Protein and Calcium Interplay Important to Bone Health

It’s no secret that the incidence of bone fractures increases among the elderly. Adding to that concern, some scientists theorize that high-protein diets may leach calcium from bone, itself leading to bone loss. Now scientists funded by the Agricultural Research Service have released a three-year study suggesting that bone mineral density (BMD) may actually benefit from high-protein diets--with one caveat. The high-protein diet must also meet the recommended dietary allowance of calcium and vitamin D.

The researchers heading the study are with the Calcium and Bone Metabolism Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston, Mass.

The study’s design, which looked at 342 men and women older than 65, included prescreening the amount of calcium each consumed. Only those who did not normally consume high amounts of calcium were chosen. In addition, the study included only participants whose baseline BMD measurements proved average for those over 65.

The researchers supplemented half the participants with 500 milligrams (mg) of calcium and 700 International Units of vitamin D daily. The other half were given placebos. Halfway through the study, dietary intakes of protein, calcium, vitamin D and other nutrients were assessed using a self-administered, but staff-monitored, food-frequency questionnaire. The results showed the mean protein intake for all participants was 79 grams per day. For the calcium- and vitamin D-supplemented group, the mean daily calcium intake was 1,346 mg per day. For the placebo group, calcium intake was just 871 mg per day--well below the recommended 1,200 mgs daily for those over 50.

The participants were tested every six months--six times total--for BMD. The study, published in April’s "American Journal of Clinical Nutrition," showed that a high-protein diet had favorable effects on bone density in the calcium-supplemented group, but not in the unsupplemented group. This suggests that the calcium worked synergistically with the protein to mitigate bone loss. The researchers agree the report proves more research is needed in this area.

ARS is the U.S. Department of Agriculture’s chief scientific research agency.