Vitamin B-Can it prevent cognitive decline? A systematic review and meta-analysis

Plasma homocysteine and longitudinal change in cognitive function among urban adults

BACKGROUND

Cross-sectional and longitudinal studies have inconsistently linked cognitive performance and change over time to an elevated level of homocysteine (Hcy), with few conducted among urban adults.

METHODS

Longitudinal data [Visit 1 (2004-2009) and Visit 2 (2009-2013)] were analyzed from up to 1430 selected Healthy Aging in Neighborhoods of Diversity across the Life Span (HANDLS) participants. Baseline and follow-up blood Hcy was measured, while 11 cognitive function test scores were assessed at either of these two visits. Overall, sex- and race-stratified associations were evaluated using mixed-effects linear regression models, adjusting for key potential confounders. Interaction effects between Hcy and serum levels of folate and vitamin B-12 were also tested.

RESULTS

We found that greater LnHcyv1 was significantly associated with poorer baseline attention based on higher Loge (TRAILS A, in seconds) [β (SE): 0.101 (0.031), P = 0.001]. Heterogeneity was also found by sex and by race. Most notably, among men only, LnHcyv1 was associated with faster decline on the BVRT (# of errors), a measure of visuo-spatial memory (β (SE): 0.297(0.115), P = 0.010, reduced model); while among African American adults only, an elevated and increasing LnHcy over time was associated with faster rate of decline on Loge (TRAILS B, in seconds) [β (SE): +0.012 (0.005), p = 0.008], a measure of executive function. Interactions between Hcy, folate and vitamin B-12 blood exposures were also detected.

CONCLUSIONS

In summary, sex- and race-specific adverse association between elevated Hcy and cognitive performance over time were detected among middle-aged urban adults, in domains of attention, visuo-spatial memory and executive functioning.

7,8-Dihydroxyflavone is a direct inhibitor of human and murine pyridoxal phosphatase

Vitamin B6 deficiency has been linked to cognitive impairment in human brain disorders for decades. Still, the molecular mechanisms linking vitamin B6 to these pathologies remain poorly understood, and whether vitamin B6 supplementation improves cognition is unclear as well. Pyridoxal 5'-phosphate phosphatase (PDXP), an enzyme that controls levels of pyridoxal 5'-phosphate (PLP), the co-enzymatically active form of vitamin B6, may represent an alternative therapeutic entry point into vitamin B6-associated pathologies. However, pharmacological PDXP inhibitors to test this concept are lacking. We now identify a PDXP and age-dependent decline of PLP levels in the murine hippocampus that provides a rationale for the development of PDXP inhibitors. Using a combination of small-molecule screening, protein crystallography, and biolayer interferometry, we discover, visualize, and analyze 7,8-dihydroxyflavone (7,8-DHF) as a direct and potent PDXP inhibitor. 7,8-DHF binds and reversibly inhibits PDXP with low micromolar affinity and sub-micromolar potency. In mouse hippocampal neurons, 7,8-DHF increases PLP in a PDXP-dependent manner. These findings validate PDXP as a druggable target. Of note, 7,8-DHF is a well-studied molecule in brain disorder models, although its mechanism of action is actively debated. Our discovery of 7,8-DHF as a PDXP inhibitor offers novel mechanistic insights into the controversy surrounding 7,8-DHF-mediated effects in the brain.

Prevention, Assessment, and Management of Malnutrition in Older Adults with Early Stages of Cognitive Disorders

Malnutrition is common in older adults, and its risk is greater in those living with dementia. Relative to cognitively healthy peers, the prevalence of malnutrition is also increased in individuals with early stages of cognitive disorders owing to pathophysiological, cognitive, and psychosocial changes related to cognitive impairment. Malnutrition is associated with adverse health outcomes, including faster cognitive and functional decline. Here, we provide an overview of the prevention, assessment, and management of malnutrition in older adults, with a special focus on the aspects that are important to consider in individuals with early stages of cognitive disorders. Strategies to prevent malnutrition include systematic screening for malnourishment using validated tools to detect those at risk. If the screening reveals an increased risk of malnutrition, a detailed assessment including the individual's nutritional, medical, and functional status as well as dietary intake should be performed. The management of malnutrition in the early stages of cognitive disorders should be based on the findings of a comprehensive assessment and be personalized according to the individual's specific characteristics. In the article, we also provide an overview of the evidence on vitamin supplements and specific dietary patterns to prevent cognitive decline or attenuate its progression.

