The Pill and bone health: What is the impact?

Combined oral contraceptives (OCs) help decrease a woman’s risk for epithelial ovarian cancer and endometrial cancer, reduce her risk of pelvic inflammatory disease and ectopic pregnancy, and lessen menstrual cramps and pain. But what is their impact on bone mineral density (BMD)?

Several studies have suggested that OC use may stabilize or even increase bone density.1 A new analysis indicates that exposure to the estrogen from OCs during the premenopausal years may have a small beneficial effect on the skeleton in white women.2

The new information is consistent with clinicians’ evolving perspective on combination OC use and bone health, states Andrew Kaunitz, MD, professor and assistant chair in the obstetrics and gynecology department at the University of Florida Health Science Center/Jacksonville.

"In estrogen-replete, healthy ovulatory women, use of combination OC has minimal, but if anything, positive, impact on bone mineral density," observes Kaunitz. "However, we know from other data that in hypoestrogenemic premenopausal women, e.g., perimenopausal women, use of OC has a positive impact on BMD and prevents future osteoporotic fractures."3,4

Review the analysis

To examine the OC-BMD link, researchers in the current analysis looked at 216 white and 260 black women enrolled in the Coronary Artery Risk Development in Young Adults study, a long-term examination of the evolution of cardiovascular disease risk factors in young adults.

In the current analysis, researchers looked at 216 white and 260 black women ages 25-37 who had bone mineral densities measurements taken at the spine, hip, and whole body by dual-energy X-ray absorptiometry. Three years later, whole-body BMD was measured again in 369 of the women. Researchers also checked the women’s oral contraceptive history, including length of use and estrogen dose.

In their analysis, researchers found that cumulative estrogen from oral contraceptives explained 4% of the variation in spine BMD among white women, but it did not explain any of the variance in BMD among black women. Cumulative oral contraceptive estrogen dose was associated with a decreased risk for low bone density (lowest quartile) at the spine, hip, and whole body in white women. When women in the highest quartile of cumulative oral contraceptive estrogen exposure were compared with those in the lowest quartile, the odds ratios were 0.08 at the spine, 0.23 at the hip, and 0.37 at the whole body. There was no relation between oral contraceptive use and low bone density among black women, and oral contraceptive use did not predict longitudinal changes in whole body bone mineral density among white or black women.

A valuable contribution of the study is recognition of the importance of OC use duration as a determinant of bone health, says Kaunitz.

More research planned

The impact of the Pill on bone mineral density is a topic of interest for Kristin Cobb, PhD, a lecturer in the department of health research and policy at Stanford University in Palo Alto and lead author of the analysis.

Cobb is involved in an ongoing examination of the effect of oral contraceptives on BMD in female distance runners, who have low bone density because they do not menstruate, part of what is defined as the female athlete triad.

First described at a meeting of the American College of Sports Medicine in 1992, the triad consists of disordered eating, menstrual irregularities, and osteoporosis.5 Although the triad can occur in any athlete, certain groups, such as distance runners and swimmers, are at particularly high risk due to the significant energy deficits that go along with their activities.6

The randomized trial is assigning women runners to two groups, those who use OCs and those who do not, and following them for two years, says Cobb.

"It’s tricky to recruit for this because we wanted fairly young women runners who were at the age where it could influence their bone density to a certain extent," she states. "We hope to have some interesting results from it, because I think this will be the first randomized trial with a large enough number to look at oral contraceptive use as a possible treatment for bone density loss in women runners."

References

1. Blackburn RD, Cunkelman JA, Zlidar VM. Oral Contraceptives — An Update. Population Reports, Series A, No. 9. Baltimore: Johns Hopkins University School of Public Health, Population Information Program; Spring 2000.

2. Cobb KL, Kelsey JL, Sidney S, et al. Oral contraceptives and bone mineral density in white and black women in CARDIA. Osteoporos Int 2002; 13:893-900.

3. Michaelsson K, Baron JA, Farahmand BY, et al. Oral-contraceptive use and risk of hip fracture: A case-control study. Lancet 1999; 353:1,481-1,484.

4. Gambacciani M, Spinetti A, Taponeco F, et al. Longitudinal evaluation of perimenopausal vertebral bone loss: Effects of a low-dose oral contraceptive preparation on bone mineral density and metabolism. Obstet Gynecol 1994; 83:392-396.

5. Yeager KK, Agostini R, Nattiv A, et al. The female athlete triad: Disordered eating, amenorrhea, osteoporosis. Med Sci Sports Exerc 1993; 25:775-777.

6. Furia J. The female athlete triad. MedGenMed 1999; 1(1) [formerly published in Medscape Orthopaedics & Sports Medicine eJournal 1999; 3(1)]. Web: www.medscape.com/viewarticle/408496.