Bone loss and calcium intake affected by dietary protein.




American Journal of Clinical Nutrition

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Unlike the dead, brittle skeleton hanging in the high school biology lab, bone is a living, metabolically active tissue. Throughout life, bone is constantly rebuilding itself. Bone serves as a storehouse for minerals, chiefly calcium, which can be tapped to meet the body's mineral requirements. Bone is broken down through a process called "resorption," releasing its minerals into the general circulation. New bone is then formed to replace the reabsorbed bone, preventing a net loss of bone. This is called bone "remodeling." As we age, however, bone formation begins to fall behind, causing the gradual bone loss that culminates in osteoporosis.

While a certain amount of bone loss seems inevitable with the passage of time, the process is not entirely beyond our control. Dietary and lifestyle measures can, to some degree, help maintain bone health. Poor nutrition and other health habits such as smoking, alcohol abuse, and physical inactivity contribute to bone loss. Exercise, especially through activities like walking that put pressure on the weight-bearing bones, stimulates bone remodeling. Exposure to sunlight is helpful. Sunlight forms vitamin D in the skin, vitamin D in turn increases calcium absorption.

In a recent examination of bone mineral density (BMD) and calcium and dietary protein intake, 342 healthy men and women ages 65 years and older were recruited. The purpose of this study was to establish if there was an association between calcium and vitamin D supplementation, protein intake, and the effects on BMD. Protein intake was recorded at midpoint during this 3-year placebo-controlled study. Every six months, BMD was measured in all of the participants. The average protein intake was 79.1 grams daily. In the control group the calcium malate supplement along with diet provided an average of 1,246 mg of calcium daily, while the placebo group received 871 mg daily through their diet. The results showed that higher dietary protein was considerably associated to favorable BMD levels through the trial, an association that was not seen in the placebo group. The authors concluded that when supplementing with vitamin D and calcium, increasing protein may have positive effects on BMD in older adults.1


1. Dawson-Hughes B, et al. Calcium intake influences the association of protein intake with rates of bone loss in elderly men and women. American Journal of Clinical Nutrition. Apr 2002; 75: 773-779.