Objectives: To study the fracture reducing potential of hormone replacement therapy (HRT) at a population level, the effect of age on the fracture reducing potential of HRT, and to examine whether socio-economic factors confound the effects of HRT on fracture risk.
Subjects and methods: Case-control study. All women who sustained any fracture during the year 2000 in Denmark served as cases (n=64,548). For each case, three age-matched controls were randomly drawn from the background population (n=193,641). The main exposure was the average daily dose of HRT (expressed as defined daily doses DDD/day). Adjustments were made for co-morbidity, socio-economic factors, and prior fracture.
Results: A fracture risk reduction was seen in women aged>or=50 years using >or=0.3 DDD/day. The risk reduction for any fracture was larger in women aged>or=60 years (0.3-0.99 DDD/day: odds ratio (OR)=0.77, 95% confidence intervals (CI): 0.73-0.82, >or=1 DDD/day: OR=0.61, 95% CI: 0.56-0.67) than in women aged 50-59 years (0.3-0.99 DDD/day: OR=0.92, 95% CI: 0.85-0.99, >or=1 DDD/day: OR=0.77, 95% CI: 0.70-0.84). Larger risk reductions were seen for Colles' fractures (age 50-59 years: OR=0.64 for 0.3-0.99 DDD/day, and OR=0.57 for >or=1 DDD/day, age>or=60 years: OR=0.52 for 0.3-0.99 DDD/day, and OR=0.40 for >or=1 DDD/day). Adjustment only changed the estimates little. No difference between oral and dermal preparations could be found.
Conclusions: Hormonal replacement therapy possesses a fracture-reducing potential at population level even at dosages lower than usually recommended. The risk reduction was larger with advancing age for any fracture and Colles' fractures.