Combined hormonal oral contraceptives (CHC) have been around since the 1960’s. Concerns about the estrogen component in them and whether they impair bone formation in teenage girls has risen especially since this is the age that bone formation is so crucial.
Researchers conducted a meta-analysis (examined data from several independent studies on the same subject) to compare changes in bone density determined by duel-energy x-ray absorptiometry (DEXA) in healthy adolescent users and nonusers of estrogen-progestin CHC. There were 9 studies that involved a total of 1535 adolescents aged 12-19 years. Pooled analysis showed that the use of estrogen-progestin CHC was associated with significantly lower bone density at 24 months.

So even though findings confirm concerns that combined birth control pills negatively effect bone density in adolescents, I’m not sure we can blame it all on the estrogen component. The dose of hormone that may cause this effect wasn’t clear in the study. Even though the American Academy of Pediatrics are endorsing long-acting reversible contraceptive (LARC) options as being safer and effective, we need to remember that at least one progestin only option (Depo-provera) has been studied and was related to lower bone density. The contraceptive implant known as Nexplanon is also a synthetic progesterone. Both of these progestins are systemically absorbed which is why they are so effective in preventing pregnancy, but do they also effect bone density?

I believe it is still unclear which contraceptive method is best in reference to protecting bone health. We need to consider the costs and benefits of all of these methods. For instance, injectable contraceptives and implants provide effective longterm birth control yet do not involve a daily regimen. So for a women who may not remember or be able to take a pill at the same time daily, an oral birth control pill would not be the choice for her and would increase her risk of an unintended pregnancy. A LARC would be best for this particular patient but I would screen her for other risk factors for bone loss. This includes checking a Vitamin D level, evaluate her calcium and mineral intake as well as her gut health (to make sure she has healthy absorption), and increase weight bearing and strength training exercises.

Screening teens for bone health is always a good idea, but is essential for girls that desire ANY hormonal contraceptive. This will determine a baseline which then can be monitored yearly.

Lopez LM, Grimes DA, Schulz KF, Curtis KM; Chen M. Hormonal contraceptives and bone health in women. Cochrane.org.2014 June.
Goshtasebi A et al. Adolescent use of combined hormonal contraception and peak bone mineral density accrual: A meta-analysis of international prospective controlled studies. Clin Endocrinol (Oxf) 2019 Jan 7; [e-pub].