UC San Diego

Context

Oral contraceptive (OC) use is common, but bone changes associated with use of contemporary OC remain unclear.

Objective

The objective of the study was to compare bone mineral density (BMD) change in adolescent and young adult OC users and discontinuers of two estrogen doses, relative to nonusers.

Design and setting

This was a prospective cohort study, Group Health Cooperative.

Participants

Participants included 606 women aged 14-30 yr (50% adolescents aged 14-18 yr): 389 OC users [62% 30-35 μg ethinyl estradiol (EE)] and 217 age-similar nonusers; there were 172 OC discontinuers. The 24-month retention was 78%.

Main outcome measure

The main outcome measure was BMD measured at 6-month intervals for 24-36 months.

Results

After 24 months, adolescents using 30-35 μg EE OCs, but not those using lower-dose OCs, had significantly smaller adjusted mean percentage BMD gains than nonusers at the spine [group means (95% confidence interval for between group differences) 1.32 vs. 2.26% (-1.89, -0.13%)] and whole body [1.45 vs. 2.03% (-1.29%, -0.13%)]. Adolescents who discontinued 30-35 μg EE OC showed significantly smaller gains than nonusers at the spine after 12 months [0.51 vs. 1.72% (-2.38%, -0.30%)]. Young adult OC users did not differ from nonusers. However, OC discontinuers of both doses differed significantly from nonusers at the spine 12 months after discontinuation [-1.32% < 30 μg EE, -0.92% 30-35 μg EE vs. +0.27% nonusers (-2.48, -0.54, and -1.94%, -0.55%, respectively)]. Results were similar for mean absolute BMD change (grams per square centimeter).

Conclusions

Both OC use and discontinuation were associated with BMD losses/smaller gains relative to nonusers (differences < 2% after 12-24 months for all skeletal sites). The clinical significance of these results regarding future fracture risk is unknown. Study of longer-term trends after discontinuation is needed.