Table 2.
Risk (hazard ratios) of breast cancer associated with circulating insulin-like growth factor-1 (IGF-1) concentrations in the UK Biobank
| IGF-1 at baseline (nmol/l) | N Cases/participants | HR (95% CI) |
HR (95% CI) |
HR (95% CI) |
|---|---|---|---|---|
| Model0 | Model1 | Model2 | ||
| Fifths | ||||
| 1 (<16.4) | 836/40 428 | 1 (reference) | 1 (reference) | 1 (reference) |
| 2 (16.4 to <19.5) | 818/40 438 | 1.00 (0.91–1.10) | 1.01 (0.92–1.11) | 1.01 (0.91–1.11) |
| 3 (19.5 to <22.3) | 911/40 328 | 1.15 (1.05–1.27) | 1.16 (1.06–1.28) | 1.15 (1.05–1.27) |
| 4 (22.3 to <25.6) | 895/40 369 | 1.16 (1.06–1.28) | 1.18 (1.07–1.30) | 1.17 (1.06–1.29) |
| 5 (≥25.6) | 900/40 340 | 1.23 (1.12–1.36) | 1.25 (1.13–1.38) | 1.24 (1.12–1.37) |
| Ptrend | <0.0001 | <0.0001 | <0.0001 | |
| Per 5 nmol/l increment | 4360/206 263 | 1.08 (1.05–1.11) | 1.08 (1.05–1.11) | 1.08 (1.05–1.11) |
| Per 5 nmol/l increment (adjusted)a | 4360/206 263 | 1.11 (1.07–1.15) | 1.11 (1.07–1.15) | 1.11 (1.07–1.16) |
Model0: minimally adjusted model using age as the underlying time variable and stratified by Townsend deprivation index (fifths), region of the recruitment assessment centre, and age at recruitment (5-year categories).
Model1: multivariable Cox regression model using age as the underlying time variable and stratified by Townsend deprivation index (fifths), region of the recruitment assessment centre, and age at recruitment (5-year categories). Models adjusted for total physical activity (<10, 10 to <20, 20 to <40, 40 to <60, ≥60 metabolic equivalent hours per week, unknown); height (per 10 cm); alcohol consumption frequency (never, special occasions only, one to three times per month, one to two times per week, three to four times per week, daily/almost daily, unknown); smoking status and intensity (never, former, current <15 per day, current ≥15 per day, current intensity unknown, unknown); educational level (CSEs/O-levels/GCSEs or equivalent, NVQ/HND/HNC/A-levels/AS-levels or equivalent, other professional qualifications, college/university degree, none of the above, unknown); ever use of hormone replacement therapy (no, yes, unknown); parity, age at first birth (nulliparous; 1–2, <25 years; 1–2, 25–30 years; 1–2, ≥30 years; 1–2, unknown; ≥3, <25 years; ≥3, 25–30 years; ≥3, ≥30 years; ≥3, unknown; unknown); and the interaction between menopausal status and body mass index (kg/m2).
Model2: Model1 plus additional adjustment for circulating concentrations (fifths, missing/unknown) of C-reactive protein (CRP; mg/l), glycated haemoglobin (HbA1c; mmol/mol), testosterone (nmol/l), and sex hormone binding globulin (SHBG; nmol/l).
CI, confidence interval; HR, hazard ratio; SD, standard deviation.
HRs per SD increment were additionally corrected for regression dilution using a regression dilution ratio (0.74) obtained from the subsample of women with repeat IGF-1 measurements.