Table 2.

Means and correlations of C-peptide levels with breast density (n = 1,499)

Type of adjustmentMeans of breast density* (%) by quartiles of C-peptide (ng/mL)
Spearman correlation coefficients (P)
Quartile 1 (≤1.324)Quartile 2 (1.325-2.143)Quartile 3 (2.144-3.497)Quartile 4 (>3.497)
Covariates 135.430.027.623.2−0.210 (<0.0001)
Covariates 2§34.629.127.623.2−0.198 (<0.0001)
Covariates 1 + BMI (kg/m2)28.728.127.627.0−0.057 (0.03)
Covariates 2 + BMI (kg/m2)28.527.627.626.9−0.054 (0.04)
Covariates 1 + WHR30.928.728.226.0−0.086 (0.0008)
Covariates 2 + WHR30.628.028.225.9−0.081 (0.002)
Covariates 1 + BMI (kg/m2) + WHR27.727.827.827.8−0.022 (0.41)
Covariates 2 + BMI (kg/m2) + WHR27.627.327.927.6−0.022 (0.41)
  • * Means of breast density are presented as back-transformed values.

  • Spearman correlation between continuous variables. Adjusted correlations are partial Spearman coefficients.

  • Means and correlations are adjusted for age (y) and time since last meal (≤2, >2-3, >3-4, >4-5, >5 h).

  • § Means and correlations are adjusted for age (y) and time since last meal (≤2, >2-3, >3-4, >4-5, >5 h), alcohol (drinks/wk) and total energy (kcal/day) intakes in the past year, menopausal status (premenopausal or postmenopausal), age at menarche (y), age at first full-term pregnancy (y), lactation (y), number of full-term pregnancies, number of personal breast biopsies, duration of past use of oral contraceptive and of hormone replacement therapy (y), family history of breast cancer in first-degree relative (yes/no), physical activity (METs h/wk), education (primary or less, secondary, college, or university diploma), and smoking status (never, former, or current smoker). Analysis are restricted to n = 1,474 due to missing values for some breast cancer risk factors among participants.