Women taking birth control pills may need to increase calcium intake in order to prevent osteoporosis.

Earlier research has indicated that optimizing bone mass in adolescence and young adulthood prevents low bone density and osteoporosis later in life. Birth control pills appear to undermine that process by decreasing bone density.

"It's estimated that eight out of ten women in the United States use oral contraceptives at some time during the years in which peak bone mass is developing," said Dorothy Teegarden, assistant professor in Purdue's Department of Foods and Nutrition.

Calcium Increase May Reduce Risk

"The results of our study suggest that the loss for this group can be prevented by increasing calcium intake."

Researchers compared the effects of dairy intake on the bone density of oral contraceptive users and non-users between the ages of 18 and 30.

The 135 subjects were divided into a control group (less than 800 mg calcium per day), a medium dairy group (1,000-1,100 mg calcium per day), and a high dairy group (1,200-1,300 mg calcium per day).

At the end of a year, women using oral contraceptives and consuming the medium or high-dairy diet gained significantly more bone mineral density in their hips and spines compared to the low-dairy group.

"These results suggest that many women who are using oral contraceptives in their peak bone-development years could reduce their risk of osteoporosis by approximately 3 to 10 percent over one year by making sure they get enough calcium in their diet, Teegarden said.

"This demonstrates the importance of calcium intake, either by getting enough dairy or with supplements."

Recommended Daily Intake

The daily recommended dietary allowance (RDA) of calcium for adolescents age 9 to 18 is 1,300 milligrams. For women age 19 to 50 the RDA is 1,000 milligrams, according to the National Academy of Sciences.

The 12-month study, funded by the American Dairy Association/National Dairy Council, was published in the July issue of Journal of Clinical Endocrinology and Metabolism.