Calcium and Protein: Both are Necessary for Bone Health

Source: Tufts University
May 16, 2002 (Reviewed: April 19, 2004)

While some research has indicated that too much protein can adversely affect calcium levels and, therefore, bone mass, Tufts University researchers have recently found that adequate protein intake, in concert with calcium and vitamin D supplementation, may be protective for bones. Their findings are published in the American Journal of Clinical Nutrition.

Effect of nutrients on bone density

The study was a 3-year, randomized, placebo-controlled trial including 342 healthy men and women aged 65 and older. The participants received either daily supplements of calcium (500 mg) and vitamin D (700 IU), or placebo. Baseline bone mineral density (BMD) was measured in the hip, spine, and total body using a dual-energy X-ray absorptiometer (DEXA).

Dietary intakes of protein, calcium, vitamin D, total energy, and other nutrients were assessed using a food frequency questionnaire at the 18-month point. Fractional calcium absorption, serum parathyroid hormone, and other biochemical measurements were also recorded.

Changes in bone mineral density

After 3 years, total body DEXA measurements revealed significantly less BMD loss in supplement users in the highest tertile of protein intake (18-30% calories from protein) compared with supplement users in the lowest tertile (10-15% calories from protein) (p=0.046). Protein intake was not significantly associated with changes in BMD in the placebo group. The interaction between the supplements and protein intake was significant for total body BMD (p=0.044), but not for BMD measurements of the hip and spine (although BMD changes in the hip followed a pattern similar to that of the total body).

Protein and calcium absorption

The relationship between protein intake and supplement use also seemed to influence the absorption of calcium. In the placebo group, less calcium was absorbed as the amount of protein consumed increased (p=0.017). Calcium absorption rates of supplement users were higher overall than those of placebo users -- probably due to higher intakes of calcium -- but they were not altered by protein intake (p<0.001). Another finding of note was that the protein source -- plant or animal -- did not appear to affect BMD-related changes.

What the results mean

These findings add to the understanding of the relationship between bone health and protein, calcium, and vitamin D, all of which, it appears, are necessary for strong bones. According to this study, calcium alone is not enough to protect bone mass if protein intake is low. And while too much protein may decrease calcium absorption, this effect seems to be negated if enough calcium is consumed.

Advice for patients

The bottom line for patients is that they need to get enough of all the nutrients important for bone health. The amount of protein currently recommended for healthy adults is 0.8 g per kg body weight. There is some debate as to whether this is enough for some elderly populations, but in the current study even those volunteers in the lowest tertile of protein intake were consuming about 1.0 g/kg/day.

However, calcium intakes were not as encouraging. The volunteers who didn't receive the calcium supplement were well below the recommended intake of 1,200 mg daily. And many older adults don't get enough vitamin D (400 IU for people aged 51-70 and 600 IU for people over 70). Therefore, supplements of calcium and vitamin D may be indicated for some patients.

Source

• Calcium intake influences the association of protein intake with rates of bone loss in elderly men and women. B. Dawson-Hughes, S. Harris, Am J Clin Nutr, 2002, vol. 75, pp. 773--779

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