Table 5.
Association of BMI and breast cancer risk using observed body mass index (BMI)
| Breast cancer group | N/events | HR (95% CI) | P* |
|---|---|---|---|
| Per 5-kg/m2 increase in BMI at date of questionnaire | |||
| All participants (confounding adjustment sequentially) | |||
| Unadjusted | 7516/3594 | 0.92 (0.88 to 0.97) | 4.3 × 10-4 |
| Adjusted for principal components | 7516/3594 | 0.93 (0.89 to 0.97) | 7.3 × 10-4 |
| Additionally adjusted for country | 7516/3594 | 0.92 (0.88 to 0.96) | 3.1 × 10-4 |
| Additionally adjusted for birth cohort | 7516/3594 | 0.94 (0.90 to 0.98) | .003 |
| Additionally adjusted for mutation status | 7516/3594 | 0.95 (0.91 to 0.99) | .01 |
| Additionally adjusted for menopausal status | 7516/3594 | 0.94 (0.90 to 0.98) | .007 |
| Additionally adjusted for parity and age at menarche | 6964/3331 | 0.93 (0.89 to 0.98) | .003 |
| By mutation status† | |||
| BRCA1 carrier | 4401/2114 | 0.96 (0.91 to 1.01) | .11 |
| BRCA2 carrier | 3115/1480 | 0.90 (0.84 to 0.97) | .003 |
| Pinteraction‡ | .26 | ||
| By menopausal status§ | |||
| Premenopausal | 7516/2153 | 0.92 (0.87 to 0.97) | .001 |
| Postmenopausal | 3029/1389 | 0.97 (0.91 to 1.04) | .40 |
| Pinteraction‡ | .14 | ||
| Per 5-kg/m2 increase in BMI in young adulthood | |||
| All participants (confounding adjustment sequentially) | |||
| Unadjusted | 5417/2520 | 0.83 (0.76 to 0.91) | 3.1 × 10-5 |
| Adjusted for principal components | 5417/2520 | 0.83 (0.76 to 0.91) | 5.4 × 10-5 |
| Additionally adjusted for country | 5417/2520 | 0.81 (0.74 to 0.88) | 2.8 × 10-6 |
| Additionally adjusted for birth cohort | 5417/2520 | 0.81 (0.74 to 0.88) | 1.8 × 10-6 |
| Additionally adjusted for mutation status | 5417/2520 | 0.83 (0.76 to 0.90) | 1.7 × 10-5 |
| Additionally adjusted for menopausal status | 5417/2520 | 0.83 (0.76 to 0.90) | 2.1 × 10-5 |
| Additionally adjusted for parity and age at menarche | 5210/2436 | 0.82 (0.75 to 0.90) | 2.7 × 10-5 |
| By mutation status† | |||
| BRCA1 carrier | 3134/1462 | 0.87 (0.78 to 0.97) | .01 |
| BRCA2 carrier | 2283/1058 | 0.74 (0.63 to 0.85) | 4.5 × 10-5 |
| Pinteraction | .06 | ||
| By menopausal status‡ | |||
| Premenopausal | 5417/1519 | 0.85 (0.78 to 0.94) | .002 |
| Postmenopausal | 2181/977 | 0.79 (0.69 to 0.91) | .001 |
| Pinteraction | .35 | ||
*
P values calculated using weighted Cox models. All P values are two-sided; HR = hazard ratio; CI = confidence interval.
†
Adjusted for principal components, birth cohort, country of enrollment, and menopausal status.
‡
Adjusted for principal components, mutation status, birth cohort, and country of enrollment.