Optimal age for preventing osteoporosis after menopause depends on effects of stopping treatment.

The aim of this study was to model the effect of short (3 year) treatments for osteoporosis at different times after menopause on the risk of osteoporotic fracture and to assess the impact of strategies to target high-risk individuals. Treatment efficacy for hip, proximal forearm, shoulder, and spine fracture were computed from the relationship between bone mineral density (BMD) and fracture in women from Sweden. Treatment that increased hip bone mineral density by 6% over untreated women saved 126 vertebral, hip, proximal humerus, and forearm fractures per 1000 women at the age of 50 years, provided that the effects of treatment persisted. Targeting women with osteoporosis at this age would save an additional 50% of fractures. With age, the number of fractures saved decreased moderately. At the age of 70 years, 133 fractures would be saved in women with osteoporosis compared to 198 in women with osteoporosis at the age of 50 years. Where the effect of treatment was assumed to wear off over 20 years after stopping treatment, the efficacy of treatment was reduced at all ages, but most markedly at the age of 50 years. Where all women aged 50 years were treated, the number of fractures saved per 1000 women decreased from 127 to 15 and, in the case of targeting women with osteoporosis, decreased from 198 to 27 per 1000 women. By contrast, with a persisting effect of treatment, the number of fractures saved increased markedly with advancing age. If all women were targeted at the age of 50 years, 15 fractures would be saved, whereas this increased to 55 per 1000 women at the age of 70 years. When treatment effects wore off more rapidly with an offset half-time of 2.5 years only 5 fractures were saved per 1000 women at the age of 50 years. This figure rose to 23 per 1000 at the age of 70 years. We conclude that, although uncertainty exists concerning the offset of effect of treatments, treatments should be optimally given to women without prior fractures in later life.