Study Objective: To determine whether the failure to attain normal bone mass in young adulthood contributes to the later development of osteoporotic fractures.

Design: Case-control study.

Setting: Referral-based bone clinic at a large teaching hospital.

Patients: Sequential sample of 35 asymptomatic relatives, aged 19 to 59 years, of patients with osteoporotic fractures, and 24 patients with osteoporotic fractures.

Measurements and Main Results: Bone mineral density in the spine was measured by quantitative computed tomographic scanning. Bone mineral content in the os calcis was measured in 19 of the relatives of osteoporotic patients by single-photon absorptiometry. The values for bone mineral density in the spine were corrected to age 50 years with the regression equation derived from the normal values in the controls. The values were lower in relatives of osteoporotic patients than in controls. In men, the mean values (± standard deviation [SD]) for relatives were 91 ± 16 mg/cm³, and for controls, 129 ± 21 mg/cm³ (P < 0.001). In women, the mean values for relatives were 96 ± 17 mg/cm³ and for controls, 126 ± 19 mg/cm³ (P < 0.001). In the osteoporotic patients, the corrected mean value for men was 53 ± 12 mg/cm³, and for women, 77 ± 20 mg/cm³. The os calcis values did not correlate with the spine values and were mostly well within the normal range.

Conclusions: Mean bone mass is lower in apparently healthy young and middle-aged adult relatives of osteoporotic patients than in normal persons with no family history of osteoporosis. Our findings suggest that the failure to attain an adequate peak bone mass may play an important role in the later development of osteoporotic fractures. Relatives of osteoporotic patients should be advised to have measurements of bone mass taken. This measurement should be taken at the spine, because peripheral sites do not appear to provide adequate information about early osteoporosis.