Table 2.

RR of breast cancer and 95% CI by tertiles of soy intake during childhood, adolescence, and adulthood

Soy intake*Range (times/wk)Cases/controlsRR (95% CI) simplified modelRR (95% CI) fully adjusted model
Childhood (mother interviewed)
    Low0-0.7541/501.01.0
    Medium0.76-1.4930/510.44 (0.21-0.93)0.43 (0.20-0.96)
    High1.50-8.826/520.42 (0.20-0.90)0.40 (0.18-0.86)
    P for highest vs lowest tertile of intake0.020.07
    Ptrend§0.020.03
Adolescence (subject interviewed)
    Low0-0.50215/3151.01.0
    Medium0.51-1.9186/3030.92 (0.69-1.22)0.95 (0.71-1.27)
    High2.0-8.9175/3240.77 (0.57-1.04)0.80 (0.59-1.08)
    P for highest vs lowest tertile of intake0.090.15
    Ptrend§0.080.12
Adulthood (subject interviewed)
    Low0-0.43205/2981.01.0
    Medium0.44-1.10222/3391.00 (0.77-1.30)0.99 (0.76-1.30)
    High1.11-12.0164/3250.71 (0.53-0.95)0.76 (0.56-1.02)
    P for highest vs lowest tertile of intake0.030.02
    Ptrend§0.010.04
  • * Soy intake was stratified as tertiles based on the frequency distribution of intake among controls in each period, and the low tertile was used as the reference category.

  • The simplified model is adjusted for study design variables [age at diagnosis (20-39, 40-44, 45-49, ≥50 y), ethnicity (Chinese, Japanese, Filipino), and study center (Hawaii, Los Angeles, San Francisco-Oakland)] and parity/age at first live birth (nulliparous/never pregnant, 1-2 live births/age at first birth ≤20 y, ≥3 live births/age at first live birth ≤20 y, 1-2 live births/age at first live birth ≥21 y, ≥3 live births/age at first live birth ≥21 y, missing).

  • The fully adjusted model includes study design variables and known breast cancer risk factors: parity/age at first live birth (stratified into six categories as described above), menopausal status at diagnosis (premenopausal, postmenopausal, missing/other), age at menarche (<13 y, ≥13 y, missing/other), family history of breast cancer (yes, no), and personal history of benign breast disease (yes, no, missing).

  • § P values for trend were calculated by assigning to each tertile the median soy intake for all subjects in the tertile.