Effects of folic acid supplementation on cognitive impairment: A meta-analysis of randomized controlled trials

OBJECTIVE

With the increasing number of patients with cognitive impairment, nonpharmacological ways to delay cognitive impairment have attracted people's attention, such as lifestyle changes and nutritional supplementation. Folic acid supplementation appears to be a promising treatment option. However, it remains controversial whether folic acid supplementation is effective in delaying adult's cognitive impairment. Therefore, we conducted a meta-analysis to analyze the effects of folic acid supplementation on different cognitive impairments.

METHODS

We systematically searched PubMed, Web of Science, EMbase, Cochrane Central Register of Controlled Trials, China National Knowledge Infrastructure (CNKI), WanFang and VIP databases for randomized controlled trials on January 22, 2024. The included population comprised those diagnosed with cognitive impairment. We included trials that compared folic acid treatment with placebo, other dosing regimens, or other intervention controls. Conducting quality evaluation of included studies according to the Cochrane Risk of Bias tool. Statistical analyses were performed using Review Manager software.

RESULTS

Twenty-two trials, including 3604 participants, met inclusion criteria. Compared with controls, the cognitive function of Alzheimer's disease (AD) patients showed improvement with folic acid supplementation: supplementation with < 3 mg (standardized mean differences (SMD) = 0.15, 95% confidence interval (CI) -0.10 to 0.41), and supplementing with ≥ 3 mg folic acid could improve cognitive function in AD patients (SMD = 1.03, 95% CI 0.18 to 1.88). Additionally, it reduced homocysteine (HCY) levels (mean differences (MD) = -4.74, 95% CI -8.08 to -1.39). In mild cognitive impairment (MCI) patients, cognitive function improved with folic acid supplementation: supplementation with > 400 μg (SMD = 0.38, 95% CI 0.13 to 0.63), and supplementation with ≤ 400 μg (SMD = 1.10, 95% CI 0.88 to 1.31). It also reduced HCY levels at intervention ≤ 6 months (MD = -3.93, 95% CI -5.05 to -2.82) and intervention > 6 months (MD = -4.38, 95% CI -5.15 to -3.61). However, supplementing with folic acid did not improve cognitive function in vascular cognitive impairment (VCI) patients, with folic acid supplements < 3 mg (SMD = -0.07, 95% CI -0.23 to -0.08), folic acid supplements ≥ 3 mg (SMD = 0.46, 95% CI -0.57 to 1.49), however, it reduced HCY levels at intervention > 6 months (MD = -5.91, 95% CI -7.13 to -4.69) and intervention ≤ 6 months (MD = -11.15, 95% CI -12.35 to -9.95).

CONCLUSIONS

Supplement folic acid is beneficial to the cognitive profile of patients with MCI, supplementation with ≥ 3 mg folic acid can improve cognitive function in AD patients.

The role of nutrition in the prevention of cognitive decline

PURPOSE OF REVIEW

Dementia is a growing concern and underscores the urgent need for effective preventive measures targeting modifiable risk factors. Nutrition is a key player in the onset and progression of inflammation and cognitive decline. This review provides a comprehensive overview of the effects of different dietary patterns, vitamins and nutrients for preventing cognitive decline, mainly among healthy individuals and those with mild cognitive impairment.

RECENT FINDINGS

The Mediterranean diet, omega-3 long-chain polyunsaturated fatty acids and B vitamins are the most investigated, with evidence supporting protection against cognitive decline among older adults varying across studies. More recent interventions examined in this review, such as MIND Diet, are promising with positive results, but further research is needed to conclusively establish their efficacy. It is also crucial to consider complete lifestyle as physical activity for preventing cognitive decline.

SUMMARY

Definitive conclusions are difficult to draw. Future studies should adopt a comprehensive approach and focus on multinutrient strategies and whole diets.

