Effect of dietary protein on bone loss in elderly men and women: The Framingham Osteoporosis Study

Few studies have evaluated protein intake and bone loss in elders. Excess p rotein may be associated with negative calcium balance, whereas low protein intake has been associated with fracture. We examined the relation between baseline dietary protein and subsequent 4-year change in bone mineral dens ity (BMD) for 391 women and 224 men from the population-based Framingham Os teoporosis Study. BMD (g/cm(2)) was assessed in 1988-1989 and in 1992-1993 at the femur, spine, and radius. Usual dietary protein intake was determine d using a semiquantitative food frequency questionnaire (FFQ) and expressed as percent of energy from protein intake. BMD loss over 4 years was regres sed on percent protein intake, simultaneously adjusting for other baseline factors: age, weight, height, weight change, total energy intake, smoking, alcohol intake, caffeine, physical activity, calcium intake, and, for women , current estrogen use. Effects of animal protein on bone loss also were ex amined. Mean age at baseline (+/-SD) of 615 participants was 75 years (+/-4 .4; range, 68-91 years). Mean protein intake was 68 g/day (+/-24.0; range, 14-175 g/day), and mean percent of energy from protein was 16% (+/-3.4; ran ge, 7-30%), Proportional protein intakes were similar for men and women. Lo wer protein intake was significantly related to bone loss at femoral and sp ine sites (p less than or equal to 0.04) with effects similar to 10 lb of w eight. Persons in the lowest quartile of protein intake showed the greatest bone loss. Similar to the overall protein effect, lower percent animal pro tein also was significantly related to bone loss at femoral and spine BMD s ites (all p < 0.01) but not the radial shaft (p = 0.23), Even after control ling for known confounders including weight loss, women and men with relati vely lower protein intake had increased bone Loss, suggesting that protein intake is important in maintaining bone or minimizing bone loss in elderly persons, Further, higher intake of animal protein does not appear to affect the skeleton adversely in this elderly population.