Table 1.
Description of the environmental risk factors by case-control status from 23 studies in the BCAC
| Risk factor | Category | Cases | Controls | All |
|---|---|---|---|---|
| Reference age | N | 34,475 | 34,786 | 69,261 |
| N premenopausal | 13,954 | 14,532 | 28,486 | |
| N postmenopausal | 20,521 | 20,254 | 40,775 | |
| Mean (SD)a | 56.2 (11.2) | 55.5 (11.5) | 55.9 (11.4) | |
| Number of births (parity) | N b | 27,174 | 28,508 | 55,682 |
| Mean (SD)a | 1.9 (1.3) | 2.0 (1.3) | 1.9 (1.3) | |
| Age at menarche (menarche) | N b | 21,942 | 23,109 | 45,051 |
| Mean (SD)a | 13.1 (1.6) | 13.1 (1.6) | 13.1 (1.6) | |
| Adult body height (cm, height) | N b | 24,016 | 20,178 | 44,194 |
| Mean (SD)a | 164 (6.6) | 165 (6.6) | 164 (6.6) | |
| BMI (kg/m2, postmenopausal women, BMI post) | N b | 4,423 | 4,468 | 8,891 |
| Mean (SD)a | 25.2 (4.5) | 24.8 (4.2) | 25.0 (4.4) | |
| BMI (kg/m2, premenopausal women, BMI pre) | N b | 1,759 | 1,446 | 3,205 |
| Mean (SD)a | 24.7 (5.1) | 25.5 (5.6) | 25.0 (5.4) | |
| Use of oral contraceptives (years, oral contraceptive duration) | N b | 11,017 | 11,911 | 22,928 |
| Mean (SD)a | 5.3 (7.0) | 5.9 (7.1) | 5.6 (7.1) | |
| Estrogen-progesterone therapy (years, postm. women,a estrogen-progesterone therapy duration) | N b | 3,790 | 4,057 | 7,847 |
| Mean (SD)a | 1.7 (4.3) | 1.2 (3.7) | 1.4 (4.0) | |
| Estrogen therapy (years, postm. women,a estrogen therapy duration) | N b | 3,876 | 4,085 | 7,961 |
| Mean (SD)a | 1.3 (4.1) | 1.0 (3.5) | 1.1 (3.8) | |
| Alcohol consumption (grams per day, alcohol) | N b | 3,812 | 4,055 | 7,867 |
| Mean (SD)a | 7.3 (16.0) | 6.8 (11.3) | 7.1 (13.8) | |
| Family history of breast cancer (famhist) | N b | 20,108 | 18,522 | 38,630 |
| Yes (%) | 4,213 (21%) | 1,606 (9%) | 5,819 (15%) |
a
Women who stopped hormone therapy before diagnosis/interview were assigned 0 years of therapy.
b
N is the final sample size for analysis without individuals with unknown values in the variable or any of the adjustment variables.