Calcium supplements have become big business in the United States. The sale of calcium supplements increased sevenfold from 1980 to 1985, with +130,000,000 being spent on calcium supplements during 1985. The median daily dietary calcium intake for women in the United States is 574 mg and for men is 826 mg. The average American diet contains 389 mg calcium per 1,000 kcal. The Recommended Dietary Allowance (RDA) of 800 mg calcium may be insufficient to meet the needs of women who are “poor absorbers” of calcium. Research linking calcium intake with bone density is confounded by the type of bone measured, the variation in efficiency of calcium absorption among individuals, and the methodology for measuring calcium intake. Although calcium supplements will retard cortical bone loss in some postmenopausal women and are generally safe, they are not so effective as estrogen.

Walden O
J Am Diet Assoc 1989 Mar;89(3):397-400
PMID: 2646349