Table 2.

Baseline characteristics of the study population and of breast cancer cases

VITAL cohort (N = 30,797)Breast cancer cases (N = 899)
CharacteristicN (%)N (%)
Age
 50–546,981 (22.7)112 (12.5)
 55–597,648 (24.8)200 (22.3)
 60–645,725 (18.6)189 (21.0)
 65–694,810 (15.6)177 (19.7)
 70 or older5,633 (18.3)221 (24.6)
Education
 High school graduate/GED or below6,996 (22.7)210 (23.4)
 Some college/technical school12,791 (41.5)366 (40.7)
 College graduate6,866 (22.3)207 (23.0)
 Advanced degree4,012 (13.0)111 (12.4)
 Missing132 (0.4)5 (0.6)
Race
 White28,762 (93.4)858 (95.4)
 Non-white1,922 (6.2)37 (4.1)
 Missing113 (0.4)4 (0.4)
Mammogram in 2 years before baseline
 No2,606 (8.5)73 (8.1)
 Yes28,090 (91.2)824 (91.7)
 Missing101 (0.3)2 (0.2)
Family history of breast cancer (first degree)
 No25,738 (83.6)683 (76.0)
 Yes4,626 (15.0)192 (21.4)
 Missing433 (1.4)24 (2.7)
Age at menarche
 11 or younger5,736 (18.6)182 (20.2)
 129,129 (29.6)288 (32.0)
 138,966 (29.1)238 (26.5)
 143,984 (12.9)110 (12.2)
 15 or older2,716 (8.8)77 (8.6)
 Missing266 (0.9)4 (0.4)
Age when first child born
 19 or younger5,413 (17.6)135 (15.0)
 20–2412,557 (40.8)396 (44.1)
 25–295,999 (19.5)155 (17.2)
 30–342,019 (6.6)52 (5.8)
 35 or older629 (2.0)26 (2.9)
 No children3,883 (12.6)128 (14.2)
 Missing297 (1.0)7 (0.8)
Years of combined estrogen and progestin hormone therapy use
 None or less than 118,002 (58.5)472 (52.5)
 1–44,092 (13.3)92 (10.2)
 5–93,366 (10.9)123 (13.7)
 10 or more3,581 (11.6)157 (17.5)
 Missing1,756 (5.7)55 (6.1)
Age at menopause
 39 or younger2,909 (9.5)70 (7.8)
 40–444,041 (13.1)124 (13.8)
 45–498,208 (26.7)237 (26.4)
 50–5410,826 (35.2)333 (37.0)
 55 or older1,698 (5.5)60 (6.7)
 Perimenopausal at baseline978 (3.2)19 (2.1)
 Missing2,137 (6.9)56 (6.2)