Differential bone calcium retention with the use of oral versus vaginal hormonal contraception: A randomized trial...

This study aimed to assess if hormonal contraception administered orally (combined oral contraceptive pill, COC) or vaginally (contraceptive vaginal ring) differentially affected bone calcium retention in young females.

Reproductive aged females (18-35 years) not using hormonal contraception were dosed with 50 nCi ⁴¹Ca as CaCl₂ in 10 mL of sterile saline (0.9%). Following an equilibration phase of ≥100 days and a baseline of two menstrual cycles, participants used COC and the ring for two cycles (49 days) each, in a randomized order, separated and followed by washouts of two menstrual cycles. Twenty-four-hour urine samples were collected monthly during equilibration and every around 10 days during baseline, interventions, and washouts to assess bone calcium retention through accelerator mass spectrometry analysis of the ⁴¹Ca:Ca ratio in urine. The effect of each contraception was determined by comparing ⁴¹Ca:Ca measured during each contraception intervention to ⁴¹Ca:Ca measured during the "control" (baseline and washout) phases using linear models and generalized linear mixed models.

Eight reproductive aged females were studied. Compared with control phases (baseline and washouts), COC resulted in greater bone calcium retention (11.3%, 95% CI: 6.7%, 15.6%). The ring did not alter bone calcium retention (4.2%, 95% CI: -6.6%, 13.9%). COC produced a greater change in calcium retention than the ring (p = 0.03).

Although many factors contribute to bone health, short-term COC improved bone calcium retention, suggesting a potential benefit of COC to bone in females. Conversely, the ring did not alter calcium retention, and may be neither beneficial nor deleterious for bone.

In this study, the effects of oral (pill) vs. vaginal (ring) hormonal contraception on bone calcium retention were assessed in young females. The pill improved bone calcium retention, suggesting a potential beneficial effect on bone health; the ring did not change bone calcium retention compared with control (no contraception).