Prospective study of dietary protein intake and risk of hip fracture in postmenopausal women

Background: The role of dietary protein intake in osteoporosis remains cont roversial. Protein is an important structural component of bone and protein supplementation improves the medical outcome of hip fracture patients, but it is unknown whether protein intake can reduce the incidence risk of hip fracture. Objective: The relation between intake of protein and other nutrients and s ubsequent incidence of hip fracture was evaluated. Design: Nutrient intake was assessed with a food-frequency questionnaire in a cohort of Iowa women aged 55-69 y at baseline in 1986. Incident hip frac tures were ascertained through follow-up questionnaires mailed to participa nts in 1987 and 1989 and verified by physician reports. Results: Forty-four cases of incident hip fractures were included in the an alyses of 104 338 person-years (the number of subjects studied times the nu mber of years of follow-up) of follow-up data. The risk of hip fracture was not related to intake of calcium or vitamin D, but was negatively associat ed with total protein intake. Animal rather than vegetable sources of prote in appeared to account for this association. In a multivariate model with i nclusion of age, body size, parity, smoking, alcohol intake, estrogen use, and physical activity, the relative risks of hip fracture decreased across increasing quartiles of intake of animal protein as follows: 1.00 (referenc e), 0.59 (95% CI: 0.26, 1.34), 0.63 (0.28, 1.42), and 0.31 (0.10, 0.93); P for trend = 0.037. Conclusion: Intake of dietary protein, especially from animal sources, may be associated with a reduced incidence of hip fractures in postmenopausal w omen.