Multivitamin Supplementation Improves Memory in Older Adults: A Randomized Clinical Trial

BACKGROUND

Maintenance of cognitive abilities is of critical importance to older adults, yet few effective strategies to slow cognitive decline currently exist. Multivitamin supplementation is used to promote general health; it is unclear whether it favorably affects cognition in older age.

OBJECTIVES

To examine the effect of daily multivitamin/multimineral supplementation on memory in older adults.

METHODS

The COcoa Supplement and Multivitamin Outcomes Study Web (COSMOS-Web) ancillary study (NCT04582617) included 3562 older adults. Participants were randomly assigned to a daily multivitamin supplement (Centrum Silver) or placebo and evaluated annually with an Internet-based battery of neuropsychological tests for 3 y. The prespecified primary outcome measure was change in episodic memory, operationally defined as immediate recall performance on the ModRey test, after 1 y of intervention. Secondary outcome measures included changes in episodic memory over 3 y of follow-up and changes in performance on neuropsychological tasks of novel object recognition and executive function over 3 y.

RESULTS

Compared with placebo, participants randomly assigned to multivitamin supplementation had significantly better ModRey immediate recall at 1 y, the primary endpoint (t(5889) = 2.25, P = 0.025), as well as across the 3 y of follow-up on average (t(5889) = 2.54, P = 0.011). Multivitamin supplementation had no significant effects on secondary outcomes. Based on cross-sectional analysis of the association between age and performance on the ModRey, we estimated that the effect of the multivitamin intervention improved memory performance above placebo by the equivalent of 3.1 y of age-related memory change.

CONCLUSIONS

Daily multivitamin supplementation, compared with placebo, improves memory in older adults. Multivitamin supplementation holds promise as a safe and accessible approach to maintaining cognitive health in older age. This trial was registered at clinicaltrials.gov as NCT04582617.

The Effects of Methylfolate on Cognitive Decline and Dementia: A Protocol for Systematic Review and Meta-Analysis

INTRODUCTION

Dementia and cognitive decline are highly prevalent in later life and are growing public health concerns worldwide due to the increasing aging population. Individuals diagnosed with dementia have reduced mental function, resulting in social and cognitive skill deficits, increased dependence, and reduced autonomy-all of which are conditions associated with higher mortality rates. This systematic review aims to assess the effectiveness of treating dementia and cognitive decline with methylfolate. The main outcomes analyzed will be dementia and changes in cognitive function measured by different instruments in older adults treated with methylfolate. Secondary outcomes, such as inflammatory markers, plasma folic-acid levels, and total homocysteine, will also be assessed.

METHODS AND ANALYSIS

This study will be carried out in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. This protocol is registered in the International Prospective Registry of Systematic Reviews, under the code CRD42021275755. We will include clinical trials conducted with older adults diagnosed with dementia or cognitive decline and treated with folic acid. The searches will be conducted on the PubMed, Scopus, and Embase databases, and the articles will be selected by reading their titles and abstracts first, followed by the full text. The quality of the selected studies will be assessed using GRADE and the risk of bias will be assessed using the Downs-and-Black method.

ETHICS AND DISSEMINATION

The results will be presented at scientific conferences and disseminated by publishing a scientific article in an international English-language journal. We hope to find robust and significant evidence regarding the effectiveness of methylfolate supplementation in improving dementia symptoms and cognitive decline among older adults. By systematizing this evidence and possibly performing a meta-analysis study, we expect to significantly contribute to the treatment of this health problem, reduce mortality, and improve the quality of life and health of this population, boosting the development of medical protocols capable of reducing the financial effects of public health.

Levodopa, homocysteine and Parkinson's disease: What's the problem?

Elevated circulating homocysteine levels have been associated with cognitive impairment and cardio-cerebro-vascular events. Levodopa treatment of Parkinson's disease tends to further elevate circulating homocysteine levels due to the metabolism of levodopa via catechol-O-methyltransferase (COMT). COMT co-factors are vitamins B12, B6 and folic acid. Accumulating deficiencies of these vitamins are presumed to be the substrate for the homocysteine elevation. B-vitamin therapy reduces homocysteine levels. This begs the question of whether Parkinson's disease patients on levodopa should be concurrently treated with ongoing B-vitamin therapy (versus long-term monitoring of B-vitamins/homocysteine). There is a substantial literature on this topic that has accumulated over the last quarter-century, and this topic is still debated. This review summarizes the relevant literature with the aim of approximating closure on this issue. Also, noteworthy is that Parkinson's disease patients with renal insufficiency may not tolerate cyanocobalamin, the standard oral B12 supplement due to facilitation of renal decline; alternatives are discussed.

