Dietery Calcium and Osteoporosis
January 1998; Volume 1: 12
Source: awson-Hughes B, et al. Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age or older.
N Engl J Med 997;337:670-676.
Inadequate dietary intake of calcium and vitamin D may contribute to the high prevalence of osteoporosis among older persons.
The authors studied the effects of three years of dietary supplementation with calcium and vitamin D on bone mineral density, biochemical measures of bone metabolism, and the incidence of nonvertebral fracture in 176 men and 213 women age 65 years or older who were living at home. They received either 500 mg of calcium plus 700 IU of Vitamin D3 (cholecalciferol) per day or placebo. Bone mineral density was measured by dual-energy x-ray absorptiometry, blood and urine were analyzed every six months, and cases of nonvertebral fracture were ascertained by means of interviews and verified with use of hospital records.
The mean (± D) changes in bone mineral density in the calcium-vitamin D related groups were as follows: femoral neck, +50 ± 0.80 and -0.70 ± 5.03%, respectively (P = 0.02); spine, +2.12 ± 4.06 and 1.22 ± 4.25% (P = 0.04); and total body, = 0.06 ± 1.83 and -1.09 ± 1.71% (P < 0.01). The difference between the calcium-vitamin D and placebo groups was significant at all skeletal sites after one year, but it was significant only for total body mineral density in the second and third years. Of 37 subjects who had nonvertebral fractures, 26 were in the placebo group and 11 were in the calcium-vitamin D group (P = 0.02).
In men and women 65 years of age or older who are living in the community, dietary supplementation with calcium and vitamin D moderately reduced bone loss measured in the femoral neck, spine, and total body over the three-year study period and reduced the incidence of nonvertebral fractures.
COMMENT
Because low bone mass is a strong predictor of nonvertebral fracture, and because osteoporosis and fracture are common, costly, and preventable, encouraging weight-bearing exercise and adequate calcium intake for postmenopausal women and older men is especially important.
Dawson-Hughes and colleagues at Tufts University found a reduced incidence of nonvertebral fractures in the calcium-vitamin D group in a relatively small number of study subjects. The investigators were unable to separate the effects of calcium and vitamin D on fracture or bone loss.
Weight-bearing exercise may be as important in the prevention of osteoporotic fracture as calcium intake, if not more so. The investigators did not recommend a change in exercise prescription or level for the length of the study period.
Few Americans get adequate calcium in their diet, yet it is easy enough. A cup of calcium-fortified orange juice gives 300 mg; half a cup of some kinds of tofu gives 250 mg; 10 dried figs have 270 mg. Soy milk contains 300 mg per cup, now tastes good, and is lactose-free. Nonfat plain yogurt has 400 mg; cow’s milk has almost 300 mg. Cow’s milk remains the principal source of calcium in the U.S. diet. Nonfat, 2%, and whole (3.3%) milk all have roughly the same amount of calcium and vitamin D.
Oxalates in brassicas like broccoli (70 mg per cup) and dark leafy greens like collards (148 mg) and kale (94 mg) do bind the calcium in these vegetables, but the absorbability of calcium from them is roughly the same as the absorbability from calcium in cow’s milk.
While the best daily dose in this population is debated, the National Academy of Sciences now recommends 1200 mg for women over 50 and men over 65; many experts recommend 1500 mg.
Recommendation
Together with weight-bearing exercise, physicians should recommend calcium and vitamin D supplementation to their elderly patients, except those who have clear contraindications, such as hyperparathyroidism, significant renal or hepatic disease, and dietary calcium of more than 1500 mg daily.
But, as much as possible, patients should get their calcium from food, as above. For those who need supplements, chewable calcium carbonate delivers the most calcium for the lowest price. To maximize absorption, supplements should be taken with meals in divided doses of no more than 500 mg. There is no advantage to "natural" or "oyster shell" tablets.
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