Risk factors for hip fracture and a possible effect modification by hormone replacement therapy. The Danish nurse cohort study.

Objective: To identify risk factors for hip fracture and to examine whether hormone replacement therapy (HRT) modifies the effect of these risk factors.

Design: Prospective cohort study.

Setting: The Danish Nurse Cohort Study.

Participants: 14,015 female nurses aged 50 years and above who in 1993 completed a questionnaire on general health and lifestyle issues, reproductive history including information on HRT, and family history of osteoporosis and personal history of a wrist fracture.

Outcome Measures: End-point was the first-ever hip fracture registered in the Danish National Hospital Register during the period from 1993 to 1999.

Results: During the follow-up period 245 hip fractures were identified. Ever users of HRT had a lower risk of hip fracture (hazard ratio 0.69; 0.50-0.94). Women reporting a poor health (hazard ratio 2.01; 1.30-3.11), restrictions in daily activities (hazard ratio 1.52; 1.05-2.21), low body mass index (hazard ratio 1.65; 0.98-2.77), and leisure time sedentary physical activity (hazard ratio 1.88; 1.30-2.70) were main identified risk factors for hip fracture. HRT did not modify the effect of risk factors on the risk of hip fracture.

Conclusion: This study confirms that women with a frail health are at increased hip fracture risk and that ever use of HRT decreases the risk of hip fracture. HRT did not modify the effect of these risk factors, indicating that the preventive effect of this therapy is independent of risk factors.