Table 2. Mean percent density by quartiles of plasma IGF-1, IGFBP-3, IGF-1:IGFBP-3 ratio, and growth hormone among premenopausal women in the NHS and NHSII.

	Mean percent density				p-trend
	Q1	Q2	Q3	Q4
IGF-1
N	196	195	196	196
Model 1a	38.1	42.1	39.5	38.7	0.94
Model 2b	39.2	41.1	39.1	39.2	0.81
IGFBP-3
N	196	195	196	196
Model 1a	40.9	40.3	39.2	37.8	0.11
Model 2b	40.5	40.5	38.3	39.2	0.33
IGF-1/IGFBP-3 ratio
N	195	197	195	196
Model 1a	37.8	40.3	40.8	39.6	0.36
Model 2b	39.8	40.2	39.6	38.8	0.53
Growth hormone (NHSII only)
N	146	77	75	76
Model 1a	42.5	39.5	43.7	44.6	0.31
Model 2b	43.9	38.9	43.2	42.8	0.90

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, 0.57–2.14, 2.14+; batch 2:<0.18, 0.18–0.45, 0.45–1.30, 1.30+)

^aModel 1: 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), and cohort (except for growth hormone)

^bIncludes covariates in Model 1 and history of bbd (yes/no), family history of breast cancer (yes/no), age at menarche (<12, 12, 13, 14+), 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), and BMI (continuous), also adjusts for IGFBP-3 (quartiles) in the IGF-1 model and for IGF-1 (quartiles) in the IGFBP-3 model