Table 3.

RR and 95% CI of breast cancer by quartiles of circulating insulin and c-peptide levels

Plasma hormoneCases/controlsQ1Q2Q3Q4Ptrend
Insulin
    Cut points (μU/mL)≤6.156.16-7.507.51-9.91≥9.92
    All (simple*)208/4091.00.7 (0.4-1.1)0.8 (0.5-1.3)0.7 (0.4-1.1)0.20
    All (multivariate)208/4091.00.7 (0.4-1.2)0.7 (0.4-1.3)0.5 (0.3-1.0)0.06
    Premenopausal148/2891.00.6 (0.3-1.1)0.6 (0.3-1.0)0.5 (0.3-1.0)0.08
    Invasive148/4091.00.7 (0.4-1.2)0.8 (0.4-1.4)0.6 (0.3-1.2)0.25
    ER+/PR+99/4091.00.7 (0.4-1.3)0.8 (0.4-1.5)0.5 (0.2-1.1)0.11
c-Peptide
    Cut points (ng/mL)≤1.031.04-1.491.50-2.28≥2.29
    All (simple*)316/6291.01.3 (0.9-2.0)1.1 (0.7-1.6)1.0 (0.7-1.6)0.73
    All (multivariate)316/6291.01.4 (1.0-2.2)1.1 (0.7-1.7)1.1 (0.7-1.7)0.79
    Premenopausal238/4721.01.4 (0.9-2.2)1.2 (0.7-2.0)1.2 (0.7-2.1)0.86
    Invasive218/6291.01.4 (0.9-2.2)1.0 (0.6-1.7)1.4 (0.8-2.4)0.45
    ER+/PR+144/6291.02.0 (1.1-3.4)1.3 (0.7-2.4)2.0 (1.0-3.9)0.15
  • Abbreviations: ER, estrogen receptor; PR, progesterone receptor.

  • * Conditional logistic regression.

  • Conditional logistic regression, adjusting for BMI at age 18 (<21, 21 to <23, ≥23 kg/m2), BMI at blood (continuous), age at menarche (<12, 12, 13, ≥14 years), parity/age at first birth (nulliparous, age at first birth <25 years/1-4 children, age at first birth 25-29 years/1-4 children, age at first birth ≥30 years/1-4 children, age at first birth <25 years/≥5 children, age at first birth ≥25 years/≥5 children), family history of breast cancer (yes, no), and history of benign breast disease (yes, no).

  • Unconditional logistic regression, adjusting for matching factors [days from luteal draw to next menstrual cycle (0-5, 6-7, 8-9, 10-28 days), age at blood collection (continuous), date of blood collection (continuous), fasting at blood collection (yes, no), time of blood collection (1-4 a.m., 5-6 a.m., 7 a.m. to 12 p.m., continuous), race/ethnicity (Caucasian, other), and menopausal status at blood collection (premenopausal, postmenopausal, unknown)] in addition to covariates above.