Habitual dietary isoflavone intake is associated with decreased C-reactive protein concentrations among healthy premenopausal women.

Isoflavones have been associated with lower cardiovascular disease risk, but existing research focused on very high isoflavone intakes, as seen in Asian populations, as well as on risk factor reductions primarily in postmenopausal women. We investigated whether habitual low isoflavone intake among premenopausal women was associated with serum C-reactive protein (CRP) concentration, a commonly used biomarker associated with prediction of cardiovascular disease risk in healthy women. Between 2005 and 2007, 259 healthy, regularly menstruating women were enrolled in the BioCycle Study, and followed for up to 2 menstrual cycles. CRP was measured in serum at up to 16 clinic visits, timed to phases of the women's menstrual cycle. Diet was assessed up to 4 times per cycle by using 24-h recalls. Marginal structural models with inverse probability of exposure weights estimated the association between CRP and quartiles of isoflavone intake adjusted for age, race, BMI, cycle phase, total energy intake, total fiber, total whole grains, and phase-specific hormone concentrations including estradiol, progesterone, luteinizing hormone, and follicle-stimulating hormone. Compared with the lowest quartile of total isoflavone intake, women in the highest quartile had, on average, 27% lower serum CRP concentrations (95% CI: -35, -21%). Our results suggest that dietary isoflavone intakes at levels characteristic of the U.S. population are associated with decreased serum CRP concentrations, a factor associated with beneficial effects on inflammation, and subsequently may have the potential to improve health status among young women.