Figure 2

Covariance and correlation between ¹ H NMR one dimensional urine spectra, and population characteristics. The color code (R²) corresponds to the correlation coefficients of the variables with each of the characteristics: A, ln(U-Cd); B, age; C, sex; D, ln(U-NAG); and E, smoking status. N = 127. α - The direction and magnitude of the signals relate to the covariation of the metabolites with sex in the model, that is, female (positive) and male (negative). β - Smoking status was classified into two classes. 1 = never smoked (negative), 2 = current smoker (positive). 3-HV, 3-hydroxyisovalerate; DMG, dimethylglycine; 4-DEA, 4-deoxyerythronic acid. Spectra that exhibited signs of bacterial contamination, analgesics or ethanol were excluded from these analyses [See additional file 1 Table S2].