Table 1.

Characteristics of participants, stratified by breast cancer

ControlsBreast cancer cases
(n = 6,215)(n = 352)
Characteristicn (%)n (%)
Age in years, median (range)67 (50–81)68 (50–79)
Family income
 <$35,0002,941 (48.3)155 (44.8)
 ≥$35,0003,145 (51.7)191 (55.2)
Family history of breast cancer
 No5,200 (83.7)275 (78.1)a
 Yes1,015 (16.3)77 (21.9)
Depressive symptomb, median (range)0.002 (0.000–0.919)0.002 (0.000–0.880)
Dietary alcohol per day in g, median (range)1.02 (0.00–153.60)1.57 (0.00–106.70)a
% calories from fat, median (range)33.58 (7.81–65.54)34.15 (11.71–60.35)
% calories from SFA, median (range)11.21 (2.22–30.80)11.76 (3.86–20.10)
METs·hour/weekc2.25 (0.00–142.30)0.63 (0.00–54.33)a
Smoking now
 No5,943 (95.6)331 (94.0)
 Yes272 (4.4)21 (6.0)
BMI in kg/m2, median (range)27.01 (15.42–58.49)28.30 (18.31–47.67)a
Waist-to-hip ratio, median (range)0.81 (0.44–1.26)0.82 (0.64–1.07)
Age at menarche in years, median (range)13 (≤9–≥17)12 (≤9–≥17)a
Age at menopause in years, median (range)50 (23–71)50 (21–63)
Number of pregnancies, median (range)3 (0–8)3 (0–8)
History of hysterectomy or oophorectomy
 No3,831 (61.6)241 (68.5)a
 Yes2,384 (38.4)111 (31.5)
Exogenous estrogen use (E only use)
 Never use4,427 (71.2)275 (78.1)a
 <5 years948 (15.3)32 (9.1)
 5 to <10 years303 (4.9)12 (3.4)
 10 to <15 years213 (3.4)15 (4.3)
 15+ years324 (5.2)18 (5.1)
Exogenous estrogen use (E + P use)
 Never use5,278 (84.9)276 (78.4)a
 <5 years582 (9.4)44 (12.5)
 5 to <10 years188 (3.0)16 (4.5)
 10 to <15 years99 (1.6)13 (3.7)
 15+ years68 (1.1)3 (0.9)
  • Abbreviations: BMI, body mass index; E, estrogen; E + P, estrogen + progestin; MET, metabolic equivalent; SFA, saturated fatty acids

  • aP < 0.05, χ2 or Wilcoxon rank-sum test.

  • bDepression scales were estimated using a short form of the Center for Epidemiologic Studies Depression Scale.

  • cPhysical activity was estimated from recreational physical activity combining walking and mild, moderate, and strenuous physical activity; each activity was assigned a MET value corresponding to intensity, and the total MET·hours/week was calculated by multiplying the MET level for the activity by the hours exercised per week and summing the values for all activities (46).