A preliminary study of the safety, feasibility and cognitive efficacy of soy isoflavone supplements in older men and women

Dietary phytoestrogen intakes and cognitive function during the menopausal transition: results from the Study of Women's Health Across the Nation Phytoestrogen Study

OBJECTIVE

Phytoestrogens, which consist mainly of isoflavones, lignans, and coumestans have estrogenic and anti-inflammatory properties. Previous research suggests that higher dietary or supplemental intakes of isoflavones and lignans are related to better cognitive performance in middle-aged and older women.

METHODS

We conducted longitudinal analysis of dietary phytoestrogens and cognitive performance in a cohort of African American, white, Chinese, and Japanese women undergoing the menopausal transition. The tests were Symbol Digit Modalities, East Boston Memory, and Digits Span Backward. Phytoestrogens were assessed using the Food Frequency Questionnaire. We modeled each cognitive score as a function of concurrent value of the primary predictors (highest tertile of isoflavones, lignans, or coumestrol) and covariates including the menopausal transition stage.

RESULTS

Coumestrol and isoflavone intakes were 10 and 25 times greater, respectively, in Asian than in non-Asian participants. During late perimenopause and postmenopause, Asian women with high isoflavone intakes did better on processing speed, but during early perimenopause and postmenopause, high-isoflavone Asian consumers performed worse on verbal memory. The highest isoflavone consumers among non-Asians likewise posted lower verbal memory scores during early perimenopause. A verbal memory benefit of higher dietary lignan consumption was apparent only during late perimenopause, when women from all ethnic/racial groups who were in the highest tertile of intake demonstrated a small advantage. Coumestrol was unrelated to cognitive performance.

CONCLUSIONS

The cognitive effects of dietary phytoestrogens are small, seem to be class-specific, vary by menopause stage and cognitive domain, and differ among ethnic/racial groups (but whether this is related to dose or to host factors cannot be discerned).

A process for high-efficiency isoflavone deglycosylation using Bacillus subtilis natto NTU-18

In order to produce isoflavone aglycosides effectively, a process of isoflavone hydrolysis by Bacillus subtilis natto NTU-18 (BCRC 80390) was established. This process integrates the three stages for the production of isoflavone aglycosides in one single fermenter, including the growth of B. subtilis natto, production of β-glucosidase, deglycosylation of fed isoflavone glycosides. After 8 h of batch culture of B. subtilis natto NTU-18 in 2 L of soy medium, a total of 3 L of soy isoflavone glucoside solution containing 3.0 mg/mL of daidzin and 1.0 mg/mL of genistin was fed continuously over 34 h. The percentage deglycosylation of daidzin and genistin was 97.7% and 94.6%, respectively. The concentration of daidzein and genistein in the broth reached 1,066.8 μg/mL (4.2 mM) and 351 μg/mL (1.3 mM), respectively, and no residual daidzin or genistin was detected. The productivity of the bioconversion of daidzein and genistein over the 42 h of culture was 25.6 mg/L/h and 8.5 mg/L/h, respectively. This showed that this is an efficient bioconversion process for selective estrogen receptor modulator production.

Improving recruitment of older people to research through good practice

There is widespread evidence both of the exclusion of older people from clinical research, and of under-recruitment to clinical trials. This review and opinion piece provides practical advice to assist researchers both to adopt realistic, achievable recruitment rates and to increase the number of older people taking part in research. It analyses 14 consecutive recently published trials, providing the number needed to be screened to recruit one older participant (around 3:1), numbers excluded (up to 49%), drop out rates (5-37%) and whether the planned power was achieved. The value of planning and logistics are outlined, and approaches to optimising recruitment in hospital, primary care and care home settings are discussed, together with the challenges of involving older adults with mental incapacity and those from minority groups in research. The increasingly important task of engaging older members of the public and older patients in research is also discussed. Increasing the participation of older people in research will improve the generalisability of research findings and inform best practice in the clinical management of the growing older population.

