Characteristic | Figure at age 10 years | ||||
---|---|---|---|---|---|
 | 1 | 2 | 3 | 4 | ≥ 5 |
Number participants (%) | 20,554 (18.8) | 33,512 (30.7) | 24,666 (22.6) | 17,274 (15.8) | 13,261 (12.1) |
Mean | |||||
   Age (years) | 34.6 | 34.0 | 34.1 | 34.3 | 34.7 |
   Total caloric intake in high school (kilocalories)a | 2737 | 2746 | 2745 | 2746 | 2781 |
   Animal fat intake in high school (% energy)a | 26.0 | 25.7 | 25.8 | 25.9 | 26.2 |
   Vegetable fat intake in high school (% energy)a | 14.4 | 14.7 | 14.8 | 15.0 | 15.0 |
   Age at menarche (years) | 12.8 | 12.6 | 12.3 | 12.1 | 12.0 |
   Height (inches) | 64.9 | 64.9 | 64.8 | 64.8 | 65.0 |
   BMI at age 18 years (kg/m2) | 19.3 | 20.2 | 21.5 | 22.9 | 24.3 |
   Current BMI (kg/m2) | 22.0 | 22.7 | 24.4 | 26.1 | 27.1 |
   Age at first birth (years)b | 25.4 | 25.5 | 25.6 | 25.6 | 25.4 |
   Parityb | 2.1 | 2.1 | 2.1 | 2.1 | 2.0 |
Percentage | |||||
   Birthweight ≥ 8.5 lb | 8.3 | 9.4 | 11.7 | 12.9 | 13.7 |
   ≥ 3 years from menarche until regular menstrual cycles | 19.5 | 18.5 | 17.7 | 17.9 | 19.6 |
   Irregular menstrual cycles/no periods ages 18–22 years | 9.7 | 9.0 | 8.8 | 10.2 | 11.2 |
   Menstrual cycle length ≥ 40 days ages 18–22 years | 7.1 | 7.1 | 7.3 | 8.2 | 8.6 |
   Strenuous activity 10–12 months/year in high school | 28.7 | 28.0 | 26.2 | 21.4 | 17.6 |
   BMI at age 18 years ≥ 25 kg/m2 | 1.8 | 3.1 | 8.9 | 19.5 | 32.2 |
   Current BMI ≥ 30 kg/m2 | 3.0 | 4.9 | 11.2 | 20.2 | 24.6 |
   Nulliparous | 29.6 | 29.2 | 29.3 | 31.3 | 35.0 |
   Current oral contraceptive user | 13.8 | 14.0 | 12.6 | 12.7 | 11.6 |
   Current smoker | 13.1 | 11.5 | 12.3 | 14.2 | 18.6 |
   Alcohol consumption ≥ 10 g/day | 9.7 | 9.0 | 9.1 | 9.1 | 9.9 |
   First-degree family history of breast cancer | 5.9 | 6.0 | 5.7 | 5.9 | 6.3 |
   History of benign breast disease | 30.3 | 28.1 | 27.6 | 27.5 | 28.0 |