Oral contraceptive use and risk of mortality among Norwegian women – a prospective study from the NOWAC study

Abstract

Millions of women are dependent on the use of oral contraceptives in order to have a more meaningful life and a general sense of well-being. These benefits make oral contraceptives one of the most prescribed medications among women. However, while there is established evidence on the short-term effects of oral contraceptive use, there are conflicting reports on the long-term risk of oral contraceptive use, especially regarding mortality. This study aims to explore the long-term association between oral contraceptive use and risk of mortality in a prospective cohort study of Norwegian women using the Cox proportional hazard model.

Methods: We gathered self-reported data from 126 786 women in the Norwegian Women and Cancer study's nationally representative cohort study. We obtained data on Oral contraceptive use, including duration of use and age at first use. Information on the outcome mortality was obtained from the Norwegian cause of death registry (which is regularly updated) during follow-up, in addition to covariate information. The association between Oral contraceptive use and the outcome mortality was assessed using Cox regression analysis. Respondents who had missing data on the exposure were excluded. Missing data on variables and participants lost to follow-up were excluded.

Results: Based on 11 310 deaths, we found no overall difference in mortality among women who had ever used oral contraceptives compared with women who had never used oral contraceptives. The hazard risk for ever-users, adjusted for age, was 0.95 (95% CI, 0.92 to 1.00). We observed a trend in no risk for total mortality with increasing duration of OC use of oral contraceptives. After adjusting for age, body mass index, cigarette smoking, education, physical activity, and the number of children, women who had used oral contraceptives still had no risk of mortality of 0.98 (CI, 0.95 to 1.02).

Conclusion The use of Oral contraceptives is safe; no evidence from this study indicates that long durations of oral contraceptive use adversely affect long-term risk for mortality.