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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 
    50-59 8,779 (35) 4,795 (35) 10,074 (31)  
    60-69 10,816 (43) 5,825 (42) 15,084 (47)  
    70-79 5,759 (23) 3,275 (24) 7,255 (22)  
Race/ethnicity    <0.001 
    Caucasian 19,611 (77) 11,787 (85) 29,378 (91)  
    African American 1,908 (8) 1,172 (8) 1,989 (6)  
    Hispanic 1,731 (7) 271 (2) 421 (1)  
    American Indian 162 (0.6) 47 (0.3) 69 (0.2)  
    Asian/Pacific Islander 1,555 (6) 385 (3) 216 (0.7)  
    Unknown 387 (2) 233 (2) 340 (1)  
Education    <0.001 
    0-8 y 533 (2) 84 (0.6) 291 (0.9)  
    Some high school 867 (3) 326 (2) 1,001 (3)  
    High school diploma/GED 3,705 (15) 1,652 (12) 6,115 (19)  
    School after high school 9,938 (37) 4,889 (35) 11,152 (34)  
    College degree or higher 10,311 (41) 6,944 (50) 13,854 (43)  
Family history of breast cancer    <0.001 
    Yes 4,342 (17) 2,540 (18) 6,021 (19)  
    No 19,922 (79) 10,726 (77) 25,072 (77)  
    Missing 1,090 (4) 629 (5) 1,320 (4)  
Age at menarche, y    0.004 
    ≤11 5,501 (22) 3,069 (22) 7,215 (22)  
    12-13 13,946 (55) 7,806 (56) 17,948 (55)  
    ≥14 5,907 (23) 3,020 (22) 7,250 (22)  
Age at menopause, y    <0.001 
    20-29 258 (1) 102 (0.7) 144 (0.4)  
    30-39 2,348 (9) 1,071 (8) 2,157 (7)  
    40-49 10,525 (42) 5,368 (39) 11,957 (37)  
    50-60 12,223 (48) 7,354 (53) 18,155 (56)  
Age at first birth, y    <0.001 
    Never pregnant 2,383 (9) 1,432 (10) 3,281 (10)  
    No term pregnancy 770 (3) 445 (3) 701 (2)  
    <20 3,439 (14) 1,480 (11) 2,949 (9)  
    20-24 11,360 (45) 5,831 (42) 15,053 (46)  
    25-29 5,623 (22) 3,449 (25) 7,941 (25)  
    30-34 1,358 (5) 945 (7) 1,918 (6)  
    35-39 3,56 (1) 269 (2) 478 (1)  
    40-44 60 (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 pregnant 2,383 (9) 1,432 (10) 3,281 (10)  
    Never had term pregnancy 770 (3) 445 (3) 701 (2)  
    1 2,510 (10) 1,386 (10) 2,495 (8)  
    2 7,246 (29) 3,825 (28) 7,993 (25)  
    3 6,137 (24) 3,309 (24) 7,993 (25)  
    4 3,549 (14) 1,924 (14) 4,965 (15)  
    5+ 2,759 (11) 1,574 (11) 4,985 (15)  
Weight quintiles, kg    <0.001 
    Quintile 1: <58.7 5,647 (22) 2,786 (20) 5,870 (18)  
    Quintile 2: ≥58.7 to <65.0 5,279 (21) 2,860 (21) 6,405 (20)  
    Quintile 3: ≥ 65.0 to <71.8 4,926 (19) 2,747 (20) 6,511 (20)  
    Quintile 4: ≥71.8 to <81.9 4,776 (19) 2,725 (20) 6,742 (21)  
    Quintile 5: ≥81.9 4,726 (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: <2.0 5,519 (22) 2,432 (18) 6,491 (20)  
    Quintile 2: ≥2.0 to < 7.2 4,859 (19) 2,635 (19) 6,595 (20)  
    Quintile 3: ≥7.2 to < 13.5 5,082 (20) 2,873 (21) 6,764 (21)  
    Quintile 4: ≥13.5 to <23.3 4,823 (19) 2,941 (21) 6,525 (20)  
    Quintile 5: ≥23.3 5,071 (20) 3,014 (22) 6,038 (19)  
