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Table 1 Mean percentage of breast density by descriptive characteristics (n = 396)

From: Genetic determinants of mammographic density

Characteristic n (%) Mean % density P §
Race*
   African-American 152 (38) 34.8  
   Whites 244 (68) 34.8 0.98
Menopausal status/ HRT use**,†
   Premenopausal 176 (44) 35.4  
   Postmenopausal    
Never used or past user of HRT 67 (17) 30.4  
Current user of ERT 53 (13) 39.3  
Current user of EPRT 51 (13) 39.8 0.08
Age at mammogram (years)
   ≤ 40 91 (23) 45.6  
   41–45 84 (21) 41.2  
   46–50 41 (10) 38.3  
   51–55 74 (19) 34.4  
   56–60 69 (17) 28.3  
   >60 37 (9) 28.9 <0.0001
Body mass index (kg/m2)**
   <22 114 (29) 49.8  
   22–24.9 107 (27) 38.3  
   25–29.9 111 (28) 29.2  
   ≥ 30 64 (16) 21.8 <0.0001
Parity**
   0 83 (21) 45.1  
   1–2 175 (44) 38.0  
   3+ 138 (35) 29.1 <0.0001
Age at first birth (years)**
   <25 191(61) 30.9  
   25–30 69 (22) 35.1  
   ≥ 30 53 (17) 43.8 0.0004
Age at menarche (years)**
   <12 106 (27) 32.6  
   12 105 (27) 36.5  
   13 97 (24) 34.7  
   >13 88 (22) 41.3 0.04
First-degree family history of breast cancer**,‡
   No 256 (65) 35.0  
   Yes 120 (30) 39.3 0.12
  1. *Adjusted for age and body mass index. **Adjusted for age. n = 49 missing menopausal/ hormone replacement therapy (HRT) status. n = 20 missing family history information. §Analysis of covariance. EPRT, estrogen plus progestin replacement therapy; ERT, estrogen replacement therapy.