Women who are taking birth control pills have lower bone mineral density (BMD) than women who have never used oral contraceptives.

Past studies in postmenopausal women have found that supplementation with the hormones estrogen and progestin actually helps maintain bone density. But few have looked at the effect of hormones on premenopausal women.

After adjusting for age, body mass index and height, BMD in oral contraceptive users was 2.3% to 3.7% lower than in women who had never used oral contraceptives, especially in the spine and the upper part of the thigh bone.

Canadian Medical Association Journal October 16, 2001;165:1023-1029