Hormone therapy duration of use, y    <0.001 
    None 7,278 (29) 4,242 (31) 14,714 (45)  
    <5 5,872 (23) 3,394 (24) 7,100 (22)  
    5 to <10 4,089 (16) 2,204 (16) 4,160 (13)  
    10+ 8,115 (32) 4,055 (29) 6,439 (20)  
Alcohol intake    <0.001 
    Nondrinker 4,084 (16) 1,145 (8) 2,407 (7)  
    Past drinker 4,897 (19) 2,427 (17) 5,483 (17)  
    <1 drink per month 2,717 (11) 1,503 (11) 4,092 (13)  
    <1 drink per week 4,615 (18) 2,827 (20) 7,035 (22)  
    1 to <7 drinks per week 5,886 (23) 3,829 (28) 9,303 (29)  
    7+ drinks per week 3,155 (12) 2,164 (16) 4,093 (13)  
Vitamin D intake from foods quintiles, energy adjusted IU/d    <0.001 
    Quintile 1: <88.0 5,708 (23) 2,917 (21) 5,707 (18)  
    Quintile 2: ≥88.0 to <123.7 5,386 (21) 2,848 (21) 6,099 (19)  
    Quintile 3: ≥123.7 to <163.9 5,191 (20) 2,774 (20) 6,367 (20)  
    Quintile 4: ≥163.9 to <227.7 4,776 (19) 2,740 (20) 6,817 (21)  
    Quintile 5: ≥227.7 4,293 (17) 2,616 (19) 7,423 (23)  
Vitamin D intake from foods and supplements quintiles, energy adjusted IU/d    <0.001 
    Quintile 1: <123.4 5,765 (23) 2,798 (20) 5,769 (18)  
    Quintile 2: ≥123.4 to <222.7 5,094 (20) 2,704 (19) 6,535 (20)  
    Quintile 3: ≥222.7 to <450.6 4,574 (18) 2,864 (21) 6,894 (21)  
    Quintile 4: ≥450.6 to <622.8 4,864 (19) 2,841 (20) 6,628 (20)  
    Quintile 5: ≥622.8 5,057 (20) 2,688 (19) 6,587 (20)  
Southern
Middle
Northern
P
n (%)n (%)n (%)
Age at baseline, y    <0.001 
    50-59 8,779 (35) 4,795 (35) 10,074 (31)  
    60-69 10,816 (43) 5,825 (42) 15,084 (47)  
    70-79 5,759 (23) 3,275 (24) 7,255 (22)  
Race/ethnicity    <0.001 
    Caucasian 19,611 (77) 11,787 (85) 29,378 (91)  
    African American 1,908 (8) 1,172 (8) 1,989 (6)  
    Hispanic 1,731 (7) 271 (2) 421 (1)  
    American Indian 162 (0.6) 47 (0.3) 69 (0.2)  
    Asian/Pacific Islander 1,555 (6) 385 (3) 216 (0.7)  
    Unknown 387 (2) 233 (2) 340 (1)  
Education    <0.001 
    0-8 y 533 (2) 84 (0.6) 291 (0.9)  
    Some high school 867 (3) 326 (2) 1,001 (3)  
    High school diploma/GED 3,705 (15) 1,652 (12) 6,115 (19)  
    School after high school 9,938 (37) 4,889 (35) 11,152 (34)  
    College degree or higher 10,311 (41) 6,944 (50) 13,854 (43)  
Family history of breast cancer    <0.001 
    Yes 4,342 (17) 2,540 (18) 6,021 (19)  
    No 19,922 (79) 10,726 (77) 25,072 (77)  
    Missing 1,090 (4) 629 (5) 1,320 (4)  
Age at menarche, y    0.004 
    ≤11 5,501 (22) 3,069 (22) 7,215 (22)  
    12-13 13,946 (55) 7,806 (56) 17,948 (55)  
    ≥14 5,907 (23) 3,020 (22) 7,250 (22)  
Age at menopause, y    <0.001 
    20-29 258 (1) 102 (0.7) 144 (0.4)  
    30-39 2,348 (9) 1,071 (8) 2,157 (7)  
    40-49 10,525 (42) 5,368 (39) 11,957 (37)  
    50-60 12,223 (48) 7,354 (53) 18,155 (56)  
Age at first birth, y    <0.001 
