Oral contraceptive use increases bone density and reduces the risk of osteoporosis.

Osteoporotic fractures, largely resulting from reduced estrogen levels after menopause and subsequent bone loss, are a leading cause of disability among older women. Although oral contraceptive pills (OCPs) contain estrogen, their long-term impact on bone health and osteoporosis risk remain uncertain. Here, we assessed the effect of OCP use on bone mineral density (BMD) and osteoporosis using data from 257,185 women from the UK Biobank, born 1936-1970. Time-dependent Cox regression was used to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (CI) for osteoporosis, while multivariable linear regression was used to assess the effect of OCP use on BMD, measured as T-scores in standard deviation units based on quantitative ultrasound of the calcaneus. By the end of follow-up in 2020, 7.6% of the participants had received an osteoporosis diagnosis. The rate of osteoporosis was lower among ever OCP users (HR = 0.86; 95% CI 0.83-0.89; P = 2.8 × 10-17). OCP use was also associated with a higher BMD T-score (0.052; 0.038-0.067; P = 2.1 × 10-12) with an increasing effect with longer use. Use of OCPs for 0-1 years had no significant effect on BMD (P = 0.081). However, longer durations were associated with increased BMD T-scores compared to never users: 2-5 years (0.046; 0.027-0.065, P = 2.2 × 10-6), 6-10 years (0.062; 0.043-0.080; P = 3.5 × 10-12), 11-15 years (0.062; 0.042-0.081; P = 3.2 × 10-12) and 16 + years (0.064; 0.044-0.083; P = 1.2 × 10-10). We found prior OCP use to be associated with higher BMD and a reduced risk of osteoporosis, potentially offering long-term benefits and suggesting that OCP use could reduce osteoporotic complications in older women.