Several studies have concluded that a high intake of animal protein can lead to a greater loss of bone mass from the thigh bone (femoral neck) and an increased risk of hip fracture. Other studies have found no such connection. Researchers at Tufts University now report that the effect of protein intake on bone mass is highly dependent on the concurrent intake of calcium and vitamin D. Their study involved 342 healthy men and women aged 65 years or older who participated in a three-year, randomized, placebo-controlled trial of calcium and vitamin D supplementation. The calcium group received 500 mg of calcium citrate maleate and 700 IU (17.5 micrograms) of vitamin D daily in the form of supplements. The average total daily calcium intake in the supplement group was 1346 mg/day as compared to 871 mg/day in the control group. The average total protein intake was 79 grams/day varying between 14 and 20 per cent of total energy intake. Plant protein intake was about 5 per cent of energy. Bone mineral density (BMD) was measured every six months at the femoral neck, spine and total body. At the end of the three-year supplementation period the researchers observed that the BMD for total body and femoral neck had increased significantly amongst those in the calcium/vitamin D supplement group who had the highest intake of protein (greater than 20 per cent of total energy on average). BMD in total body and femoral neck decreased in the placebo group irrespective of protein intake. The researchers conclude that a high protein intake is associated with an increase in BMD provided it is accompanied by supplementation with calcium citrate maleate and vitamin D.
Dawson-Hughes, Bess and Susan S. Harris. Calcium intake influences the association of protein intake with rates of bone loss in elderly men and women. American Journal of Clinical Nutrition, Vol. 75, April 2002, pp. 773-79
Heaney, Robert P. Protein and calcium: antagonists or synergists? American Journal of Clinical Nutrition, Vol. 75, April 2002, pp. 609-10 [editorial]