Clinical outcomes of a 2-y soy isoflavone supplementation in menopausal women

BACKGROUND

Soy isoflavones are naturally occurring phytochemicals with weak estrogenic cellular effects. Despite numerous clinical trials of short-term isoflavone supplementation, there is a paucity of data regarding longer-term outcomes and safety.

OBJECTIVE

Our aim was to evaluate the clinical outcomes of soy hypocotyl isoflavone supplementation in healthy menopausal women as a secondary outcome of a trial on bone health.

DESIGN

A multicenter, randomized, double-blind, placebo-controlled 24-mo trial was conducted to assess the effects of daily supplementation with 80 or 120 mg aglycone equivalent soy hypocotyl isoflavones plus calcium and vitamin D on the health of 403 postmenopausal women. At baseline and after 1 and 2 y, clinical blood chemistry values were measured and a well-woman examination was conducted, which included a mammogram and a Papanicolaou test. A cohort also underwent transvaginal ultrasound measurements to assess endometrial thickness and fibroids.

RESULTS

The baseline characteristics of the groups were similar. After 2 y of daily isoflavone exposure, all clinical chemistry values remained within the normal range. The only variable that changed significantly was blood urea nitrogen, which increased significantly after 2 y (P = 0.048) but not after 1 y (P = 0.343) in the supplementation groups. Isoflavone supplementation did not affect blood lymphocyte or serum free thyroxine concentrations. No significant differences in endometrial thickness or fibroids were observed between the groups. Two serious adverse events were detected (one case of breast cancer and one case of estrogen receptor-negative endometrial cancer), which was less than the expected population rate for these cancers.

CONCLUSION

Daily supplementation for 2 y with 80-120 mg soy hypocotyl isoflavones has minimal risk in healthy menopausal women. This trial was registered at clinicaltrials.gov as NCT00665860.

Acute effects of 17 β-estradiol and genistein on insulin sensitivity and spatial memory in aged ovariectomized female rats

Aging is characterized by decline in metabolic function and insulin resistance, and both seem to be in the basis of neurodegenerative diseases and cognitive dysfunction. Estrogens prevent age-related changes, and phytoestrogens influence learning and memory. Our hypothesis was that estradiol and genistein, using rapid-action mechanisms, are able to modify insulin sensitivity, process of learning, and spatial memory. Young and aged ovariectomized rats received acute treatment with estradiol or genistein. Aged animals were more insulin-resistant than young. In each age, estradiol and genistein-treated animals were less insulin-resistant than the others, except in the case of young animals treated with high doses of genistein. In aged rats, no differences between groups were found in spatial memory test, showing a poor performance in the water maze task. However, young females treated with estradiol or high doses of genistein performed well in spatial memory task like the control group. Only rats treated with high doses of genistein showed an optimal spatial memory similar to the control group. Conversely, acute treatment with high doses of phytoestrogens improved spatial memory consolidation only in young rats, supporting the critical period hypothesis for the beneficial effects of estrogens on memory. Therefore, genistein treatment seems to be suitable treatment in aged rats in order to prevent insulin resistance but not memory decline associated with aging. Acute genistein treatment is not effective to restore insulin resistance associated to the early loss of ovarian function, although it can be useful to improve memory deficits in this condition.

Borobudur revisited: soy consumption may be associated with better recall in younger, but not in older, rural Indonesian elderly

