The Association Between Protein Intake by Source and Osteoporotic Fracture in Older Men: A Prospective Cohort Study

Dietary protein is a potentially modifiable risk factor for fracture. Our objectives were to assess the association of protein intake with incident fracture among older men and whether these associations varied by protein source or by skeletal site. We studied a longitudinal cohort of 5875 men (mean age 73.6 ± 5.9 years) in the Osteoporotic Fractures in Men (MrOS) study. At baseline, protein intake was assessed as percent of total energy intake (TEI) with mean intake from all sources = 16.1%TEI. Incident clinical fractures were confirmed by physician review of medical records. There were 612 major osteoporotic fractures, 806 low-trauma fractures, 270 hip fractures, 193 spine fractures, and 919 non-hip non-spine fractures during 15 years of follow-up. We used Cox proportional hazards models with age, race, height, clinical site, TEI, physical activity, marital status, osteoporosis, gastrointestinal surgery, smoking, oral corticosteroids use, alcohol consumption, and calcium and vitamin D supplements as covariates to compute hazard ratios (HRs) with 95% confidence intervals (CIs), all expressed per unit (SD = 2.9%TEI) increase. Higher protein intake was associated with a decreased risk of major osteoporotic fracture (HR = 0.92; 95% CI, 0.84 to 1.00) with a similar association found for low-trauma fracture. The association between protein and fracture varied by protein source; eg, increased dairy protein and non-dairy animal protein were associated with a decreased risk of hip fracture (HR = 0.80 [95% CI, 0.65 to 0.98] and HR = 0.84 [95% CI, 0.72 to 0.97], respectively), whereas plant-source protein was not (HR = 0.99 [95% CI, 0.78 to 1.24]). The association between protein and fracture varied by fracture site; total protein was associated with a decreased risk of hip fracture (HR = 0.84 [95% CI, 0.73 to 0.95]), but not clinical spine fracture (HR = 1.06 [95% CI, 0.92 to 1.22]). In conclusion, those with high protein intake (particularly high animal protein intake) as a percentage of TEI have a lower risk of major osteoporotic fracture.