Purpose: Early menopause is widely regarded as a risk factor for osteoporosis. The aim of this study was to determine whether this risk is conferred by a lower bone mass.
Patients and methods: Two hundred thirteen normal postmenopausal women and 55 women with postmenopausal osteoporosis (vertebral fractures) underwent bone mass measurements at the lumbar spine, femoral neck, and midshaft using dual-photon absorptiometry. To examine the effect of early menopause, postmenopausal normal women were stratified according to whether menopause occurred before or after the age of 50 years. Patients with osteoporosis were stratified in the same way.
Results: Patients with osteoporosis had menopause at an earlier age than control subjects, but the difference in bone mass between the patients with osteoporosis and the control subjects could not be attributed to this earlier age at menopause. Furthermore, within the osteoporotic patient group, those with early menopause did not have lower bone mass than those with normal age at menopause. Similarly, within the normal subject group, those with early menopause did not have lower bone mass than those with normal age at menopause.
Conclusion: Patients with osteoporosis have lower bone mass, which is independent of the age at menopause. Although a small effect (less than or equal to 5 percent) of early menopause on bone mass cannot be entirely excluded, these data suggest that the amount of bone lost following menopause is the same irrespective of the age at which menopause occurs. If early menopause is a risk factor for osteoporosis, the risk is not conferred by a bone mass substantially lower than predicted had menopause occurred later, but may be related to the duration of exposure to minimal trauma at low bone mass.