Table 2.

Multivariate-adjusted RR of developing breast cancer among women in the NHSII according to smoking exposure updated during follow-up

Smoking variablesNo. casesPerson-yearsRR95% CIP for trend
Current status
    Never smokers596704,0231.00
    Past smokers283242,9161.181.02–1.36
    Current smokers128125,1381.120.92–1.37
Never smokers596704,0231.00
    1–4 cigarettes/day (current)1420,1060.770.44–1.33
    5–14 cigarettes/day (current)3734,1321.180.88–1.74
    15–24 cigarettes/day (current)5547,5211.140.90–1.61
    25+ cigarettes/day (current)2020,3080.980.69–1.700.4
Never smokers596704,0231.00
    1–4 cigarettes/day (past)6660,6041.210.94–1.56
    5–14 cigarettes/day (past)9474,3291.321.06–1.65
    15–24 cigarettes/day (past)7670,8541.040.82–1.33
    25+ cigarettes/day (past)4535,8351.120.82–1.530.6
Duration of smoking
    Never smokers596704,0231.00
    <10 years 5254,3541.140.85–1.52
    10–14 years99103,3591.190.96–1.48
    15–19 years96101,6871.060.85–1.33
    20+ years166114,1131.211.01–1.450.04
Age started smoking
    Never smokers (at baseline: 1989)603707,6861.00
    <15 years5553,5311.290.97–1.71
    15–19 years203200,6161.090.93–1.29
    20+ years148115,7031.180.97–1.42
Smoking duration before first pregnancy
    Never smokers596704,0231.00
    1–4 years3938,7041.020.72–1.44
    5–9 years112104,8161.120.91–1.39
    10–14 years119113,5021.190.97–1.47
    15–19 years8064,4471.421.10–1.83
    20+ years4935,7661.100.80–1.520.01
  • Note: Covariates: stratified by age and further adjusted for BMI, height, oral contraceptives, parity and age at first birth, age at menarche, family history of breast cancer, benign breast disease, alcohol consumption, and menopause status.