Epidemiology of sleep: Age, gender, and ethnicity

American Journal of Clinical Hypnosis,  Jul 2005  by Feldman, Jeffrey B

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Lichstein, K., Durrence, H., Riedel, B., Taylor, D. and Bush A. (2004) Epidemiology of sleep: Age, gender, and ethnicity. Mahwah, NJ: Lawrence Erlbaum Associates.

This book is a scholarly description by faculty members of the University of Memphis (first four authors) and the University of Tennessee of a study that collected 2 weeks of sleep diaries and daytime functioning questionnaires from 772 randomly selected residents of Memphis, Tennessee and adjoining communities. The sample ranged in age from 20 to 98 years old and was equally divided between men and women. "Ethnic diversity" was achieved in the context of the studied community with about 30% African American representation. The major purpose of the study was to "set a new standard for the epidemiological study of sleep" by generating an archive of normal sleep distributed by age, gender and ethnicity. The authors explained their motivation for the project, stating that while there are numerous studies that examined polysomnography data for normal sleepers and individuals with insomnia, and a large amount of self-report data from people with insomnia, there is little self-reported sleep data for normal sleepers. Furthermore, in contrast to prior studies that employed singlepoint, retrospective survey methods, the authors used 2 weeks of data points per participant, assessing multiple dimensions of sleep and daytime functioning. They also adopted what they viewed as "empirically justifiable, conservative, quantitative criteria for insomnia resulting in reliable prevalence data." Specifically, they defined insomnia as someone complaining of insomnia involving sleep onset latency or wake time after sleep onset of greater than 31 minutes, occurring greater than or equal to 3 nights a week, for 6 months or longer. They further required that an individual's score exceed the lower boundary of impairment on at least one of the following 5 measures of daytime functioning: Epworth Sleepiness Scale, Fatigue Severity Scale, Insomnia Impact Scale, Beck Depression Inventory, or State-Trait Anxiety Inventory. Using this criterion they calculated the overall prevalence of insomnia in their respondents to be 15.9%, which by extrapolating from the U.S. census would give an estimate of 31.4 million people with insomnia in this country.

There were a number of other findings that are both of interest and may be confusing. In reviewing their results the authors separately discussed findings in terms of people with and without insomnia. Among individuals without insomnia, the data from the study refutes the notion that sleep, or at least the subjective experience of sleep, universally declines with advancing age. The authors' findings are consistent with other reports that poor sleep in old age is largely a function of poor health, with the sleep of physically healthy older adults similar to that of younger adults. Among normal sleepers, on three measures there was a statistically significant but small magnitude finding of women sleeping worse than men. However, there were no significant differences overall between the sexes on the majority of measures. In contrast to the above two statements the authors found that insomnia is more common in women and older adults. In other words, while the frequency of insomnia is somewhat greater in women and increases in frequency and severity with advancing age for both sexes, there was not self-report of poorer sleep among those older adults who do not report insomnia. Furthermore, the increasing rate of insomnia did not result in a decrement on any of the six measures of mood and performance used in the study. Counter to expectation there was little relationship between sleep and the studies' measures of daytime functioning for people with or without insomnia. Finally, the prevalence of insomnia was virtually the same for African Americans and Caucasians, with the severity of insomnia somewhat worse for African Americans.

This reviewer has reported the major findings of the book with the assumption that the majority of readers of this journal would have an interest in these findings, but would prefer not to have to read through the 238 pages of the book (including indices, references, and well over 100 tables and figures) to obtain this information. Probably the most positive thing about this book is that one can approach it in as much detail as one chooses. All relevant data is provided for sleep researchers and those interested in the methodological issues in this type of research. Findings include measures of sleep quality, insomnia, and daytime functioning by age, gender and race. Additionally, the authors thoughtfully explain their choice of measures, methods, and the rationale for data analyses. The book is logically well organized by chapters as follows: 1. Goals and distinctive characteristics of this survey, 2. A review of epidemiological studies of insomnia and sleep, 3. Methods of this survey, 4. An archive of normal sleep, 5. An archive of insomnia, 6. An archive of the sleep of African Americans, and 7. Summary of main findings. This enables one to readily focus upon the main findings or a specific area of interest. For instance, if, like this reviewer, you are curious personally and professionally about the frequency of night awakenings by age ranges this is available. Specifically, in the age range of 50-59 the mean number of night awakenings for the "broad normal" sample is 1.3 with a standard deviation of 1.0. It takes a brief amount of reading to understand that this group includes good and poor (subclinical) sleepers, but not individuals who meet criterion for insomnia. Results are also available for a "narrow normal" sample (i.e., individuals with no sleep complaints and who exhibited none of the quantitative aspects of insomnia), and alternately, for those who have insomnia.