Hormonal contraception (HC) plays a crucial role in preventing pregnancies and managing certain health conditions. However, HC works by modulating hormones that are essential for bone health and preventing osteoporosis. Here’s a summary of how different types of hormonal contraception can impact bone density:
Oral Contraceptive Pill
- Adolescence: Using the oral contraceptive pill within three years of starting periods is associated with a slight decrease in bone density and an increased fracture risk in some studies. This is likely because, during adolescence, there is a surge in estrogen and growth hormone that rapidly increases bone density, both of which the pill can decrease.
- Adulthood: In adult women, the pill does not seem to impact bone density significantly.
- Peri-Menopause: The pill is associated with improving bone density during peri-menopause.
Progesterone-Only Contraception
The impact of progesterone-only contraception on bone density depends on how much it inhibits the production of estradiol, the main type of estrogen. Data suggest that estradiol levels need to be between 110 pmol/L and 165 pmol/L for bone protection.
- Mirena: Generally does not inhibit ovulation or estradiol production, and long-term studies do not show an increased risk of osteoporosis.
- Depo-Provera Injection: Significantly decreases estradiol levels and has been proven to decrease bone density and increase fracture risk.
- Implanon and New Progesterone-Only Pills (e.g., Slinda): Inhibit ovulation and decrease estrogen to early follicular levels, similar to the bone-safe range of 110-165 pmol/L. Studies on these types of contraception are mainly indirect, looking at bone density or bone turnover markers rather than fractures, and are not long-term enough to confirm or deny a negative impact on bone health confidently.
Clinical Observations
Clinically, some patients on progesterone-only contraception may have completely suppressed estradiol and low LH/FSH levels, which can negatively impact bone health. This could be due to Relative Energy Deficiency in Sport (RED-S) or individual responses to progesterone. Measuring estradiol levels in women on progesterone-only contraception, especially if there is concern for bone health, would be appropriate to ensure estrogen levels are within the bone-safe range.