Objective: To determine whether genetic factors partly explain variation in risk of osteoporotic fracture, the true end point of the osteoporosis problem.
Design: Prospective 25 year follow up of a nationwide cohort of elderly Finnish twins.
Setting: The Finnish twin cohort and the national hospital discharge register, covering the entire 5 million population of Finland.
Subjects: All same sex twin pairs born before 1946. The cohort contained 2308 monozygotic and 5241 dizygotic twin pairs (15 098 people) at the beginning of follow up. Main: outcome measure The number and concordance of osteoporotic fractures in the twin pairs, 1972-96.
Results: 786 cohort members sustained an osteoporotic fracture. In women, the pairwise concordance rate for fracture (that is, the relative number of twin pairs in whom the fracture affected both twins in a pair) was 9.5% (95% confidence interval 5.3% to 15.5%) in monozygotic pairs and 7.9% (5.2% to 11.4%) in dizygotic pairs. In men, the figures were 9.9% (4.4% to 18.5%) and 2.3% (0.6% to 5.7%).
Conclusions: Susceptibility to osteoporotic fractures in elderly Finns is not strongly influenced by genetic factors, especially in elderly women. The traditional strategy for prevention of osteoporotic fractures-that is, increasing peak bone mass and preventing age related bone loss-should be changed to include new elements such as prevention of falls and protection of the critical anatomical sites of the body when a fall occurs.