Age and gender difference in habitual sleep-wake rhythm.

We analysed the effects of age and gender on the habitual sleep-wake rhythm in 2252 randomly selected subjects living in Shimonoseki, Japan. Subjects were divided into 21 age groups with a matching number of males and females for each. During the period from primary school to adolescence, the bedtime became delayed and sleep length decreased with age. After that period, with increasing age, bedtime became earlier and sleep length increased. The number of awakenings and the length of daytime naps increased markedly with epoch after 50 years and 70 years of age, respectively. Gender differences were considered to be due to the women's social and domestic customs in Japan.