The study followed 703 Caucasian, African American and Hispanic women using oral contraceptive pills (OCPs), the birth control shot Depo-Provera (depot medroxyprogesterone acetate, or DMPA) or nonhormonal contraceptives. They were divided into age groups—one between 16 and 24, and another between the ages of 25 and 33.

Although women who used nonhormonal contraceptives showed little if any loss, women who took OCPs and DMPA lost 0.4–6.8 percent of bone mineral density. BMD loss appeared to differ most by age.

“DMPA users 16–24 years old lost significantly more bone at the spine (4.2% compared with 3.2%) and femoral neck (6.0% compared with 4.2%) than those 25–33 years old,” authors of the study wrote. “However, OCP users 16–24 years old lost significantly less bone density at the spine (0.4% compared with 0.8%) than women 25–33 years of age.”

Many of the study’s participants chose to discontinue DMPA use. Some switched to nonhormonal contraceptives, and were actually able to regain some bone mineral density—up to 4.9 percent at the spine and 3.2 percent at the neck for nonhormonal contraceptive users. Those who switched to OCPs also regained BMD, but their rates were much lower.

Authors wrote, “Use of very-low-dose OCPs after DMPA discontinuation may slow bone recovery.” Women who switched to OCPs were only able to regain up to 2.3 percent at the spine and 0.7 percent at the neck. According to the study, African American participants recovered bone mineral density in the neck better than Hispanic or white women regardless of which method they chose.

Authors wrote, “Recent prospective studies have demonstrated that once DMPA is discontinued, BMD increases more among prior DMPA users than nonusers, suggesting that DMPA-related bone loss is reversible.”

Although this is very encouraging, authors say more information is needed to fully understand bone mineral density recovery.