Associations between urine excretion of isoflavonoids and cognition in postmenopausal women in the Women's Isoflavone Soy Health clinical trial

Genistein Prevents Single Prolonged Stress-Induced Cognitive Impairment in a Post-Traumatic Stress Disorder Rat Model via Activation of the Serotonergic System

Post-traumatic stress disorder (PTSD) is a stress-associated mental disorder characterized by an imbalance of neurotransmitters in response to traumatic events or fear. Genistein (GEN), a natural isoflavone, has been shown to exhibit neuroprotective effects. Here, we used the Morris water maze (MWM) and object recognition task (ORT) tests to examine the effects of GEN on cognitive impairment in rats after exposure to single prolonged stress (SPS), and its interaction with the serotonergic system. After exposure to SPS, male rats received GEN (2, 4, and 10 mg/kg, i.p.) for 14 days. Daily GEN administration significantly improved cognitive function in the ORT and MWM tests. GEN treatment also inhibited SPS-induced decreases in serotonin (5-HT) levels in the medial prefrontal cortex and hippocampus. These increased 5-HT concentrations in response to GEN treatment could be partially attributed to the ratio of 5-hydroxyindoleacetic acid/5-HT in the hippocampus. Our findings suggest that GEN significantly attenuates SPS-induced memory deficits in rats and may represent an effective therapeutic option for the treatment of PTSD.

Nutritional Intervention as a Preventive Approach for Cognitive-Related Outcomes in Cognitively Healthy Older Adults: A Systematic Review

The link diet-cognitive function/dementia has been largely investigated in observational studies; however, there was a lack of evidence from randomized clinical trials (RCTs) on the prevention of late-life cognitive disorders though dietary intervention in cognitively healthy older adults. In the present article, we systematically reviewed RCTs published in the last four years (2014-2017) exploring nutritional intervention efficacy in preventing the onset of late-life cognitive disorders and dementia in cognitively healthy subjects aged 60 years and older using different levels of investigation (i.e., dietary pattern changes/medical food/nutraceutical supplementation/multidomain approach and dietary macro- and micronutrient approaches) as well as possible underlying mechanisms of nutritional prevention. From the 35 included RCTs, there was moderate evidence that intervention through dietary pattern changes, medical food/nutraceutical supplementation, and multidomain approach improved specific cognitive domains or cognitive-related blood biomarkers. There was high evidence that protein supplementation improved specific cognitive domains or functional status in prefrail older adults without effect on cognitive function. For fatty acid supplementation, mainly long-chain polyunsaturated fatty acids, there was emerging evidence suggesting an impact of this approach in improving specific cognitive domains, magnetic resonance imaging (MRI) findings, and/or cognitive-related biomarkers also in selected subgroups of older subjects, although some results were conflicting. There was convincing evidence of an impact of non-flavonoid polyphenol and flavonoid supplementations in improving specific cognitive domains and/or MRI findings. Finally, there was only low evidence suggesting efficacy of intervention with homocysteine-related and antioxidant vitamins in improving cognitive functions, dementia incidence, or cognitive-related biomarkers in cognitively healthy older subjects.

Low dietary soy isoflavonoids increase hippocampal spine synapse density in ovariectomized rats

High dietary intake of plant estrogens (phytoestrogens) can affect brain structure and function. The effects of phytoestrogen intake within the range of normal animal and human dietary consumption, however, remain uncertain. The aim of the present study was to determine the effects of the isoflavonoids present in a standard low phytoestrogen laboratory rat chow on spine synapse density in the stratum radiatum of area CA1 of the hippocampus. Weanling rats (22days old) were fed either standard chow (Teklad 2018), a nutritionally comparable diet without soy (Teklad 2016) or a custom diet containing Teklad 2016 supplemented with the principal soy isoflavonoids, daidzein and genistein, for 40days. Rats were ovariectomized at 54days of age. Eight days later, spine synapse density on the apical dendrites of hippocampal pyramidal neurons in the stratum radiatum of area CA1 was measured by electron microscopic stereological analysis. Animals maintained on Teklad 2016 exhibited an approximately 60% lower CA1 spine synapse density than animals consuming Teklad 2018. Replacing genistein and daidzein in Teklad 2016 returned synapse density to levels indistinguishable from those in animals on Teklad 2018. These results indicate that the isoflavonoids in a standard laboratory rat diet exert significant effects on spine synapse density in the CA1 region of the hippocampus. Since changes in spine synapse density in this region of the hippocampus have been linked to cognitive performance and mood state, these data suggest that even relatively low daily consumption of soy phytoestrogens may be sufficient to influence hippocampal function.

Soy and Health Update: Evaluation of the Clinical and Epidemiologic Literature

Soyfoods have long been recognized as sources of high-quality protein and healthful fat, but over the past 25 years these foods have been rigorously investigated for their role in chronic disease prevention and treatment. There is evidence, for example, that they reduce risk of coronary heart disease and breast and prostate cancer. In addition, soy alleviates hot flashes and may favorably affect renal function, alleviate depressive symptoms and improve skin health. Much of the focus on soyfoods is because they are uniquely-rich sources of isoflavones. Isoflavones are classified as both phytoestrogens and selective estrogen receptor modulators. Despite the many proposed benefits, the presence of isoflavones has led to concerns that soy may exert untoward effects in some individuals. However, these concerns are based primarily on animal studies, whereas the human research supports the safety and benefits of soyfoods. In support of safety is the recent conclusion of the European Food Safety Authority that isoflavones do not adversely affect the breast, thyroid or uterus of postmenopausal women. This review covers each of the major research areas involving soy focusing primarily on the clinical and epidemiologic research. Background information on Asian soy intake, isoflavones, and nutrient content is also provided.

