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.