Bone Density Reduction Observed in Some Birth Control Pill Users

A recent study conducted by scientists from the Group Health Research Institute (GHRI) showed that birth control pills have the potential to reduce a woman's bone density. Impact on bone density was dependent on the woman’s age, as well as the pill’s hormone dose.

The study was led by GHRI Senior Investigator Delia Scholes, PhD.

According to Scholes, hormones are an important component of bone health, and hormonal contraceptives are a major source of external hormones for women; a woman's risk of fractures in her elder years is affected by the bone mass she gains in her teens through her twenties. This age group, stated Scholes, has the highest rate of using birth control pills as a form of contraceptive.

"The teen years are when women most actively gain bone, so we thought it was important to look at that age group," stated Scholes. "We found that oral contraceptive use had a small negative impact on bone gain at these ages, but took time to appear, and depended on hormone dose."

Scholes and her fellow researchers studied 301 teenage women between the ages of fourteen and eighteen, and 305 adult women between the ages of nineteen and thirty. They measured the hip, spine, and whole-body bone densities in their participants at the start of the study, and every subsequent six month period for two to three years.

The researchers also focused on the two most frequently prescribed estrogen doses in the pills (20-25 micrograms and 30-35 micrograms).

The bone densities of 389 participants who were taking birth control pills were then compared to the 217 women who were not using birth control pills. Over the duration of the study, 172 birth control pill users stopped taking the pill, and the researchers measured the changes in their bone densities following the discontinuation of the medication.

The researchers found that a teenage woman who used a pill with a dosage of 30-35 micrograms of estrogen for over two years exhibited roughly 1% less gain in bone density at both the spine and whole body sites than teenagers that did not use oral contraceptives.

At twelve to twenty four months after ceasing use of oral contraceptives, teens who had taken 30-35 microgram pills still gained less bone density in the spine than female teenagers that did not use the pill.

Comparatively, the researchers discovered that young adult women, both users and non-users of the pill, exhibited no differences in bone density.

At twelve to twenty-four months after stopping, young adult women who had taken either commonly used pill dose exhibited small bone density losses at the spine in comparison to the small gains in women who did not take oral contraceptives.

Dissimilarity observed in bone density between users and nonusers of the pill were less than 2%; they also were only observed following two or more years of oral contraceptive use.

Scholes stated that further studies which include focusing on bone changes for a longer period of time following the discontinuation of the pill may yield more information concerning how oral contraceptive use is related to fracture risk.

Until then, however, Scholes hopes that these results may help women make informed decisions.

"Bone health, especially for long-term users of the pill, may be one of many factors women consider in choosing a contraceptive method that's right for them," she reported.

It is recommended by the US Surgeon General that females, both users and non-users of oral contraceptives, keep healthy bone density by consuming foods high in calcium and vitamin D, as well as performing weight-bearing exercises and not smoking.

This study was published online on July 13 in The Journal of Clinical Endocrinology and Metabolism.