Previous reports have suggested that high frequent tofu consumption is associated with worse cognitive function in East Asian elderly. Some studies also found an increased risk of dementia with high tofu consumption in those older than 65years of age. Tofu and other soy products, such as tempeh, contain high levels of plant estrogens or isoflavones. This study revisited a rural Central Javanese population (56-97 years of age) who were covered by the Borobudur District Health Centers. Data on cognitive performance were available for n=142 participants. Results showed positive linear associations of weekly tofu (beta=.22, p<0.05) and tempeh (beta=.23, p<0.01) consumption with immediate recall, which were significant in those with an average age of 67 years. In those with an average age of 80 years, the earlier reported negative association of tofu with immediate recall was no longer significant. Lifestyle changes (reduction of tofu consumption after dissemination of results) or "healthy survivor effects" may have been responsible for this finding. These findings may be reminiscent of the "Window of Opportunity" theory, which suggests that estrogenic compounds can exert positive effects on verbal memory, but not in older men and women, when no or negative effects of these compounds on brain cells and cognition have been found. Long-term, placebo-controlled treatment studies should investigate whether tempeh, a fermented soybean product that also contains folate, can maintain cognitive function in middle-aged and elderly participants.

Effects of soy isoflavone extract supplements on blood pressure in adult humans: systematic review and meta-analysis of randomized placebo-controlled trials

OBJECTIVE

Reported effects of different soy products on blood pressure vary. This systematic review and meta-analysis was performed to clarify the effects of soy isoflavone extract supplements on systolic and diastolic blood pressure (SBP and DBP) in adult humans.

METHODS

PubMed, CENTRAL, ICHUSHI, and CNKI were searched in June 2009 for relevant randomized placebo-controlled trials. Study data and indicators of methodological validity were independently extracted by two authors using predefined data fields. Meta-analysis was carried out in Review Manager 5.0.22.

RESULTS

Searches identified 3740 articles, of which 14 randomized controlled trials (789 participants) were included. Daily ingestion of 25-375 mg soy isoflavones (aglycone equivalents) for 2-24 weeks significantly decreased SBP by 1.92 mmHg (95% confidence interval -3.45 to -0.39; P = 0.01) compared with placebo (heterogeneity P = 0.39, fixed effect model) in adults with normal blood pressure and prehypertension. The effect was not lost on sensitivity analysis. Subgroup analyses suggest greater effects in studies longer than 3 months, in Western populations, at lower doses, and in studies at lower risk of bias. Soy isoflavones did not affect DBP [-0.13 (95% confidence interval -1.03 to 0.78) mmHg, P = 0.78; heterogeneity P = 0.20, fixed effect model].

CONCLUSION

Soy isoflavone extracts significantly decreased SBP but not DBP in adult humans, and no dose-response relationship was observed. Further studies are needed to address factors related to the observed effects of soy isoflavones on SBP and to verify the effect in hypertensive patients.

Dietary genistein and equol (4′, 7 isoflavandiol) reduce oxidative stress and protect rats against focal cerebral ischemia

High soy diets reduce injury in rat models of focal cerebral ischemia and are proposed as alternatives to hormone replacement therapy for postmenopausal women. The present study tests the hypothesis that the major soy isoflavone genistein and the daidzein metabolite equol are neuroprotective in transient focal cerebral ischemia in male and ovariectomized (OVX) female rats by inhibiting oxidative stress. Genistein is the primary circulating soy isoflavone in humans, whereas equol is the primary circulating isoflavone in rats. Male and OVX female Sprague-Dawley rats were fed an isoflavone-reduced diet alone or supplemented with genistein (500 ppm) or equol (250 ppm) for 2 wk prior to 90-min transient middle cerebral artery occlusion followed by reperfusion under isoflurane anesthesia. Indices of oxidative stress were determined 24 h after reperfusion, and cerebral injury was evaluated 3 days after reperfusion. Genistein and equol significantly reduced infarct size in both sexes. Further studies in OVX female rats revealed that this neuroprotection was accompanied by a decrease in NAD(P)H oxidase activity and superoxide levels in the brain. In addition, equol reduced plasma thiobarbituric acid reactive substances, and neurological deficits up to 7 days after injury. There were no significant differences in cerebral blood flow among treatment groups. In conclusion, dietary soy isoflavones are neuroprotective in transient focal cerebral ischemia in male and OVX female rats. These isoflavones may protect the brain via increases in endogenous antioxidant mechanisms and reduced oxidative stress.

