Changes of sleep or waking habits by age and sex in Japanese

We analyzed the effects of age and sex on habitual sleep/wake rhythm and Morningness-Eveningness scores of 2,252 subjects (6-89 years) randomly selected in Shimonoseki, Japan. Subjects were divided into 21 age groups with a matching number of men and women in each age group. The most common sleep parameter patterns by age showed a v- or inverted v-pattern with a turning point in young adulthood or at the period of puberty. During the period between 6 yr. of age to puberty or young adulthood, the bedtimes on weekdays and weekends and the waking times on weekends were delayed, Morningness-Eveningness scores shifted to the evening type, and sleep length on weekdays decreased. After that period, across groups of increasing age, bedtime and waking time on weekdays and weekends became earlier, sleep length on weekdays and sleep latency increased, Morningness-Eveningness scores shifted to morning type, and the number of awakenings increased. The number of daytime naps increased in the 16-19 yr. group, decreased slightly after that age group, but increased again in older groups. The weekday bedtimes of women above 40 yr. of age was significantly later and their sleep lengths significantly shorter than those of men of the same age. Average sleep latency was longer for women than men. The number of awakenings was larger in women above 50 yr. of age than men of the same age group. The turning point of age, gained from the two linear regressions on data for subjects that have a minimum sum of squared error, was between 16 and 25 yr. of age. Average phase of sleep/wake rhythm shifted backward and sleep length decreased in groups from age 6 to puberty or young adulthood. After early adolescence, the average phase of the sleep/wake rhythm shifted forward, sleep latency became longer, and daytime napping increased. Number of awakenings increased rapidly for women's groups over 40 yr. of age and for men's groups after 50 yr. of age. Sex differences in our research are in apparent conflict with previous data and are discussed from the perspective of women's social and domestic roles in Japan.