Table 1.
Birth cohort (year of birth) | <1946 | 1946–1950 | 1951–1955 | >1955 | Total | ||||
---|---|---|---|---|---|---|---|---|---|
Characteristics/smoking status | Ever | Never | Ever | Never | Ever | Never | Ever | Never | |
Subjects | 34,950 | 35,088 | 49,165 | 30,067 | 57,766 | 32,997 | 37,481 | 25,351 | 302,865 |
Agea, (mean), SD | 50 ± 12 | 54 ± 14 | 42 ± 3 | 42 ± 3 | 42 ± 3 | 42 ± 3 | 39 ± 5 | 38 ± 6 | 44 ± 9 |
Person years of follow-up | 657,363 | 654,555 | 781,699 | 480,232 | 665,721 | 381,025 | 325,583 | 218,137 | 4,164,314 |
Number of primary invasive breast cancers | 1,226 | 1,136 | 1,620 | 927 | 1,232 | 713 | 384 | 252 | 7,490 |
Follow-up years, (median) | 19 | 19 | 16 | 16 | 12 | 12 | 9 | 9 | 14 |
≥13 years of education (%) | 10 | 14 | 14 | 29 | 18 | 38 | 16 | 35 | 21 |
Age at diagnosis, (mean), SD | 61 ± 9 | 63 ± 11 | 52 ± 5 | 52 ± 5 | 49 ± 4 | 49 ± 5 | 46 ± 4 | 46 ± 4 | 54 ± 9 |
Nulliparous women | 4,456 | 5,112 | 4,496 | 3,210 | 6,272 | 3,738 | 4,929 | 4,310 | 36,523 |
Parous women | 30,494 | 29,976 | 44,669 | 26,857 | 51,494 | 29,259 | 32,552 | 21,041 | 266,342 |
Number of children, (mean), SD | 2 ± 2 | 2 ± 2 | 2 ± 1 | 2 ± 1 | 2 ± 1 | 2 ± 1 | 2 ± 1 | 2 ± 1 | 2 ± 1 |
Age at first childbirth, (mean), SD | 24 ± 4 | 25 ± 5 | 23 ± 4 | 24 ± 4 | 23 ± 5 | 25 ± 5 | 24 ± 5 | 26 ± 5 | 24 ± 5 |
Age at smoking initiationb (year), SD | 24 ± 8 | NA | 21 ± 5 | NA | 19 ± 5 | NA | 17 ± 3 | NA | 20 ± 6 |
Age at smoking initiation among nulliparousb (year), SD | 24 ± 7 | NA | 21 ± 5 | NA | 19 ± 4 | NA | 18 ± 4 | NA | 20 ± 6 |
Women smoking before first childbirthb (%) | 62 | NA | 63 | NA | 81 | NA | 94 | NA | 76 |
Body mass indexa (kg/m²) | 25 | 26 | 24 | 24 | 24 | 25 | 25 | 25 | 25 |
Level of physical activity, heavya,c (%) | 11 | 12 | 10 | 12 | 31 | 33 | 27 | 32 | 21 |
Smoking statusa (%) | 50 | 50 | 62 | 38 | 64 | 36 | 60 | 40 | 59 |
Ever smoker: current or former daily smokers
SD standard deviation, NA not applicable
aAt enrollment, bInformation not available for all smokers, cLight sports or heavy gardening ≥4 h per week, heavy exercise or daily competitive sports