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Table 2 Characteristics of study subjects (N = 741)

From: Polymorphisms in genes involved in the estrogen pathway and mammographic density

Characteristic Mean SD
Age at mammography (years) 46.8 4.6
Body mass index (kg/m2) 25.2 4.6
Waist-to-hip ratio 0.8 0.1
Height (cm) 160.5 5.8
Age at menarche (years) 12.7 1.6
Age at first pregnancy (years) a (n = 563) 26.0 3.7
Number of live births a (n = 563) 2.1 0.8
Alcohol intake (drinks/wk) (n = 738) 3.4 3.8
Total energy intake (Kcal/day) (n = 736) 1906.0 514.9
Physical activity (MET-h/wk) (n = 740) 27.1 22.2
Percent density (%) 42.3 24.3
Absolute density (cm²) 47.1 28.7
  %  
Parity (parous) 76.0  
Lactation (yes) a (n = 563) 62.0  
Personal history of breast biopsies (yes) 14.2  
Past hormonal derivative use (yes) (n = 740) b 92.4  
First degree relative with breast cancer (yes) 36.8  
Education (college or university degree) 62.0  
Smoking status (never) 45.1  
  1. a Among parous women
  2. b Past oral contraceptive (92.2%) and hormone replacement therapy (6.1%) uses