15-mcg birth control pills inhibit BMD

Certain birth control pills seem to inhibit growth of bone mineral density (BMD) in adolescent girls, a new study shows.

A poster by Jan Stepan, MD, at the American Society for Bone and Mineral Research meeting in Denver , spelled out the risk. About 90 girls ages 15 to 19 were divided into a control group, a group who took 15 mcg of ethinyl estradiol, and a group who took twice the amount, 30 mcg. Both drug groups also received 60 mcg of gestodene. After nine months, the treatment groups switched dosage strengths for another nine months.

The results of the regular whole-body bone mineral content and lumbar spine BMD tests showed girls on 15 mcg failed to gain or actually lost bone mineral density, down 2%. With 30 mcg, the density increased 1% to 2%. The lower dose of “the pill” wasn’t fully replacing estrogen, the theory goes.

Getting girls to increase bone mineral density now – via weight-bearing and resistance exercises, and calcium and vitamin D via salmon, dairy, and spinach – can be tough. As the saying goes, osteoporosis is a pediatric problem with geriatric manifestations. This adds one more thorny issue to the already tangled thicket of teenage reproductive health.