Variation in the efficacy of hormone replacement therapy in the preventionof hip fracture

Use of postmenopausal hormone replacement therapy (HRT) has been associated with a reduced risk of osteoporotic fractures. However, it is uncertain wh ether this risk reduction is modified by other risk factors for hip fractur e. In a population-based case-control study in Sweden, we investigated the association between HRT and hip fracture risk within categories of age, bod y measures and lifestyle factors in postmenopausal women. 50-81 years of ag e. Mailed questionnaires and telephone interviews were used to collect data . Of those eligible, 1328 incident cases with hip fracture (82.5%) and 3312 randomly selected controls (81.6%) answered the questionnaire. Ever use of HRT in women less than 75 years old was associated with an odds ratio (OR) of 0.66 (95% confidence interval: 95% CI 0.50-0.87) for hip fracture compa red with OR 0.40 (95% CI 0.21-0.77) in women 75 years or older. We found a significant interaction between HRT and both weight and physical activity ( p<0.05). The protective effect of HRT was particularly pronounced in lean w omen: compared with never HRT users, ever users weighing under 60 kg had an OR of 0.44 (95% CI 0.30-0.66) whereas women weighing more than 70 kg had a n OR of 0.91 (95% CI 0.53-1.-56). Women with low recent leisure physical ac tivity (less than 1 h/week) similarly benefited more from HRT for hip fract ure prevention than women with a higher degree of recreational physical act ivity, The observed interactions with weight and physical activity suggest that HRT has the best protective effect against hip fracture among high-ris k women.