Protein intake and risk of hip fractures in postmenopausal women and men age 50 and older

In this study, we followed postmenopausal women and men aged 50 and above for up to 32 years and found no evidence that higher protein intake increased the risk of hip fracture. Protein intake from specific sources was inversely associated with risk, but these associations appeared to differ by gender. We examined the association between intakes of total and specific sources of protein and hip fracture risk in postmenopausal women and men over 50 years of age. Our hypothesis was that a higher protein intake would not be associated with a higher risk of hip fractures. In this analysis, we followed 74,443 women in the Nurses' Health Study between 1980 and 2012 and 35,439 men from the Health Professionals Follow-up Study between 1986 and 2012. Health and lifestyle information and hip fractures were self-reported on biennial questionnaires. Protein was assessed approximately every 4 years with a food frequency questionnaire. Relative risks (RR) were computed for hip fracture by quintiles of total, animal, dairy, and plant protein intakes using Cox proportional hazard models, adjusting for potential confounders. During follow-up, we ascertained 2156 incident hip fractures in women and 595 fractures in men. Among men, we observed significant inverse associations for each 10 g increase of total protein (RR = 0.92, 95% CI = 0.85-0.99) and animal protein (RR = 0.91, 95% CI = 0.85-0.98) intakes. Total and animal proteins were not significantly associated with hip fractures in women. Both plant (RR = 0.88, 95% CI 0.79-0.99 per 10 g) and dairy protein (RR = 0.92, 95% CI 0.86-0.97) were associated with significantly lower risks of hip fracture when results for men and women were combined. None of these associations were modified by BMI, smoking, physical activity, age, or calcium intake. We found no evidence that higher protein intake increases risk of hip fracture in these Caucasian men and women. Protein intake from specific sources was inversely associated with risk, but these associations appeared to differ by gender.