Table 2.

Distribution of selected characteristics of study population (N = 102,098) at cohort enrollment, given as mean (±SD) and (%), by smoking status, Norwegian-Swedish Cohort Study, 1991-2000

CharacteristicsCurrent smokers (n = 28,624)Past smokers (n = 36,701)Passive smokers (n = 24,030)Never smokers (n = 12,743)P*
Age (y)40.5 ± 5.040.1 ± 4.940.6 ± 5.240.1 ± 5.5<0.001
Age at diagnosis (y)48.6 ± 5.247.4 ± 5.248.0 ± 5.447.9 ± 5.50.04
Education (y)11.4 ± 2.912.1 ± 3.112.6 ± 3.213.2 ± 3.2<0.001
Age at menarche (y)13.1 ± 1.413.1 ± 1.313.1 ± 1.413.1 ± 1.30.98
Postmenopausal (%)7.24.24.33.6<0.001
Age at menopause (y)42.4 ± 4.741.9 ± 4.742.8 ± 4.743.0 ± 4.30.09
Family history of breast cancer (%)§4.94.84.94.90.41
Parous (%)87.990.088.084.90.001
Age at first birth (y)22.9 ± 4.224.0 ± 4.424.5 ± 4.225.4 ± 4.20.001
No. of children2.0 ± 1.12.0 ± 1.12.1 ± 1.12.0 ± 1.20.001
Ever hormonal contraceptive use (%)76.776.868.365.4<0.001
Teetotalers (%)15.016.725.1v33.0<0.001
Alcohol consumption (g/d)4.6 ± 6.54.2 ± 5.63.3 ± 4.22.9 ± 3.6<0.001
Mean physical activity score3.0 ± 0.93.1 ± 0.93.1 ± 0.93.2 ± 0.9<0.001
BMI** at enrollment23.1 ± 3.523.2 ± 3.423.5 ± 3.623.0 ± 3.30.02
  • * Differences between current and never smoking groups.

  • Differences between current and past smoking groups (P < 0.001).

  • T-test/χ2 test for differences between passive and never smoking groups (P ≤ 0.01).

  • § Among mother or sister(s).

  • Among drinkers.

  • Leisure time physical activity in the year preceding cohort enrollment (scored as 1-5, low to high level).

  • ** BMI: the weight in kilograms divided by the square of the heights in meters.