Protein,
Calcium and Bone Density, Part 1
G.
Douglas Andersen, DC, DACBSP, CCN
Volume
20, number 21, 10/7/02, page 15
Is protein good or bad for bone density?
Among the health concerns facing the United States are an aging population,
skyrocketing rates of obesity and rapidly increasing levels of bone disease.
To fight the battle of the bulge, many are turning to diets that emphasize
protein. High-protein diets have caused concern for some public health
officials because the rate of fractures in people over 65 is epidemic,
as are the numbers of seniors with osteopenia and osteoporosis.
By volume, bone is 50 percent mineral, 64 percent of which is calcium.
Protein makes up most of the remaining 50 percent. A large percentage
of the amino acids in bone collagen is trapped and unable to be used for
new protein synthesis. Therefore, proper osseous turnover requires regular
ingestion of adequate amounts of dietary protein.1
It has been known for many years that dietary protein increases urinary
calcium losses.2 Dr. Stephanie Atkinson, a calcium expert from McMaster
University in Canada, states that for each gram of protein consumed, we
excrete 1-1.5 mg of calcium in our urine. If a woman eats 70 grams of
protein per day, her urinary calcium losses will range from 70 to 105
mg of calcium. This may seem like an insignificant amount, given that
the RDA for calcium is 1,200 mg for women over 50.
However, the average American only consumes 600 mg of calcium per day.3
Subtract 100 mg from the average diet, and it is clear that protein
can have a significant effect on bone health. In a recent paper, researchers
found that high protein intakes were associated with an increased risk
of fracture, but only if dietary calcium intakes were low (less than 400
mg per day).4
Conflicting Studies
Studies have shown that premenopausal and postmenopausal women with high
total protein intakes and high animal-to-vegetable-protein ratios have
a higher incidence of fractures.5,6 In contrast,
other studies have conflicted with these findings and have shown that
higher dietary protein intakes are associated with reduced fracture risk
in postmenopausal women.7 In one study of geriatric
patients recovering from hip fractures, the group given 20 grams of protein
supplements per day for one year, along with calcium and vitamin D, showed
greater improvement in bone mineral density than the calcium and vitamin
D group that received no extra protein.8
Part II will expand on this topic and take an in-depth look at a large,
three-year, randomized controlled trial on calcium, vitamin D, and how
protein affected the bone density of over 300 healthy men and women 65
years of age and older.
References
1. Heaney RT. Protein and calcium: antagonists or synergists? Am J Clin
Nutr 2002;75:609-10.
2. Heaney RP, Recker RR. Effects of nitrogen, phosphorus, and caffeine
on calcium balance in women. J Lab Clin Med 1982;99:46-55.
3. Liebman B. Bare bones. Nutrition Action Health Letter 2002;29:1-8.
4. Meyer HE, Pedersen JI, et al. Dietary factors and the incidents of
hip fracture in middle-aged Norwegians. Am J Epidemiol 1997;145:117-23.
5. Sellmeyer DE, Stone KL, et al. A high ratio of dietary animal-to-vegetable-protein
increases the rate of bone loss and risk of fracture in postmenopausal
women. Am J Clin Nutr 2001;73:118-22.
6. Feskanich D, Willet WC, et al. Protein consumption and bone fractures
in women. Am J Epidemiol 1996;143:472-9.
7. Munger RG, Cerhan JR, Chiu BC. Prospective study of dietary protein
and risk of hip fracture in postmenopausal women. Am J Clin Nutr 1999;59:147-5q.
8. Schurch MA, Rizzoli R, et al. Protein supplements increase serum insulin-like
growth factor-1 levels and attenuate proximal femur bone loss in patients
with recent hip fracture. Ann Intern Med 1998;128:801-9.
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