by Drs. Jerilynn C. Prior & Azita Goshtasebi
Use of “The Pill” prevents bone growth in teenaged women. New evidence resulting from combining two-year-long studies in almost 900 adolescent women using Combined Hormonal Contraceptives (CHC) women, showed negative bone changes.
“The Pill” has been approved and prescribed for over 50 years. It provides high doses of estrogen; estrogen is good for women’s bones, so how could CHC be harmful for teen bones? There are many questions but, first, what’s the evidence?
What’s the evidence that CHC have negative effects on bone in adolescent women?
CeMCOR recently published a meta-analysis of five studies in adolescent women showing negative bone change over two years in those teens using CHC compared with those with natural menstrual cycles1. Meta-analysis is a standardized way of combining research results from many studies; it provides some of our strongest scientific evidence. You can read our meta-analysis here*.
In 885 young women, ages 12-19 years, from China, Brazil, the USA, and Canada, we found that teens taking CHC (n = 558) gained significantly less spinal bone (-0.02 g/cm2) than the young women (n = 327) who were not taking it1. To help you understand these results, we need to explain how bone normally changes in younger women. Girls and young women are rapidly gaining strong bones, reaching peak density at the hip bone during the teen years, and peak density in the spine bones during the 20s or 30s.
The average spine bone density was 1.009 g/cm2 in Canadian, randomly chosen, teen women2, ages 16-19. In our meta-analysis, we found those taking CHC had a bone loss of 0.02 g/cm2 over two years. Although the difference in bone change was small, it was very significant (P = 0.0006). It was, however, also quite variable between studies likely because of racial and country differences. We did the necessary tests and they showed that these results were reliable.
How could CHC relate to teen women gaining less bone?
We believe that CHC is preventing bone growth in adolescent women. To understand this, we need to consider how we believe estrogen to normally affect bone. In adult women, estrogen is a strong and positive hormone for preventing bone loss (or resorption)3. However, adult bone change processes (called remodeling or renovating) are different than teenage bone change processes (called modeling or growth).
Adult bone goes through changes related to two linked processes that are ideally in balance. The first part is to remove old bone (called bone resorption) and the second process is to replace the old bone with new bone (bone formation)3. Because these two bone remodeling processes are linked together, when estrogen slows bone resorption, it also slows bone formation.
During the teen years and leading to peak bone density, all of the bone change is in growth. But estrogen, especially in a high dose, slows bone change. Therefore, high-dose estrogen prevents bone growth. Why do we say “high-dose”? Because the CHC is high compared to the level of hormones during the normal menstrual cycle—even “low dose CHC” or the typical 20 microgram ethinyl estradiol pill, to be effective contraception, provides about four times higher levels of hormone than the ovary normally produces. This is similar to something we already know: estrogen therapy, in a young girl who has not had her first period, would prevent her from growing taller. In adolescent girls, estrogen therapy stops growth that happens at the ends of arms and legs; this is called too early (or premature) closure of bone epiphyses.
Why didn’t we already know about the effects of CHC on teen bones?
One reason is that, in the past, CHC was not used by teenagers. When “The Pill” was first created, it was only prescribed to married women and, usually, these women were more than 20 years old. In the late 1990s, for example, CeMCOR reported the results from the Canadian Multicentre Osteoporosis Study (CaMos) which analyzed baseline bone density and use of CHC for about 500 premenopausal women ages 25-45 4. At that time, the average age women reported starting to use CHC was 20 years4. However, when we recruited women ages 16-24 years to a Youth CaMos Cohort in 2004-20062, we found that 75% of these young women had used CHC and that their average age at starting CHC was 17.5 years 5.
Another reason we did not know about the negative teen bone effects of CHC was that the original studies of CHC just assumed that it would be positive for bone, since it was already known that estrogen therapy increased bone density in adult women. The regulatory agencies did not require CHC investigators to study bone, so they didn’t. From the first CHC prescriptions in the 1960s until 1995 6, no one had studied bone change in younger women taking CHC and those not taking it. And, given that the strongest scientific evidence is a randomized, placebo-controlled trial (RCT), it is important to know that there still has not been an RCT studying bone changes of non-sexually active, adolescent women taking CHC or placebo.
One of the main reasons we’re just learning of a negative effect of CHC in adolescent women, is because CHC has provided birth control benefits to hundreds of millions of women and has never been questioned. It is controversial to say or to write anything negative about “The Pill.”CHC use, most recently, has been advocated by many medical organizations for its “non-contraceptive benefits” including for bones 7,8. Family doctors commonly prescribe CHC to help with teen pimples, cramps and irregular cycles. And it does, temporarily, help with these real problems. However, all of these issues improve during later adolescence and young adulthood, as teen menstrual cycles mature and are more likely to be ovulatory (egg-releasing) 9.
What should you do if you are an adolescent considering taking “The Pill”?
If you need birth control then it is wise to either use a barrier method plus vaginal spermicide, or a copper IUD.
If you don’t need contraception, then try to avoid CHC until you are in your 20s. CHC was designed for preventing pregnancy. CHC, when taken as prescribed, prevents pregnancy very well.
But there are alternative, effective, and likely healthier, ways to deal with the other common reasons teens take CHC:
2019/11—Reviewed by Sue F Seward, Dharani Kalidasan MSc, and Sonia Shirin MD
*CeMCOR paid $ Canadian 5,481.00 to allow the Clinical Endocrinology article to be “open access” and freely available—please share.
1. Goshtasebi A, Subotic Brajic T, Scholes D, Beres Lederer Goldberg T, Berenson A, Prior JC. Adolescent Use of Combined Hormonal Contraception and Peak Bone Mineral Density Accrual: a meta-analysis of international prospective controlled studies. Clin Endocrinol (Oxf) 2019.
2. Zhou W, Langsetmo L, Berger C, et al. Normative bone mineral density z-scores for Canadians aged 16 to 24 years: the Canadian Multicenter Osteoporosis Study. J Clin Densitom 2010; 13(3): 267-76.
3. Prior JC. Progesterone for the Prevention and Treatment of Osteoporosis in Women. Climacteric 2018; 21: 366-74.
4. Prior JC, Kirkland S, Joseph L, et al. Oral contraceptive agent use and bone mineral density in premenopausal women: cross-sectional, population-based data from the Canadian Multicentre Osteoporosis Study. Canadian Medical Association Journal 2001; 165: 1023-9.
5. Brajic TS, Berger C, Schlammerl K, et al. Combined hormonal contraceptives use and bone mineral density changes in adolescent and young women in a prospective population-based Canada-wide observational study. J Musculoskelet Neuronal Interact 2018; 18: 227-36.
6. Polatti F, Perotti F, Filippa N, Gallina D, Nappi RE. Bone mass and long-term monophasic oral contraceptive treatment in young women. Contraception 1995; 51: 221-4.
7. Jones RK. Beyond birth control: the overlooked benefits of oral contraceptive pills. New York: New York: Guttmacher Institute, 2011.
8. Armstrong C. ACOG guidelines on noncontraceptive use of hormonal contraceptives. Obstet and Gynecol 2010; 82: 294-5.
9. Prior JC. Adolescents' Use of Combined Hormonal Contraceptives for Menstrual Cycle-Related Problem Treatment and Contraception: Evidence of Potential Lifelong Negative Reproductive and Bone Effects. Women's Reproductive Health 2016; 3(2): 73-92.