The role of mixed B vitamin intakes on cognitive performance: Modeling, genes and miRNAs involved

OBJECTIVE

To assess the relationships between mixed B vitamin intakes (B1, B2, B3, B6, B9, B12) and cognitive performance, as well as their molecular mechanisms.

METHODS

The associations of mixed B vitamin intakes with cognitive function were assessed using multivariate regression models, weighted quantile sum (WQS), quantile g-computation (qgcomp), and Bayesian kernel machine regression (BKMR). GeneMANIA, Comparative Toxicogenomics Database, MIENTURNET, miRNAsong were employed as the main data-mining methods.

RESULTS

Overall effects of the B vitamin intake mixture were significantly associated with global cognition in the WQS, qgcomp, and BKMR models. A mixture of B vitamins (B1, B2, B3, B9) interacted with the five genes (IL1B, BCL2, CASP3, BAX, PTGS2) and was associated with better cognitive function, especially CASP3 and BAX. Physical interactions (77.6%) were observed to be the most important interactions in gene networks. The IL-18 signaling pathway, apoptosis, and Alzheimer's disease were annotated as the key molecular mechanisms involved in mixed B vitamins' improving cognitive function. NFKB1, ATF3, and NR3C1 were the key significant transcription factors associated with cognitive function targeted by a mixture of B vitamins. The strong interaction and expression of hsa-miR-34a-5p, hsa-miR-128-3p, hsa-miR-181a-5p, and hsa-miR-204-5p are involved in mixed B vitamins' better cognitive performance. We also created and evaluated miRNA sponge sequences for these miRNAs, which might be used to alleviate cognitive decline. The cutoff thresholds for B vitamin intake levels that are associated with cognition performance were reported.

CONCLUSIONS

Given the increased incidence of dementia across the world, increasing daily mixed B vitamin intake via regular meals may contribute to minimizing dementia risk. Further studies are warranted to identify these links in well-characterized cohorts of diverse populations, either independently or together.

The Roles of Long-Term Hyperhomocysteinemia and Micronutrient Supplementation in the AppNL–G–F Model of Alzheimer’s Disease

A causal contribution of hyperhomocysteinemia to cognitive decline and Alzheimer’s disease (AD), as well as potential prevention or mitigation of the pathology by dietary intervention, have frequently been subjects of controversy. In the present in vivo study, we attempted to further elucidate the impact of elevated homocysteine (HCys) and homocysteic acid (HCA) levels, induced by dietary B-vitamin deficiency, and micronutrient supplementation on AD-like pathology, which was simulated using the amyloid-based App^NL–G–F knock-in mouse model. For this purpose, cognitive assessment was complemented by analyses of ex vivo parameters in whole blood, serum, CSF, and brain tissues from the mice. Furthermore, neurotoxicity of HCys and HCA was assessed in a separate in vitro assay. In confirmation of our previous study, older App^NL–G–F mice also exhibited subtle phenotypic impairment and extensive cerebral amyloidosis, whereas dietary manipulations did not result in significant effects. As revealed by proximity extension assay-based proteome analysis, the App^NL–G–F genotype led to an upregulation of AD-characteristic neuronal markers. Hyperhomocysteinemia, in contrast, indicated mainly vascular effects. Overall, since there was an absence of a distinct phenotype despite both a significant amyloid-β burden and serum HCys elevation, the results in this study did not corroborate the pathological role of amyloid-β according to the “amyloid hypothesis,” nor of hyperhomocysteinemia on cognitive performance. Nevertheless, this study aided in further characterizing the App^NL–G–F model and in elucidating the role of HCys in diverse biological processes. The idea of AD prevention with the investigated micronutrients, however, was not supported, at least in this mouse model of the disease.

