Calcium + Protein = Strong Bones

Ever since the 1970s, nutritionists have been arguing over the role of protein in maintaining bone health. Some claim a high-protein diet makes the body excrete more calcium, which in turn could weaken bones. Others assert just the opposite: That dietary protein is essential for maintaining strong bones. Who's right? Recent research strongly suggests that the protein proponents were right all along. The research shows that a diet high in protein not only keeps your bones healthy, it can actually significantly slow down the bone loss that leads to osteoporosis (thin, brittle bones that break easily).

Early Research:


Several studies in the 1970s and 1980s showed that a high-protein diet might negatively impact the amount of calcium excreted from the body, but the results were inconclusive. One study of young men in 1981, for instance, showed that a high-protein diet increased urinary excretion of calcium.1 Another study in 1983, however, showed that a high-protein diet usually did not cause excess calcium excretion—and when it did, the effect was only temporary, at the start of the diet.2 Several additional studies since then showed that a high-protein diet has no long-term effects on calcium excretion.

What all the studies show is that the amount of calcium you excrete depends on more than just how much protein you eat. The amounts of phosphorus and magnesium in your diet, for instance, play a significant role. But even more importantly, there's simply a lot of normal variation in the amount of calcium individuals absorb from their food—some people just absorb more than others, for reasons researchers still don't understand. In fact, your ability to absorb calcium from your food is probably more important to your bone health than the total amount of calcium you take in.3

Despite the contradictory evidence, and even though none of the studies showed any long-term negative effects of temporarily increased calcium excretion, some nutritionists use these older studies and recommend that a high-protein diet is bad for your bone health—even though doctors often recommend protein supplements to help patients with broken bones heal faster.

The Latest Research:


The value of dietary protein for building and maintaining strong bones as you get older has been powerfully shown by several recent research studies. In 1998, a study of a number of young women compared the effects on calcium absorption of a low-protein and a high-protein diet. The result? Calcium absorption from food was much lower on the low-protein diet.4

In 2000, results from a long-term dietary study of 191 Roman Catholic nuns were published. This study showed that the amount of protein in a typical diet had no real effect on calcium absorption from food—but normal individual variation in absorption ability did.5

Results from the long-running Framingham Osteoporosis Study, also published in 2000, showed that eating a diet high in protein has a protective effect on your bones as you age. Among the 615 elderly people in the study, the ones who ate the most protein had the strongest bones, while the ones who ate the least protein had the weakest bones. And over the four-year study period, the people who ate the least protein lost significantly more bone mass than the people who ate the most protein. The connection held up regardless of age, weight, smoking habits, calcium intake and even estrogen use.6

More good news came in March 2002, when an important study showed that the combination of a high protein intake and calcium and vitamin D supplements significantly slows bone loss in older adults. The double-blind study followed nearly 350 sixty-five-year-old men and women over a three-year period. All the participants ate their usual diet, but half were also randomly assigned to take a supplement containing vitamin D and 500 milligrams of calcium, while the others took a dummy pill. Neither the participants nor the researchers knew which group they were in. At the end of three years, the researchers found that among the people taking the calcium and vitamin D supplements, the ones who ate the most protein had the strongest bones and also absorbed the most calcium. Among the people taking the dummy pills, there was no connection between the amount of protein in the diet and the amount of bone loss.7

What do all these studies show? They show that when a high-protein diet is combined with high calcium intake, calcium absorption is increased and bones stay stronger. The amount of calcium needed is not very large. In fact, the study participants with the strongest bones took in an average of 1,300 milligrams of calcium each day—only 100 milligrams a day more than the recommended daily amount for adults over age 50.

Important as protein, calcium, vitamins and minerals are for bone health, diet alone is not enough to slow or prevent osteoporosis. Exercise and other measures are crucial.

Calcium Insurance for Women:
According to National Institutes of Health dietary surveys, 90 percent of American women get no more than 800 milligrams of calcium daily, or several hundred milligrams below the recommended amount of 1,200 milligrams daily. Even worse, among girls and young women, 85 percent take in only between 300 and 800 milligrams of calcium daily—far too little to build and maintain strong bones.8 Because calcium is so important to your bone health, you might want to get some extra bone insurance by taking a supplement. Look for a high-quality brand that includes 500 milligrams of calcium citrate or calcium lactate along with vitamin D in the formulation.

Selected References:

  1. Hegsted, M., Schuette, S.A., Zemel, M.B., et al., "Urinary Calcium and Calcium Balance in Young Men as Affected by Level of Protein and Phosphorus Intake," Journal of Nutrition, 111(3), 1981, pages 553-562.
  2. Spencer, H., Kramer, L., DeBartolo, M., et al., "Further Studies of the Effect of a High Protein Diet as Meat on Calcium Metabolism," American Journal of Clinical Nutrition, 37(6), 1983, pages 924-929.
  3. Burckhardt, P., Heaney, R.P., eds., "Nutritional Aspects of Osteoporosis," Proceedings of the International Symposium on Osteoporosis, Lausanne, Switzerland, May 1991 (New York: Raven Press, 1991), pages 115-123.
  4. Kerstettner, J.E., O'Brien, K.O., Insogna, K.L. "Dietary Protein Affects Intestinal Calcium Absorption," American Journal of Clinical Nutrition, 68(4), 1998, pages 859-865.
  5. Heaney, R.P., "Dietary Protein and Phosphorus Do Not Affect Calcium Absorption," American Journal of Clinical Nutrition, 72(3), 2000, pages 758-761.
  6. Hannan, M.T., Tucker K.L., Dawson-Hughes, B., et al.,"Effect of Dietary Protein on Bone Loss in Elderly Men and Women: The Framingham Osteoporosis Study," Journal of Bone Mineral Research, 15(12), 2000, pages 2504-2512.
  7. Dawson-Hughes, B., Harris, S.S., "Calcium Intake Influences the Association of Protein Intake with Rates of Bone Loss in Elderly Men and Women," American Journal of Clinical Nutrition, 75(4), 2002, pages 773-779.
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