Associations between urinary soy isoflavonoids and two inflammatory markers in adults in the United States in 2005-2008

The aim of this study was to determine the association between urinary isoflavonoid (genistein, daidzein, and the daidzein metabolites O-desmethylangolensin (O-DMA) and equol) excretion and markers of inflammation in adults in the United States in National Health and Nutrition Examination Survey (NHANES) 2005-2008. The NHANES is a cross-sectional study conducted by the National Center for Health Statistics to study the health and nutritional status of people living in the United States. The analysis included 1,683 participants from study years 2005-2008 for whom urinary isoflavonoids were measured and who met inclusion criteria. Urinary isoflavonoids were measured by HPLC-APPI-MS/MS. Serum C-reactive protein (CRP) was measured by latex-based nephelometry. White blood cell (WBC) count was measured by Coulter counting. Multivariable linear regression was used to calculate the geometric mean values of the markers, and multivariable logistic regression was used to estimate the odds of high CRP (a parts per thousand yen3 mg/L) and of high WBC count (a parts per thousand yen7,900/mu L) by quartile of urinary isoflavonoid (nmol/mg creatinine). The highest quartile of genistein (OR = 0.62; 95 % CI 0.39-0.99) was associated with significantly decreased odds of high CRP compared with the lowest quartile. The sum of daidzein and its metabolites was significantly inversely associated with serum CRP concentration (p-trend = 0.017). Equol was inversely associated with WBC count (p-trend < 0.0001). O-DMA was the only isoflavonoid whose excretion was significantly associated with a decrease in both CRP (p-trend = 0.024) and WBC count (p-trend < 0.0001). Though no clear pattern emerged, higher excretion of certain soy isoflavonoids was associated with decreased CRP concentration and WBC counts, suggesting a possible inverse association between soy intake and inflammation.