Table 1

Baseline distributions of breast cancer risk factors by quintiles of energy-adjusted glycemic load (GL) in the Women’s Health Study

Quintile of energy-adjusted GLP
1 (n = 7689)2 (n = 7689)3 (n = 7690)4 (n = 7689)5 (n = 7689)
GL (median)92106117127143
Overall GIa (mean within GL quintile)50 ± 352 ± 353 ± 354 ± 355 ± 3<0.0001b
Mean age (yr)53.5 ± 6.753.6 ± 6.853.9 ± 7.054.2 ± 7.154.4 ± 7.4<0.0001b
Postmenopausal at baseline (%)52.453.354.056.257.4<0.0001c
Mean BMIa26.7 ± 5.426.3 ± 5.026.1 ± 5.025.7 ± 4.825.2 ± 4.7<0.0001b
Current or past smoker (%)60.851.647.043.741.7<0.0001c
Alcohol use (%)<0.0001c
 Rarely/never32.940.243.148.559.1
 1–3 drinks/mo10.512.814.414.214.0
 1–6 drinks/wk34.035.333.931.823.6
 ≥1 drink/day22.611.88.55.43.2
Physical activity (mean kJ expended per wk)3493 ± 47733806 ± 48934104 ± 48844318 ± 53124555 ± 5510<0.0001b
Breast cancer in mother or sister at age <60 (%)6.06.06.06.26.00.96c
Hormone replacement therapy use (%)0.0012c
 Current use (at baseline)39.941.442.143.142.4
 Past use only10.410.39.69.910.9
 Never49.448.248.046.946.5
Age at menarche (%)0.33c
 ≤10 yr8.68.28.57.98.0
 11 yr16.816.416.316.015.3
 12 yr27.828.629.328.228.0
 13 yr29.228.828.129.029.2
 14 yr10.010.210.611.111.2
 ≥15 yr7.57.77.07.88.2
Oral contraceptive use (ever used for ≥2 mo)72.471.168.868.165.3<0.0001c
Age at first pregnancy lasting ≥6 months (%)<0.0001c
 Not applicable12.310.311.012.111.9
 <20 yr10.59.28.69.09.3
 20–24 yr44.445.245.143.342.2
 25–29 yr22.524.724.324.725.1
 ≥30 yr9.49.89.910.210.5
Pregnancies lasting ≥6 mo (%)0.0002c
 013.311.312.413.013.1
 19.49.08.88.49.5
 229.829.628.928.930.0
 323.425.524.424.423.0
 413.413.913.913.913.6
 ≥510.210.211.111.010.5
History of diabetes mellitus (%)3.82.62.52.11.7<0.0001c
History of hypertension (%)27.826.125.425.124.5<0.0001c
History of hypercholesterolemia (%)27.628.728.729.033.3<0.0001c
Screening mammogram reported at baseline (%)91.092.393.093.392.1<0.0001c
  • a GI, glycemic index; BMI, body mass index.

  • b P for a test for linear trend.

  • c P for a test of independence.