Bone Density At Risk With Some Birth Control Pills

Teenagers starting to use oral contraception may be putting their long-term bone health at risk.


A new study was published in The Journal of Clinical Endocrinology and Metabolism by Group Health Research Institute scientists on July 19, 2011. It found that the full impact on bones was not apparent for around two years after starting to use the Pill and the impacts were small and dependent on the woman’s age and the Pill’s hormone dose.

The study focused on Pill use by 14 to 18-year-old teenagers and looked at how bone density might change when a woman stops using the Pill. Delia Scholes, PhD, led the study and said that as hormones are a key component of bone health it made sense to study hormonal contraceptives. These are a major source of external hormones for women and the Pill is the most common birth control method worldwide.

A woman’s risk of fractures later in life is influenced by the bone mass she gains in her teens and her 20s, and this age group has the highest use of oral contraceptives. The study’s researchers measured hip, spine, and whole-body bone densities in 301 teenagers aged 14-18, and in 305 young adult women aged 19-30. They measured the bone densities of 389 participants using oral contraceptives with the two most commonly prescribed estrogen doses in Pills: 20-25 micrograms and 30-35 micrograms. These were compared to 217 similar women who were not using this method of contraception. Bone density measurements were taken at the start of the study, and every 6 months for 2 to 3 years. During that time, 172 oral contraceptive users stopped taking the medication, allowing the researchers to measure bone changes after Pill use was discontinued.

They found that after two years, teens who used the 30-35 microgram Pills showed about 1% less gain in bone density at both the spine and whole body sites than teens who did not use hormonal contraceptives. Any differences in bone density between users and non-users of oral contraceptives were less than 2%, and were seen only after two or more years of use, and only at some measured sites. At 12-24 months after stopping, young adult women who used either Pill dose showed small bone density losses at the spine compared to small gains in women who did not take oral contraceptives.

This may seem like a small loss of bone, but its impact in later life could be considerable. The researchers found that additional studies are needed, including looking at bone changes for a longer time after Pill use is discontinued so they can more accurately evaluate how oral contraceptive use is related to fracture risk.

For any young woman with a family history of osteoporosis, this finding is significant in terms of making a sensible contraceptive choice that will not adversely affect their long-term bone health. Additionally, taking extra precautions to optimise bone strength such as weight bearing exercise and ensuring progesterone levels are adequate would be a sensible plan throughout the teens and twenties.