Table 1.

Baseline (1993-1998) characteristics of participants in the WHIOS by region of residence at baseline among women included in the analysis of breast cancer incidence and geographic region of residence (n = 71,662)

Southern
Middle
Northern
P
n (%)n (%)n (%)
Age at baseline, y<0.001
    50-598,779 (35)4,795 (35)10,074 (31)
    60-6910,816 (43)5,825 (42)15,084 (47)
    70-795,759 (23)3,275 (24)7,255 (22)
Race/ethnicity<0.001
    Caucasian19,611 (77)11,787 (85)29,378 (91)
    African American1,908 (8)1,172 (8)1,989 (6)
    Hispanic1,731 (7)271 (2)421 (1)
    American Indian162 (0.6)47 (0.3)69 (0.2)
    Asian/Pacific Islander1,555 (6)385 (3)216 (0.7)
    Unknown387 (2)233 (2)340 (1)
Education<0.001
    0-8 y533 (2)84 (0.6)291 (0.9)
    Some high school867 (3)326 (2)1,001 (3)
    High school diploma/GED3,705 (15)1,652 (12)6,115 (19)
    School after high school9,938 (37)4,889 (35)11,152 (34)
    College degree or higher10,311 (41)6,944 (50)13,854 (43)
Family history of breast cancer<0.001
    Yes4,342 (17)2,540 (18)6,021 (19)
    No19,922 (79)10,726 (77)25,072 (77)
    Missing1,090 (4)629 (5)1,320 (4)
Age at menarche, y0.004
    ≤115,501 (22)3,069 (22)7,215 (22)
    12-1313,946 (55)7,806 (56)17,948 (55)
    ≥145,907 (23)3,020 (22)7,250 (22)
Age at menopause, y<0.001
    20-29258 (1)102 (0.7)144 (0.4)
    30-392,348 (9)1,071 (8)2,157 (7)
    40-4910,525 (42)5,368 (39)11,957 (37)
    50-6012,223 (48)7,354 (53)18,155 (56)
Age at first birth, y<0.001
    Never pregnant2,383 (9)1,432 (10)3,281 (10)
    No term pregnancy770 (3)445 (3)701 (2)
    <203,439 (14)1,480 (11)2,949 (9)
    20-2411,360 (45)5,831 (42)15,053 (46)
    25-295,623 (22)3,449 (25)7,941 (25)
    30-341,358 (5)945 (7)1,918 (6)
    35-393,56 (1)269 (2)478 (1)
    40-4460 (0.2)41 (0.3)88 (0.3)
    45+5 (0.02)3 (0.02)4 (0.01)
No of term pregnancies<0.001
    Never pregnant2,383 (9)1,432 (10)3,281 (10)
    Never had term pregnancy770 (3)445 (3)701 (2)
    12,510 (10)1,386 (10)2,495 (8)
    27,246 (29)3,825 (28)7,993 (25)
    36,137 (24)3,309 (24)7,993 (25)
    43,549 (14)1,924 (14)4,965 (15)
    5+2,759 (11)1,574 (11)4,985 (15)
Weight quintiles, kg<0.001
    Quintile 1: <58.75,647 (22)2,786 (20)5,870 (18)
    Quintile 2: ≥58.7 to <65.05,279 (21)2,860 (21)6,405 (20)
    Quintile 3: ≥ 65.0 to <71.84,926 (19)2,747 (20)6,511 (20)
    Quintile 4: ≥71.8 to <81.94,776 (19)2,725 (20)6,742 (21)
    Quintile 5: ≥81.94,726 (19)2,777 (20)6,885 (21)
Body mass index, kg/m2*<0.001
    Underweight (<18.5)377 (2)166 (1)302 (0.9)
    Normal (≥18.5 to 24.9)10,843 (43)5,884 (43)12,155 (38)
    Overweight (25.0-29.9)8,369 (33)4,549 (33)11,361 (35)
    Obesity I (30.0-34.9)3,571 (14)2,014 (15)5,277 (16)
    Obesity II (35.0-39.9)1,247 (5)722 (5)2,023 (6)
    Extreme obesity III (≥40)785 (3)446 (3)1,106 (3)
Recreational Physical activity quintiles, MET h/wk<0.001
    Quintile 1: <2.05,519 (22)2,432 (18)6,491 (20)
    Quintile 2: ≥2.0 to < 7.24,859 (19)2,635 (19)6,595 (20)
    Quintile 3: ≥7.2 to < 13.55,082 (20)2,873 (21)6,764 (21)
    Quintile 4: ≥13.5 to <23.34,823 (19)2,941 (21)6,525 (20)
    Quintile 5: ≥23.35,071 (20)3,014 (22)6,038 (19)
Hormone therapy duration of use, y<0.001
    None7,278 (29)4,242 (31)14,714 (45)
    <55,872 (23)3,394 (24)7,100 (22)
    5 to <104,089 (16)2,204 (16)4,160 (13)
    10+8,115 (32)4,055 (29)6,439 (20)
Alcohol intake<0.001
    Nondrinker4,084 (16)1,145 (8)2,407 (7)
    Past drinker4,897 (19)2,427 (17)5,483 (17)
    <1 drink per month2,717 (11)1,503 (11)4,092 (13)
    <1 drink per week4,615 (18)2,827 (20)7,035 (22)
    1 to <7 drinks per week5,886 (23)3,829 (28)9,303 (29)
    7+ drinks per week3,155 (12)2,164 (16)4,093 (13)
Vitamin D intake from foods quintiles, energy adjusted IU/d<0.001
    Quintile 1: <88.05,708 (23)2,917 (21)5,707 (18)
    Quintile 2: ≥88.0 to <123.75,386 (21)2,848 (21)6,099 (19)
    Quintile 3: ≥123.7 to <163.95,191 (20)2,774 (20)6,367 (20)
    Quintile 4: ≥163.9 to <227.74,776 (19)2,740 (20)6,817 (21)
    Quintile 5: ≥227.74,293 (17)2,616 (19)7,423 (23)
Vitamin D intake from foods and supplements quintiles, energy adjusted IU/d<0.001
    Quintile 1: <123.45,765 (23)2,798 (20)5,769 (18)
    Quintile 2: ≥123.4 to <222.75,094 (20)2,704 (19)6,535 (20)
    Quintile 3: ≥222.7 to <450.64,574 (18)2,864 (21)6,894 (21)
    Quintile 4: ≥450.6 to <622.84,864 (19)2,841 (20)6,628 (20)
    Quintile 5: ≥622.85,057 (20)2,688 (19)6,587 (20)
  • NOTE: P value from a χ2 test comparing baseline characteristics by region of residence at baseline.

  • * There is missing data for these variables, resulting in ns that do not add up to 71,662. Missing persons were not included in χ.