US Older Adults That Consume Avocado or Guacamole Have Better Cognition Than Non-consumers: National Health and Nutrition Examination Survey 2011-2014

Purpose: The goal of this study is to examine how avocado relates to cognitive function among older adults. Methods: A total of 2,886 National Health and Nutrition Examination Survey 2011-2014 participants aged 60 or older met the eligibility criteria and were included of our cross-sectional study. Participants were binarily classified as avocado consumers (i.e., reported consuming any avocado/guacamole in either 24-h dietary recalls) or non-consumers. Cognitive performance was evaluated with: Consortium to Establish a Registry for Alzheimer's disease (CERAD)-immediate and delayed recall (IWR/DWR), the Animal Fluency test, and the Digit Symbol Substitution Test. We calculated the education-dependent z-scores for each subject because education level can impact cognitive function. Global cognitive score, an average of the z-scores for each cognitive test, was calculated in participants who had completed all four tests. To account for relevant covariates, we tested for mean differences in cognition between consumers and non-consumers using independent sample t-tests and ANCOVA, special cases of ordinary least squares regression. Results: Avocado consumers had significantly better cognitive scores across all cognitive tests and the global cognition score (p < 0.05) in the unadjusted model. Some mean differences attenuated after adjusting for potential confounders, but others remained significant. Compared to non-consumers, avocado consumers had significantly higher z-scores of 0.15, 0.15, and 0.11 for CERAD IWR and DWR, and global cognition score, respectively (all p < 0.05 in adjusted models). Conclusion: Avocado consumption was associated with significantly better IWR, DWR, and the overall global cognition score, which remained significant when controlling for all relevant confounders.

Hyperhomocysteinemia: Metabolic Role and Animal Studies with a Focus on Cognitive Performance and Decline-A Review

Disturbances in the one-carbon metabolism are often indicated by altered levels of the endogenous amino acid homocysteine (HCys), which is additionally discussed to causally contribute to diverse pathologies. In the first part of the present review, we profoundly and critically discuss the metabolic role and pathomechanisms of HCys, as well as its potential impact on different human disorders. The use of adequate animal models can aid in unravelling the complex pathological processes underlying the role of hyperhomocysteinemia (HHCys). Therefore, in the second part, we systematically searched PubMed/Medline for animal studies regarding HHCys and focused on the potential impact on cognitive performance and decline. The majority of reviewed studies reported a significant effect of HHCys on the investigated behavioral outcomes. Despite of persistent controversial discussions about equivocal findings, especially in clinical studies, the present evaluation of preclinical evidence indicates a causal link between HHCys and cognition-related- especially dementia-like disorders, and points out the further urge for large-scale, well-designed clinical studies in order to elucidate the normalization of HCys levels as a potential preventative or therapeutic approach in human pathologies.

The neuropsychiatric effects of nitrous oxide and low vitamin B12

This narrative review article aims to update knowledge on the neuropsychiatric complications of nitrous oxide use and low vitamin B12. We consider common forms and uses of nitrous oxide (N2O) and review its mechanism of action, and then explore the potential impacts of use. In particular, neuropsychiatric effects mediated by low vitamin B12 are considered and the correct interpretation of laboratory results explored. This is of particular importance as where vitamin B12 is inactivated by chronic nitrous oxide use, blood test levels of vitamin B12 may not reflect the quantity of functional B12 in patients.

The preventive efficacy of vitamin B supplements on the cognitive decline of elderly adults: a systematic review and meta-analysis

Background

The irreversibility of cognitive impairment of Alzheimer’s disease (AD) prompts that preventing or delaying the onset of AD should be a public health priority. Vitamin B supplements can lower the serum homocysteine (Hcy) level, but whether it can prevent cognitive decline or not remains unclear. We aimed to evaluate the preventive efficacy of vitamin B supplements on the cognitive decline of elderly adults.

Methods

We searched PubMed, Embase, The Cochrane Central Register of Controlled Trials (CENTRAL), Web of Science, Scopus, Science Direct, PsycINFO from inception to December 1, 2019, and then updated the retrieved results on June 1, 2020. The randomized controlled trials (RCTs) which evaluated the efficacy of vitamin B in mild cognitive impairment (MCI) patients or elderly adults without cognitive impairment were selected. Standardized mean difference (SMD) or mean difference (MD) as well as their 95 % confidence interval (CI) were calculated by performing random effects models or fixed effects models.

