Phytoestrogen consumption and risk for cognitive decline and dementia: With consideration of thyroid status and other possible mediators

It is predicted that around 20% of the worlds population will be age 60 or above by 2050. Prevalence of cognitive decline and dementia is high in older adults and modifiable dietary factors may be able to reduce risk for these conditions. Phytoestrogens are bioactive plant chemicals found in soy, which have a similarity in structure to natural estradiol (the most abundant circulating estrogen). This structural likeness enables phytoestrogens to interact with estrogen receptors in the brain, potentially affecting cognition. However, findings in this domain are largely inconsistent, with approximately 50% of studies showing positive effects of phytoestrogens on cognition and the other half resulting in null/negative findings. This paper provides an updated review of the relationship between consumption of phytoestrogens and risk for cognitive decline and/or dementia. In particular, possible mediators were identified to explain discrepant findings and for consideration in future research. A case can be made for a link between phytoestrogen consumption, thyroid status and cognition in older age, although current findings in this area are very limited. Evidence suggests that inter-individual variants that can affect phytoestrogen bioavailability (and thus cognitive outcome) include age and ability to breakdown ingested phytoestrogens into their bioactive metabolites. Factors of the study design that must be taken into account are type of soy product, dosage, frequency of dietary intake and type of cognitive test used. Guidelines regarding optimal phytoestrogen dosage and frequency of intake are yet to be determined.

Tempereversed effects of ovariectomy on brain function in rats: Effects of age and type of soy product

BACKGROUD

The aims of this study were to analyze the differences in nutrient content and isoflavones in tempe flour and tofu flour, and to analyze the effect of tempe and tofu flour on cognitive function of female rats after ovariectomy.

METHOD

Seventy two (72) white female Sprague Dawley strain rats, aged 12 months were used for this study. Before the intervention 52 rats underwent ovariectomy (OVx) and they were grouped into 4 intervention groups: tempe flour (Tp), tofu flour (Tf), estradiol (E2), and casein as a control protein (Cs). The remaining 20 rats were classed as controls and had no ovariectomy (NO). Cognitive function was measured using a maze test. Oneway ANOVA with polynomial contrasts and post hoc LSD were used with a p-value<0.05 to indicate significance.

RESULTS

The content of nutrients (vitamin B6, vitamin B12, folic acid) and isoflavones (genistein) were all higher in tempe flour higher than in tofu flour. After 8 weeks, the Tp group had showed significantly increased cognitive function (P<0.05), while the Tf group, the E2 group and the Cs group also all had increased performance, but not significantly so (P>0.05). There was no change in scores in the NO group.

CONCLUSIONS

Intervention by tempe flour can increase cognitive function in female ovariectomized female rats. Further research should focus onother aspects of cognitive function and the content of amyloid plaques and neurotransmitter synthesis in the brain.