Invited commentary: cross-cultural influences on sleep--broadening the environmental landscape.

Recognition among epidemiologists of the adverse health consequences of sleep habits and sleep disorders has flourished in recent years. Identifying and understanding the cross-sectionally defined environmental factors that are associated with individual differences in habitual sleep duration represents an important line of inquiry. Because of the complexity of sleep as a behavior, traditional measures such as socioeconomic and marital status, health habits, and education may require supplementation with types of data that are both novel and less conventional. Studies across cultures offer one such possibility, although it may be necessary to broaden the view of the environment at both the macro level (e.g., seasonal, geographic, and climatic variation) and the micro level (the bedroom milieu and factors that affect it) in order to fully understand the scope of such influences.