Results

A total of 21 RCTs involving 7571 participants were included for meta-analysis. The forest plots showed that there is significant effect in global cognitive function (15 RCTs, SMD: 0.36; 95 % CI: 0.18 to 0.54, P < 0.01) and Hcy (11 RCTs, MD: -4.59; 95 %CI: -5.51 to -3.67, P < 0.01), but there is no effect in information processing speed (10 RCTs, SMD: 0.06; 95 % CI: -0.12 to 0.25, P = 0.49), episodic memory (15 RCTs, SMD: 0.10; 95 % CI: -0.04 to 0.25, P = 0.16), executive function (11 RCTs, SMD: -0.21; 95 % CI: -0.49 to 0.06, P = 0.13). The value of effect size and heterogeneity did not vary apparently when excluding the low-quality studies, so we could believe that the results of meta-analysis were robust.

Conclusions

Vitamin B supplements might delay or maintain the cognitive decline of elderly adults. We can recommend that the vitamin B supplements should be considered as a preventive medication to MCI patients or elderly adults without cognitive impairment. More well-designed RCTs with large sample sizes were required to clarify the preventive efficacy in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12877-021-02253-3.

Effects of Vitamin B12 Supplementation on Cognitive Function, Depressive Symptoms, and Fatigue: A Systematic Review, Meta-Analysis, and Meta-Regression

Vitamin B12 is often used to improve cognitive function, depressive symptoms, and fatigue. In most cases, such complaints are not associated with overt vitamin B12 deficiency or advanced neurological disorders and the effectiveness of vitamin B12 supplementation in such cases is uncertain. The aim of this systematic review and meta-analysis of randomized controlled trials (RCTs) is to assess the effects of vitamin B12 alone (B12 alone), in addition to vitamin B12 and folic acid with or without vitamin B6 (B complex) on cognitive function, depressive symptoms, and idiopathic fatigue in patients without advanced neurological disorders or overt vitamin B12 deficiency. Medline, Embase, PsycInfo, Cochrane Library, and Scopus were searched. A total of 16 RCTs with 6276 participants were included. Regarding cognitive function outcomes, we found no evidence for an effect of B12 alone or B complex supplementation on any subdomain of cognitive function outcomes. Further, meta-regression showed no significant associations of treatment effects with any of the potential predictors. We also found no overall effect of vitamin supplementation on measures of depression. Further, only one study reported effects on idiopathic fatigue, and therefore, no analysis was possible. Vitamin B12 supplementation is likely ineffective for improving cognitive function and depressive symptoms in patients without advanced neurological disorders.

Effects of Alzheimer-Like Pathology on Homocysteine and Homocysteic Acid Levels-An Exploratory In Vivo Kinetic Study

Hyperhomocysteinemia has been suggested potentially to contribute to a variety of pathologies, such as Alzheimer’s disease (AD). While the impact of hyperhomocysteinemia on AD has been investigated extensively, there are scarce data on the effect of AD on hyperhomocysteinemia. The aim of this in vivo study was to investigate the kinetics of homocysteine (HCys) and homocysteic acid (HCA) and effects of AD-like pathology on the endogenous levels. The mice received a B-vitamin deficient diet for eight weeks, followed by the return to a balanced control diet for another eight weeks. Serum, urine, and brain tissues of App^NL-G-F knock-in and C57BL/6J wild type mice were analyzed for HCys and HCA using LC-MS/MS methods. Hyperhomocysteinemic levels were found in wild type and knock-in mice due to the consumption of the deficient diet for eight weeks, followed by a rapid normalization of the levels after the return to control chow. Hyperhomocysteinemic App^NL-G-F mice had significantly higher HCys in all matrices, but not HCA, compared to wild type control. Higher serum concentrations were associated with elevated levels in both the brain and in urine. Our findings confirm a significant impact of AD-like pathology on hyperhomocysteinemia in the App^NL-G-F mouse model. The immediate normalization of HCys and HCA after the supply of B-vitamins strengthens the idea of a B-vitamin intervention as a potentially preventive treatment option for HCys-related disorders such as AD.