The relationship between phytoestrogens and speed of processing.

Objective: This study examined the cross-sectional association between phytoestrogens and speed of processing. We hypothesized that higher levels of phytoestrogens would be related to better cognitive performance among older women.

Methods: Participants were from the National Health and Nutrition Examination Survey and consisted of 200 older women (M = 74.4 y). Stepwise regressions examined indicators of speed of processing, measured by the Digit Symbol Substitution Test. Isoflavones, lignans, and individual phytoestrogens were added to the regression after including covariates of age, education, race, smoking, and creatinine. Isoflavones were further broken into quartiles among the sample to further evaluate the nature of the curvilinear association.

Results: Results showed a relationship between cognition and lignans, explaining 3.8% of the variance after including the covariates, indicating fewer lignans were associated with better speed of processing (P < 0.001). A significant curvilinear relationship with isoflavones explained 1.3% additional variance (P < 0.001). The moderate-high, low-moderate, and the lowest quartile of isoflavones were associated with better cognition, whereas the highest amount was associated with worse speed of processing. Among the individual phytoestrogens, only enterodiol accounted for 4.4% additional variance after taking into account covariates and indicated a negative association with cognition (P = 0.03).

Conclusions: Results suggest that moderate levels of isoflavones, but not lignans, may be associated with better speed of processing. Caution must remain for high isoflavone amounts due to the negative association with cognition. Given the results, phytoestrogens have the potential to be an intervention target for older females' cognition. To become a viable intervention, further research is needed.