This study looks at the effects of calcium supplementation on bone density in women in their third decade of life. We placed women aged 19-27 who take in low amounts of calcium in their diets in one of two groups. We will give women in one group a placebo (inactive pill) and women in the other group 1500 milligrams of calcium per day (as calcium carbonate). We will monitor the results by looking at the change in bone mineral density measured at the hip, total body, forearm, and spine. Treatment will last 3 years.

This is a randomized, controlled trial of calcium carbonate supplementation (1500 milligrams per day) in third-decade women with low calcium-to-protein intakes. We accept women aged 19-27 on the basis of good health and the 7-day food diary demonstrating a dietary calcium-to-protein ratio (in milligrams:grams) that does not exceed 13. The outcome variable is the change in BMD at hip, total body, forearm, and spine. Treatment lasts for 3 years. We expect that bone mass will increase in both groups but will increase to a greater extent in the calcium-supplemented group than in the nonsupplemented group.

Inclusion Criteria:

• Women in good health
• Dietary calcium-to-protein ratio (in mg:g, as assessed by 7-day food diary) does not exceed 13

Exclusion Criteria:

• Smoking
• Pregnancy
• Lactation
• Endocrine disease