Protein intake: effects on bone mineral density and the rate of bone loss in elderly women

Background: The role of dietary protein in bone metabolism is controversial. Objective: We investigated the associations of dietary protein intake with baseline bone mineral density (BMD) and the rate of bone loss over 3 y in postmenopausal elderly women. Design: Women aged 65-77 y (n = 489) were enrolled in an osteoporosis intervention trial. We studied the associations of protein intake as a percentage of energy with baseline BMD and the rate of bone loss in 96 women in the placebo group (n = 96). We also examined the effect of the interaction of dietary calcium intake with protein intake on BMD. Results: In the cross-sectional study, a higher intake of protein was associated with higher BMD. BMD was significantly higher (P < 0.05) in the spine (7%), midradius (6%), and total body (5%) in subjects in the highest quartile of protein intake than in those in the lower 2 quartiles. This positive association was seen in women with calcium intakes >408 mg/d. There was no significant effect of protein intake on hip BMD. In the longitudinal study of the placebo group, there was no association between protein intake and the rate of bone loss. Conclusions: The highest quartile of protein intake ((x) over bar: 72 g/d) was associated with higher BMD in elderly women at baseline only when the calcium intake exceeded 408 mg/d. In the longitudinal study, no association was seen between protein intake and the rate of bone loss, perhaps because the sample size was too small or the follow-up period of 3 y was not long enough to detect changes.