Sleep epidemiology--a rapidly growing field.

The human body has adapted to daily changes in light such that it anticipates periods of sleep and activity. Deviations from the circadian rhythm come with functional consequences. Thus, 17 h of sustained wakefulness in adults leads to a decrease in performance equivalent to a blood alcohol level of 0.05%; the legal limit for driving in many countries. Rats deprived of sleep die after a month or so, and sleep deprivation is used as a common form of torture. Given the readily observable effects of sleep in everyday life, it is unsurprising that there has been scholarly interest in sleep since the beginning of recorded history. Sleep Epidemiology as a subject in its own right has a recognizable history of just over 30 years, with the first modern epidemiological studies of sleep disturbances appearing around 1980. Nevertheless, a PubMed search on the terms ‘sleep/ insomnia’ and ‘epidemiology’ shows the cumulative number of papers on the subject over the past 10 years is already about 10 000. Although this is less for standard risk factors, such as obesity (more than 60 000) and smoking (50 000) (Figure 1), the annual number of papers on Sleep Epidemiology is rising rapidly (Figure 2). This issue of the IJE includes a review of the first comprehensive textbook of Sleep Epidemiology, and the purpose of our Editorial is to give the reader an idea why the coming years are likely to see an increasing interest in sleep studies.