling or staying asleep (46
). Despite multiple studies of the impact of gender differences in work and family obligations on health (47
), researchers have rarely applied this perspective to explain differences in insomnia or insomnia symptoms (50
). One study conducted in Taiwan found that the social role hypothesis only accounts for a small portion of the gender difference in insomnia (33
Psychiatric explanations focus on the differences in prevalence of mental health disorders between men and women and that the gender disparity varies by type of disorder (51
). In particular, women are more likely to suffer from affective and neurotic disorders such as depression, whereas men are more likely to suffer from personality disorders (52
). Because affective disorders are closely linked to insomnia (13
), differences in type and prevalence of psychiatric illness may be a likely candidate to explain the higher prevalence of insomnia symptoms among women. Yet, few studies have empirically explored this hypothesis (30
). These studies show that adjusting for mental health conditions does not fully account for the gender discrepancy in insomnia, each in their own sample: Hong Kong Chinese adults (30
), adults in Central Pennsylvania (31
), and young adults in Uppsala, Sweden (53
There are several limitations to the studies on the contribution of mental health to the higher prevalence of insomnia among women. First, these studies have relied largely on small, regional samples that lack generalizability. Second, they lack a wide range of sociodemographic, behavioral, and mental health history variables. Third, they do not consider both individual and neighborhood-level factors.
While we know of no prior study of neighborhood effects on insomnia symptoms per se, previous research has found evidence that links neighborhood type with sleep duration (54
). We hypothesize that neighborhood characteristics such as noisiness, high population density, and household crowding may affect insomnia symptoms. These characteristics are typically more prevalent in socio-economically disadvantaged neighborhoods. Since women are more likely than men to live in disadvantaged neighborhoods (see ), a neighborhood effect on insomnia symptoms may help explain the gender disparity in insomnia symptoms. Previous research has already shown that there are gender differences in neighborhood effects on health (55
). Thus it is important to account for the contextual environment captured by neighborhood characteristics when examining gender differences.
Weighted Descriptive Statistics of Insomnia Symptoms and Selected Key Variables
Our study seeks to better understand the role of mental health in contributing to the gender disparity in insomnia by 1) assessing insomnia prevalence in the U.S. using a large nationally-representative sample, 2) systematically exploring the relative contribution of sociodemographic factors, chronic conditions, and mental health history to the gender disparity in insomnia symptoms and 3) using a multi-level perspective by including both individual and neighborhood-level factors as possible contributing factors.