Why We Sleep: Unlocking the Power of Sleep and Dreams

by Matthew Walker

Even with this strict definition, chronic insomnia is disarmingly common. Approximately one out of every nine people you pass on the street will meet the strict clinical criteria for insomnia, which translates to more than 40 million Americans struggling to make it through their waking days due to wide-eyed nights. While the reasons remain unclear, insomnia is almost twice as common in women than in men, and it is unlikely that a simple unwillingness of men to admit sleep problems explains this very sizable difference between the two sexes. Race and ethnicity also make a significant difference, with African Americans and Hispanic Americans suffering higher rates of insomnia than Caucasian Americans—findings that have important implications for well-recognized health disparities in these communities, such as diabetes, obesity, and cardiovascular disease, which have known links to a lack of sleep.