    Never pregnant 2,383 (9) 1,432 (10) 3,281 (10)  
    No term pregnancy 770 (3) 445 (3) 701 (2)  
    <20 3,439 (14) 1,480 (11) 2,949 (9)  
    20-24 11,360 (45) 5,831 (42) 15,053 (46)  
    25-29 5,623 (22) 3,449 (25) 7,941 (25)  
    30-34 1,358 (5) 945 (7) 1,918 (6)  
    35-39 3,56 (1) 269 (2) 478 (1)  
    40-44 60 (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 pregnant 2,383 (9) 1,432 (10) 3,281 (10)  
    Never had term pregnancy 770 (3) 445 (3) 701 (2)  
    1 2,510 (10) 1,386 (10) 2,495 (8)  
    2 7,246 (29) 3,825 (28) 7,993 (25)  
    3 6,137 (24) 3,309 (24) 7,993 (25)  
    4 3,549 (14) 1,924 (14) 4,965 (15)  
    5+ 2,759 (11) 1,574 (11) 4,985 (15)  
Weight quintiles, kg    <0.001 
    Quintile 1: <58.7 5,647 (22) 2,786 (20) 5,870 (18)  
    Quintile 2: ≥58.7 to <65.0 5,279 (21) 2,860 (21) 6,405 (20)  
    Quintile 3: ≥ 65.0 to <71.8 4,926 (19) 2,747 (20) 6,511 (20)  
    Quintile 4: ≥71.8 to <81.9 4,776 (19) 2,725 (20) 6,742 (21)  
    Quintile 5: ≥81.9 4,726 (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: <2.0 5,519 (22) 2,432 (18) 6,491 (20)  
    Quintile 2: ≥2.0 to < 7.2 4,859 (19) 2,635 (19) 6,595 (20)  
    Quintile 3: ≥7.2 to < 13.5 5,082 (20) 2,873 (21) 6,764 (21)  
    Quintile 4: ≥13.5 to <23.3 4,823 (19) 2,941 (21) 6,525 (20)  
    Quintile 5: ≥23.3 5,071 (20) 3,014 (22) 6,038 (19)  
Hormone therapy duration of use, y    <0.001 
    None 7,278 (29) 4,242 (31) 14,714 (45)  
    <5 5,872 (23) 3,394 (24) 7,100 (22)  
    5 to <10 4,089 (16) 2,204 (16) 4,160 (13)  
    10+ 8,115 (32) 4,055 (29) 6,439 (20)  
Alcohol intake    <0.001 
    Nondrinker 4,084 (16) 1,145 (8) 2,407 (7)  
    Past drinker 4,897 (19) 2,427 (17) 5,483 (17)  
    <1 drink per month 2,717 (11) 1,503 (11) 4,092 (13)  
    <1 drink per week 4,615 (18) 2,827 (20) 7,035 (22)  
    1 to <7 drinks per week 5,886 (23) 3,829 (28) 9,303 (29)  
    7+ drinks per week 3,155 (12) 2,164 (16) 4,093 (13)  
Vitamin D intake from foods quintiles, energy adjusted IU/d    <0.001 
    Quintile 1: <88.0 5,708 (23) 2,917 (21) 5,707 (18)  
    Quintile 2: ≥88.0 to <123.7 5,386 (21) 2,848 (21) 6,099 (19)  
    Quintile 3: ≥123.7 to <163.9 5,191 (20) 2,774 (20) 6,367 (20)  
    Quintile 4: ≥163.9 to <227.7 4,776 (19) 2,740 (20) 6,817 (21)  
    Quintile 5: ≥227.7 4,293 (17) 2,616 (19) 7,423 (23)  
Vitamin D intake from foods and supplements quintiles, energy adjusted IU/d    <0.001 
    Quintile 1: <123.4 5,765 (23) 2,798 (20) 5,769 (18)  
    Quintile 2: ≥123.4 to <222.7 5,094 (20) 2,704 (19) 6,535 (20)  
    Quintile 3: ≥222.7 to <450.6 4,574 (18) 2,864 (21) 6,894 (21)  
    Quintile 4: ≥450.6 to <622.8 4,864 (19) 2,841 (20) 6,628 (20)  
    Quintile 5: ≥622.8 5,057 (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.

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