Age of menopause in Japanese women: trends and recent changes.

The age of menopause was investigated in a survey conducted in 1987 in 13,996 Japanese women aged 22-86 years, the findings being as follows: (1) The percentage of post-menopausal women showed a sharp linear increase between the ages of 49 and 53 years, the figure being 42.7% at age 50. The rate of increase was slightly lower after 50 years of age. (2) Among the 6477 post-menopausal women, the age at which the peak number had undergone menopause was 50 years (17.7%), followed by 49, 52 and 48 years. The crude mean age of menopause was 49.33 years in post-menopausal subjects aged over 40. The mean age of menopause in urban and rural women was not significantly different. (3) The crude mean age of menopause, calculated by classifying those aged 50 (born in or before 1937) into groups corresponding to 5-year age intervals, was highest in the 1928-32 birth-year group, followed, in descending order, by the 1923-27, 1918-22, 1917 or earlier and 1933-37 groups in all post-menopausal and in urban subjects, while in rural subjects it was highest in the 1918-22 group. However, overall, the adjusted mean age of menopause was highest (50.2 +/- 3.24 years) in the 1928-32 birth-year group, followed by the 1923-27 and 1933-37 groups.