A new study suggests that women using injectable birth control are at a higher risk of suffering bone mineral density (BMD) loss, a major cause for fractures and disability.

In an effort to determine whether use of depot medroxyprogesterone acetate (DMPA), injectable birth control, is associated with bone density deficit, American researchers followed 95 users of the "birth control shot" for two years.

During that period, 45 women had at least 5 percent bone mineral density loss in the lower back or hip, while 50 women exhibited less than 5 percent bone loss at the same places.

Senior author of the study Abbey Berenson, MD, Department of Obstetrics And Gynecology, University of Texas Medical Branch, Galveston, Texas stated, "Based on these findings, clinicians have the information they need to recommend basic behavior changes for high risk women to minimize BMD loss."

Risk of bone loss higher in some cases:
The researchers noted that women who smoked, those who had never given birth, and whose dietary intake of calcium was lower than the recommended dosage of 600 mg were at a greater risk of bone loss by taking the injection for birth control.

In addition, they found that BMD was more pronounced in women with all the above three factors.

They also observed that factors like age, race or ethnicity, previous contraceptive use, and body mass index [a number, derived by using height and weight measurements, that gives a general indication of whether or not weight falls within a healthy range.] was not related to higher BMD loss.

"Bone mineral density loss is not a significant concern for all women who choose DMPA," said Berenson.

The investigators then tracked 27 women for another year. They found that all those who experienced significant bone density deficit in the first two years continued to lose bone mass, especially at the hip and lower spine.

"These losses, especially among women using DMPA for many years, are likely to take an extended period of time to reverse," said first author Mahburbur Rahman, Center for Interdisciplinary Research in Women's Health, Galveston, Texas.

DMPA a popular form of contraception:
DMPA is a carefree and relatively inexpensive form of contraceptive used by over two million women and teenagers.

The birth control shots are administered once every three months, and because of its high success rate in preventing pregnancy, this long-acting contraceptive is a popular option as opposed to other forms of birth control.

The researchers advise that women using DMPA should consult their physicians about reducing the risk factors for bone deficit. In addition, they propose that they should increase their calcium intake and stop smoking.

The study is published in the journal Obstetrics and Gynecology.