Table 2.

Characteristics of participants, stratified by breast cancer

Controls (n = 10,520)Breast cancer cases (n = 589)
Characteristicn (%)n (%)
Age in years, median (range)67 (50–81)67 (50–79)
Education
 ≤High school3,761 (35.8)179 (30.4)a
 >High school6,759 (64.2)410 (69.6)
Annual family income
 <$35,0004,674 (45.4)217 (37.5)a
 ≥$35,0005,630 (54.6)361 (62.5)
Family history of breast cancer
 No8,534 (81.1)454 (77.1)a
 Yes1,986 (18.9)135 (22.9)
METs·hour·week−1b7.50 (0–134.17)7.00 (0–81.67)
METs·hour·week−1b
 ≥10.04,415 (42.0)243 (41.3)
 <10.06,105 (58.0)346 (58.7)
Number of cigarettes smoked per day
 ≤155,960 (56.7)278 (47.2)a
 >154,560 (43.3)311 (52.8)
Depressive symptomc, median (range)0.002 (0–0.937)0.002 (0.001–0.880)
Dietary alcohol per day in g, median (range)1.06 (0–183.76)1.88 (0–127.15)a
% calories from SFA, median (range)11.29 (2.22–32.39)11.49 (3.73–21.50)
% calories from SFAd
 <7.0%960 (9.1)50 (8.5)
 ≥7.0%9,560 (90.9)539 (91.5)
BMI in kg/m2, median (range)26.85 (15.42–58.49)28.00 (17.55–49.31)a
BMIe
 <30.0 kg/m27,505 (71.3)357 (60.6)a
 ≥30.0 kg/m23,015 (28.7)232 (39.4)
Waist-to-hip ratio, median (range)0.81 (0.44–1.39)0.81 (0.64–1.26)
Waist-to-hip ratio
 ≤0.857,514 (71.4)398 (67.6)a
 >0.853,006 (28.6)191 (32.4)
Age at menarche in years, median (range)13 (≤9–≥17)12 (≤9–≥17)a
Hysterectomy ever
 No6,739 (64.1)414 (70.3)a
 Yes3,781 (35.9)175 (29.7)
Age at menopause in years, median (range)50 (20–60)50 (21–63)
Oral contraceptive duration in years, median (range)5.7 (0.1–47.0)5.2 (0.1–21.0)a
Exogenous estrogen use (E-only use)
 Never7,360 (70.0)451 (76.6)a
 <5 years1,481 (14.1)58 (9.8)
 5 to < 10 years546 (5.2)18 (3.1)
 10 + years1,133 (10.8)62 (10.5)
Exogenous estrogen use (E + P use)
 Never8,681 (82.5)454 (77.1)a
 <5 years1,010 (9.6)73 (12.4)
 5 to <10 years434 (4.1)30 (5.1)
 10 to <15 years244 (2.3)21 (3.6)
 ≥15 years151 (1.4)11 (1.9)
  • aP < 0.05, χ2 or Wilcoxon rank-sum test.

  • bPhysical activity was estimated from recreational physical activity combining walking and mild, moderate, and strenuous physical activity. Each activity was assigned an MET value corresponding to intensity; the total MET·hours·week−1 was calculated by multiplying the MET level for the activity by the hours exercised per week and summing the values for all activities. The total MET was stratified into 2 groups, with 10 METs as the cutoff according to current American College of Sports Medicine and American Heart Association recommendations (43).

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

  • dPercentage of calories from SFA was stratified using 7% as the cutoff value according to the American Heart Association/American College of Cardiology dietary guidelines, which are aligned with the 2015–2020 Dietary Guidelines for Americans to help cardiovascular and metabolic disease reductions (44).

  • eBMI was categorized using the cutoff of 30 kg/m2; BM ≥ 30.0 is considered obese (https://www.cdc.gov/obesity/adult/defining.html).