Dairy & Bone Health; Where Is The Evidence…?

In September of 2000, two researchers compiled a review of the 57 studies on dairy products and bone health, which had been published in the scientific literature since 1985. This review was published in the American Journal of Clinical Nutrition (1). The researchers excluded studies with weak evidence or poor techniques, which eliminated more than half of the studies. From the remaining studies, almost 60% of the studies showed no benefit from dairy and 14% found that dairy products actually weaken bones. This means that almost 3/4 of scientifically sound research did not support the bone health benefits of dairy products and some showed actual harm. Not surprisingly, most of this research was financed by the dairy industry, yet with all their influence on research, they could not make a solid case for dairy benefiting bones.

Randomised controlled studies compare an experimental group with a control group and are considered the most valid form of scientific research. A randomised controlled study, funded by the dairy industry, looked at the benefits of  milk on the health of postmenopausal women (2). At the conclusion of this study, the women in the experimental group, fed three eight-ounce glasses of skim milk daily for a year, were still losing more calcium from their bodies than they were absorbing (they were in negative calcium balance). Even though they consumed more than 1400 mg of calcium daily, they still lost twice as much bone as the women in the control group, who were not getting the supplemental milk. 

Inappropriate concern about calcium intake may divert attention and resources from more important nutritional issues. Calcium isn’t the only nutrient that affects bone health. Studies have shown that potassium and magnesium may be even more critical in preventing bone loss, and that beta-carotene, phosphorus and fibre play important roles as well (4,5). Plants are excellent sources of these nutrients. Milk provides no beta-carotene and no dietary fibre (3). Most important, bone health can be more about what we don’t eat than what we do eat. Certain foods and substances – like animal proteins, cigarettes, soft drinks, caffeine, and salt – all affect our body’s ability to absorb and use calcium vs. the loss of calcium from the body (6,7)

Our intestine will always absorb sufficient calcium to meet our needs from the foods we eat. On a diet low in calcium, the efficiency of mineral absorption increases and the intestine takes in more calcium. On a high-calcium diet, more calcium is left in the intestine to be excreted, unused, in the faeces. The intestine is so “smart” about calcium that it never fails to meet the body’s needs (8).

If calcium is the key and milk is such a great source, why are there still 10 million Americans with osteoporosis? Long-standing recommendations to increase calcium intakes have had little or no effect on the prevalence of osteoporosis or fractures in the United States (9).

The truth is, milk is not the only source of calcium and it is not the best source of calcium either. Let’s consider that the original source of calcium is the ground. Calcium, and other minerals, are dissolved in watery solutions and absorbed by the roots of plants. These minerals are then incorporated in the roots, stems, leaves, flowers, and fruits of the plants. Humans can get plenty of calcium the same way it gets into cow’s milk; from the plant foods we eat.

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References;

1-Weinsier R. Dairy foods and bone health: examination of the evidence. Am J Clin Nutr. 2000 Sep;72(3):681-9.

2-Recker R. The effect of milk supplements on calcium metabolism, bone metabolism and calcium balance. Am J Clin Nutr. 1985 Feb;41(2):254-63.

3-J Pennington. Bowes & Church’s Food Values of Portions Commonly Used. 17th Ed. Lippincott. Philadelphia- New York. 1998

4-Tucker KL. Potassium, magnesium, and fruit and vegetable intakes are associated with greater bone mineral density in elderly men and women. Am J Clin Nutr. 1999 Apr;69(4):727-36.

5-New S. Dietary influences on bone mass and bone metabolism: further evidence of a positive link between fruit and vegetable consumption and bone health. Am J Clin Nutr 71:142-151,2000.

6-Ilich J. Nutrition in bone health revisited: a story beyond calcium. J Am Coll 19:715-37, 2000.

7-Cohen A. Review of risk factors for osteoporosis with particular reference to a possible aetiological role of dietary salt. Food Chem Toxicol. 38:237-53, 2000

8-Spencer H. Influence of dietary calcium intake on Ca(47) absorption in man. Am J Med 46:197-205, 1969.

9-Hegsted D. Fractures, calcium and the modern diet. Am J Clin Nutr 74: 571-3, 2000