Women who take oral contraceptives can counteract bone loss by increasing calcium in their daily diet

Aug 17 2005

Women who take oral contraceptives can counteract bone loss by making sure they have enough calcium in their daily diet, especially early in life, according to Purdue University research.

Earlier research has indicated that optimizing bone mass in adolescence and young adulthood prevents low bone density and osteoporosis later in life. On the other hand, oral contraceptives appear to decrease bone density.

"It's estimated that eight out of 10 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. "The results of our study suggest that the loss for this group can be prevented by increasing calcium intake."

According to the National Academy of Sciences, the recommended dietary allowance of calcium for women age 19 to 50 is 1,000 milligrams a day. The recommended daily allowance of calcium for adolescents age 9 to 18 is 1,300 milligrams a day.

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.

The study compared 135 oral contraceptive users to non-users between the ages of 18 and 30. Three groups were randomized to receive one of three diets: control (less than 800 mg calcium a day), medium dairy (1,000-1,100 mg calcium a day) and high dairy (1,200-1,300 mg calcium a day).

At the end of the 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 percent 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."

Teegarden's laboratory currently is involved in a number of clinical trials to investigate the effect of calcium consumption on body fat. Her studies have shown that a high consumption of calcium slows weight gain for young women, but her more recent studies show that it may take years to make a noticeable difference.