Table 3

RRs and 95% CIs of developing breast cancer according to use of OCs, stratified on age at start of follow-up, The Women’s Lifestyle and Health Study

Use of OCsStudy populationBreast cancer casesRR (95% CI)
Age-adjustedMultivariatea
Age group 30–39 yrsb
 Never-users8,829411.0 (reference)1.0 (reference)
 Ever-users35,3652261.5 (1.1–2.1)1.5 (1.1–2.1)
 Current/recent users at start of follow-up6,626441.7 (1.0–2.0)1.7 (1.1–2.7)
 Former users at start of follow-up28,7391821.4 (1.0–2.0)1.5 (1.0–2.1)
Age group 40–49 yrs
 Never-users19,3422201.0 (reference)1.0 (reference)
 Ever-users39,4915211.2 (1.0–1.4)1.2 (1.0–1.4)
 Current/recent users at start of follow-up2,673471.7 (1.2–2.3)1.6 (1.2–2.3)
 Former users at start of follow-up36,8184741.2 (1.0–1.4)1.2 (1.0–1.4)
  • a Multivariate analysis adjusted for: age (continuous variable), parity (0, 1, 2, 3+), age at first birth (−20, 21–24, 25+), age at menarche (continuous variable), use of HRT (ever/never), menopausal status (pre-/postmenopausal), history of breast cancer in first-degree relatives (yes/no), duration of breastfeeding (continuous variable), BMI (continuous variable), region (Sweden and five health regions in Norway), and a term for interaction between BMI and menopausal status.

  • b Menopausal status and the interaction term between BMI and menopausal status were not included in the multivariate model.