Age at menopause and its relation to osteoporosis.

As one phase of a comprehensive population study of women, bone density was determined in the third lumbar vertebra by dual photon absorptiometric technique. The method involves the use of two radionuclides, which both emit gamma radiation but with different energies (241Am with 59.6 keV and 137Cs with 662 keV). Women in three age strata were studied: 46, 54 and 62 yr. All women aged 46 were still menstruating, while the age strata 54 and 62 were subdivided into two groups: those who still menstruated or had been postmenopausal for a short time and those who had been postmenopausal for many years. The bone mineral content was higher in premenopausal or recently postmenopausal 54-yr-old women than in women of the same age who had been postmenopausal for a long time (P less than 0.01). A similar trend was found for women aged 62 (P less than 0.10). The differences could not be explained by differences in other factors studied, such as body weight, body height, smoking habits or physical activity. No significant differences were found when women with similar menopausal status in different age groups were compared.