Cognitive Effects of Soy Isoflavones in Patients with Alzheimer's Disease

BACKGROUND

In a previous trial, treatment with soy isoflavones was associated with improved nonverbal memory, construction abilities, verbal fluency, and speeded dexterity compared to treatment with placebo in cognitively healthy older adults.

OBJECTIVE

The current trial aimed to examine the potential cognitive benefits of soy isoflavones in patients with Alzheimer's disease.

METHODS

Sixty-five men and women over the age of 60 were treated with 100 mg/day soy isoflavones, or matching placebo capsules for six months. APOE genotype was determined for all participants. Cognitive outcomes and plasma isoflavone levels were measured at baseline, and at two additional time points: three and six months after baseline.

RESULTS

Of the sixty-five participants enrolled, thirty-four (52.3% ) were women, and 31 (47.7% ) were APOEɛ4 positive. Average age was 76.3 (SD = 7.2) years. Fifty-nine (90.8% ) subjects completed all study visits. Plasma isoflavone levels increased in subjects treated with soy isoflavones compared to baseline and to placebo, although intersubject variability in plasma levels was large. No significant differences in treatment effects for cognition emerged between treatment groups or genders. Exploratory analyses of associations between changes in cognition and plasma isoflavone levels revealed an association between equol levels, and speeded dexterity and verbal fluency.

CONCLUSIONS

Six months of 100 mg/day treatment with soy isoflavones did not benefit cognition in older men and women with Alzheimer's disease. However, our results suggest the need to examine the role of isoflavone metabolism, i.e., the ability to effectively metabolize soy isoflavones by converting daidzen to equol when attempting to fully clarify the cognitive effects of isoflavones.

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.

Beneficial effects of soy supplementation on postmenopausal atherosclerosis are dependent on pretreatment stage of plaque progression

OBJECTIVE

The objective of this study was to use a well-established monkey model of atherosclerosis to determine how life stage and preexisting atherosclerosis influence the effectiveness of high-isoflavone soy diet in inhibiting progression of atherosclerosis.

METHODS

For 34 months, premenopausal monkeys were fed an atherogenic diet, with protein derived primarily from either animal sources (casein-lactalbumin [CL], n = 37) or high-isoflavone soy beans (Soy, n = 34). Animals were ovariectomized and randomized to groups fed the same diet (CL-CL, n = 20; Soy-Soy, n = 17) or an alternate diet (CL-Soy, n = 17; Soy-CL, n = 17) for an additional 34 months. At ovariectomy, the left common iliac artery was removed to determine the amount of premenopausal atherosclerosis. At necropsy, the right common iliac artery and coronary arteries were collected, and atherosclerosis extent was quantified. CL-CL condition was considered "control."

RESULTS

Modeling Asian women who remain in Asia, monkeys fed soy protein both premenopausally and postmenopausally had a markedly reduced extent of coronary artery atherosclerosis relative to CL controls (P = 0.008). The subset of animals that modeled Asian women who migrate to a Western country (consuming soy premenopausally and CL postmenopausally) had increased progression of postmenopausal iliac artery atherosclerosis (P = 0.003) and was not protected against the development of coronary artery atherosclerosis relative to controls. Relevant to the administration of soy diets to postmenopausal Western women, monkeys fed CL premenopausally and switched to soy postmenopausally derived atheroprotective benefits only if they began the postmenopausal treatment period with relatively small (below the median) plaques. Relative to controls, this group (with small plaques at ovariectomy) had reduced progression of iliac atherosclerosis (P = 0.038) and smaller coronary artery plaques (P = 0.0001) that were less complicated (P = 0.05) relative to controls.

CONCLUSIONS

The results suggest that significant atheroprotective benefits of dietary soy are derived from treatment that begins premenopausally and continues postmenopausally or from treatment that is started during early postmenopause (when plaques are still small).

Individually modifiable risk factors to ameliorate cognitive aging: a systematic review and meta-analysis

A number of health and lifestyle factors are thought to contribute to cognitive decline associated with age but cannot be easily modified by the individual patient. We identified 12 individually modifiable interventions that can be implemented during midlife or later with the potential to ameliorate cognitive aging. For ten of these, we used PubMed databases for a systematic review of long-duration (at least 6 months), randomized, controlled trials in midlife and older adults without dementia or mild cognitive impairment with objective measures of neuropsychological performance. Using network meta-analysis, we performed a quantitative synthesis for global cognition (primary outcome) and episodic memory (secondary outcome). Of 1038 publications identified by our search strategy, 24 eligible trials were included in the network meta-analysis. Results suggested that the Mediterranean diet supplemented by olive oil and tai chi exercise may improve global cognition, and the Mediterranean diet plus olive oil and soy isoflavone supplements may improve memory. Effect sizes were no more than small (standardized mean differences 0.11-0.22). Cognitive training may have cognitive benefit as well. Most individually modifiable risk factors have not yet been adequately studied. We conclude that some interventions that can be self-initiated by healthy midlife and older adults may ameliorate cognitive aging.