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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)     
    Low 0-0.75 41/50 1.0 1.0 
    Medium 0.76-1.49 30/51 0.44 (0.21-0.93) 0.43 (0.20-0.96) 
    High 1.50-8.8 26/52 0.42 (0.20-0.90) 0.40 (0.18-0.86) 
    P for highest vs lowest tertile of intake   0.02 0.07 
    Ptrend§   0.02 0.03 
Adolescence (subject interviewed)     
    Low 0-0.50 215/315 1.0 1.0 
    Medium 0.51-1.9 186/303 0.92 (0.69-1.22) 0.95 (0.71-1.27) 
    High 2.0-8.9 175/324 0.77 (0.57-1.04) 0.80 (0.59-1.08) 
    P for highest vs lowest tertile of intake   0.09 0.15 
    Ptrend§   0.08 0.12 
Adulthood (subject interviewed)     
    Low 0-0.43 205/298 1.0 1.0 
    Medium 0.44-1.10 222/339 1.00 (0.77-1.30) 0.99 (0.76-1.30) 
    High 1.11-12.0 164/325 0.71 (0.53-0.95) 0.76 (0.56-1.02) 
    P for highest vs lowest tertile of intake   0.03 0.02 
    Ptrend§   0.01 0.04 
Soy intake*Range (times/wk)Cases/controlsRR (95% CI) simplified modelRR (95% CI) fully adjusted model
Childhood (mother interviewed)     
    Low 0-0.75 41/50 1.0 1.0 
    Medium 0.76-1.49 30/51 0.44 (0.21-0.93) 0.43 (0.20-0.96) 
    High 1.50-8.8 26/52 0.42 (0.20-0.90) 0.40 (0.18-0.86) 
    P for highest vs lowest tertile of intake   0.02 0.07 
    Ptrend§   0.02 0.03 
Adolescence (subject interviewed)     
    Low 0-0.50 215/315 1.0 1.0 
    Medium 0.51-1.9 186/303 0.92 (0.69-1.22) 0.95 (0.71-1.27) 
    High 2.0-8.9 175/324 0.77 (0.57-1.04) 0.80 (0.59-1.08) 
    P for highest vs lowest tertile of intake   0.09 0.15 
    Ptrend§   0.08 0.12 
Adulthood (subject interviewed)     
    Low 0-0.43 205/298 1.0 1.0 
    Medium 0.44-1.10 222/339 1.00 (0.77-1.30) 0.99 (0.76-1.30) 
    High 1.11-12.0 164/325 0.71 (0.53-0.95) 0.76 (0.56-1.02) 
    P for highest vs lowest tertile of intake   0.03 0.02 
    Ptrend§   0.01 0.04 
*

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.

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