Table 3. Mean percent density by quartiles of plasma IGF-1, IGFBP-3, and GH among premenopausal women in NHS and NHSII by categories of age and BMI.
| Q1 | Q2 | Q3 | Q4 | p-trend | p-het | |
|---|---|---|---|---|---|---|
| IGF-1 | ||||||
| Mean percent density: by age | ||||||
| N | 35 | 39 | 66 | 72 | ||
| Age: <45 yearsa | 45.3 | 45.8 | 43.6 | 45.9 | 0.91 | 0.92 |
| N | 161 | 156 | 130 | 124 | ||
| Age: 45+ yearsa | 36.8 | 39.3 | 37.9 | 36.4 | 0.79 | |
| Mean percent density: by BMI | ||||||
| N | 99 | 125 | 127 | 125 | ||
| BMI:<25 kg/m2a | 48.0 | 48.7 | 46.7 | 45.5 | 0.24 | 0.16 |
| N | 97 | 70 | 69 | 71 | ||
| BMI: 25+ kg/m2a | 26 | 28.7 | 28.2 | 28.4 | 0.44 | |
| IGFBP-3 | ||||||
| Mean percent density: by age | ||||||
| N | 45 | 56 | 54 | 57 | ||
| Age: <45 yearsa | 46.6 | 46.2 | 43.8 | 45.9 | 0.67 | 0.98 |
| N | 151 | 139 | 142 | 139 | ||
| Age: 45+ yearsa | 38.0 | 39.0 | 35.4 | 37.9 | 0.65 | |
| Mean percent density: by BMI | ||||||
| N | 124 | 118 | 121 | 113 | ||
| BMI:<25 kg/m2a | 48.6 | 47.3 | 45.8 | 46.8 | 0.39 | 0.25 |
| N | 72 | 77 | 75 | 83 | ||
| BMI: 25+ kg/m2a | 26.6 | 30.5 | 26.2 | 27.3 | 0.90 | |
| GH | ||||||
| Mean percent density: by age | ||||||
| N | 78 | 32 | 28 | 37 | ||
| Age: <45 yearsa | 44.9 | 41.1 | 47.9 | 44.4 | 0.89 | 0.82 |
| N | 68 | 45 | 47 | 39 | ||
| Age: 45+ yearsa | 43.5 | 36.7 | 39.4 | 42.2 | 0.76 | |
| Mean percent density: by BMI | ||||||
| N | 88 | 52 | 46 | 47 | ||
| BMI:<25 kg/m2a | 50.0 | 48.8 | 52.9 | 51.8 | 0.51 | 0.21 |
| N | 58 | 25 | 29 | 29 | ||
| BMI: 25+ kg/m2a | 33.8 | 19.7 | 28.5 | 29.4 | 0.85 |
Quartile/category cutpoints: IGF-1 ng/ml (156.6, 193.8, 236.5), IGFBP-3 ng/ml (3364.8, 3797.2, 4208.8), IGF-1:IGFBP-3 molar ratio (0.16, 0.19, 0.22), GH ng/ml (batch 1: <0.14, 0.14–0.57, 0.50–2.14, 2.14+; batch 2:<0.18, 0.18–0.45, 0.45–1.30, 1.30+)
Adjusted for age at mammography (continuous), month of blood draw (continuous), fasting status (<8 h or unknown, ≥8 h since last meal), time of day of blood collection (12 am–5:59 am, 6:00 am–7:59 am, 8:00 am–11:59 pm), cohort, history of bbd (yes, no), family history of breast cancer (yes, no), age at menarche (continuous), parity and age at first birth (nulliparous, 1–2 children age at first birth <25 years, 1–2 children age at first birth 25–29 years, 1–2 children age at first birth ≥30 years, 3+ children age at first birth <25 years, 3+ children age at first birth 25+ years), alcohol consumption (0, <5, 5– <15, ≥15 g/day, missing), smoking status (never, past, current), BMI (continuous), also adjusts for IGFBP-3 (quartiles) in the IGF-1 model and for IGF-1 (quartiles) in the IGFBP-3 model