Table 2

RRs and 95% CIs of developing breast cancer according to use of OCs, The Women’s Lifestyle and Health Study

Use of OCsStudy populationBreast cancer casesRR (95% CI)
Age-adjustedMultivariatea
Never-users28,1712611.0 (reference)1.0 (reference)
Ever-users74,8567471.2 (1.1–1.4)1.3 (1.1–1.5)
Current/recent users at start of follow-up9,299911.6 (1.2–2.0)1.6 (1.2–2.1)
Former users at start of follow-up65,5576561.2 (1.1–1.4)1.2 (1.1–1.4)
Duration of use (yrs)
 <538,7423841.2 (1.0–1.4)1.2 (1.0–1.5)
 5–918,8761781.3 (1.0–1.5)1.2 (1.0–1.5)
 10–1410,8031131.4 (1.1–1.8)1.4 (1.1–1.8)
 15+5,441631.3 (1.0–1.8)1.3 (1.0–1.8)
Test for trendP = 0.001P = 0.005
  • 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.