Insomnia

Insomnia is the most common sleep disorder and is among the most prevalent of all mental health disorders. Evaluating the epidemiology of insomnia is challenging because insomnia is an umbrella term used to describe a wide range of sleep behavior—from a single, acute complaint to chronic, clinically significant insomnia—that not surprisingly results in a wide range of prevalence estimates. Interpretation of any given prevalence rate requires understanding how insomnia is defined and assessed. A robust literature supports insomnia as a risk factor for many psychiatric disorders, whereas a smaller but growing literature indicates it is also a risk factor for many medical disorders. The reverse is also true with many psychiatric and medical disorders predicting insomnia risk. Evidence of minimal racial/ethnic differences may underestimate clinically significant insomnia in non-White groups. The mechanisms, causal paths, and mediators/moderators of these risk relationships are not currently well understood. Age, sex, socioeconomic status, and genetics are static risk factors that may moderate other insomnia risk relationships, including racial/ethnic differences. Hyperarousal, a component of most, if not all, insomnia models is a traditional insomnia risk factor. However, limited, largely cross-sectional support combined with emerging support for hyperarousal-related factors raises questions regarding hyperarousal’s role as a risk factor. This chapter reviews the current literature on the epidemiology of insomnia and risk factors of insomnia, describes its weaknesses, and suggests areas for research prioritization and methodological improvement.