Cognitive tests used in chronic adult human randomised controlled trial micronutrient and phytochemical intervention studies

In recent years there has been a rapid growth of interest in exploring the relationship between nutritional therapies and the maintenance of cognitive function in adulthood. Emerging evidence reveals an increasingly complex picture with respect to the benefits of various food constituents on learning, memory and psychomotor function in adults. However, to date, there has been little consensus in human studies on the range of cognitive domains to be tested or the particular tests to be employed. To illustrate the potential difficulties that this poses, we conducted a systematic review of existing human adult randomised controlled trial (RCT) studies that have investigated the effects of 24 d to 36 months of supplementation with flavonoids and micronutrients on cognitive performance. There were thirty-nine studies employing a total of 121 different cognitive tasks that met the criteria for inclusion. Results showed that less than half of these studies reported positive effects of treatment, with some important cognitive domains either under-represented or not explored at all. Although there was some evidence of sensitivity to nutritional supplementation in a number of domains (for example, executive function, spatial working memory), interpretation is currently difficult given the prevailing ‘scattergun approach’ for selecting cognitive tests. Specifically, the practice means that it is often difficult to distinguish between a boundary condition for a particular nutrient and a lack of task sensitivity. We argue that for significant future progress to be made, researchers need to pay much closer attention to existing human RCT and animal data, as well as to more basic issues surrounding task sensitivity, statistical power and type I error.

Impact of dietary genistein and aging on executive function in rats

Genistein is an estrogenic soy isoflavone widely promoted for healthy aging, but its effects on cognitive function are not well-understood. We examined the cognitive effects of once daily oral genistein treatment at two doses (approximately 162 microg/kg/day low dose and a 323 microg/kg/day high dose) in ovariectomized young (7 month), middle-aged (16 month), and old (22 month) Long-Evans rats. Operant tasks including delayed spatial alternation (DSA), differential reinforcement of low rates of responding (DRL), and reversal learning that tap prefrontal cortical function were used to assess working memory, inhibitory control/timing, and strategy shifting, respectively. At the conclusion of cognitive testing, brains were collected and relative densities of D1 and D2 dopamine receptors and dopamine transporter (DAT) were measured in the prefrontal cortex. On the DSA task, the high dose old group performed worse than both the high dose young and middle-aged groups. On the DRL task, the high dose of genistein resulted in a marginally significant impairment in the ratio of reinforced to non-reinforced lever presses. This effect was present across age groups. Age effects were also found as old rats performed more poorly than the young and middle-aged rats on the DSA overall. In contrast, middle-aged and old rats made fewer lever presses on the DRL than did the young rats, a pattern of behavior associated with better performance on this task. Moreover, while DAT levels overall decreased with age, genistein treatment produced an increase in DAT expression in old rats relative to similarly aged control rats. D1 and D2 densities did not differ between genistein dose groups or by age. These results highlight the fact that aspects of executive function are differentially sensitive to both genistein exposure and aging and suggest that altered prefrontal dopamine function could potentially play a role in mediating these effects.

Maintaining cognitive health in elderly women

This review indicates that possible preventative activities and lifestyle changes undertaken to maintain cognitive health and prevent dementia in old age may be particularly important in middle age. Risk factors for cardiovascular disease are the same as those for dementia, including its most common form, Alzheimer’s disease. Treating high blood pressure, high cholesterol and thyroid hormone deficiency, maintaining a normal weight, having a healthy diet and engaging in resistance or aerobic exercise can all potentially help to sustain cognitive health. Long-term treatment with estrogenic compounds (> 1 year) does not seem to be indicated and may actually confer risks for dementia in older women over the age of 65 years. The same may be the case for phytoestrogens. The possibility that folate can offset some of the negative effects of phytoestrogens merits more research in this area. Whether there is an optimum age to engage with these types of lifestyle behaviors is currently unclear and also requires additional research.