Vitamin B₁₂ status, cognitive decline and dementia: a systematic review of prospective cohort studies

Poor vitamin B₁₂ status may lead to the development of cognitive decline and dementia but there is a large variation in the quality, design of and results reported from these investigations. We have undertaken a systematic review of the evidence for the association between vitamin B₁₂ status and cognitive decline in older adults. A database search of the literature to 2011 was undertaken, using keywords related to vitamin B₁₂ and cognition. All prospective cohort studies assessing the association of serum vitamin B₁₂ or biomarkers were included. Quality assessment and extraction of the data were undertaken by two researchers. The quality assessment tool assigns a positive, neutral or negative rating. Of 3772 published articles, thirty-five cohort studies (n 14 325 subjects) were identified and evaluated. No association between serum vitamin B₁₂ concentrations and cognitive decline or dementia was found. However, four studies that used newer biomarkers of vitamin B₁₂ status (methylmalonic acid and holotranscobalamin (holoTC)) showed associations between poor vitamin B₁₂ status and the increased risk of cognitive decline or dementia diagnosis. In general, the studies were of reasonable quality (twenty-one positive, ten neutral and four negative quality) but of short duration and inadequate subject numbers to determine whether an effect exists. Future studies should be of adequate duration (at least 6 years), recruit subjects from the seventh decade, choose markers of vitamin B₁₂ status with adequate specificity such as holoTC and/or methylmalonic acid and employ standardised neurocognitive assessment tools and not screening tests in order to ascertain any relationship between vitamin B₁₂ status and cognitive decline.

Status of vitamins B-12 and B-6 but not of folate, homocysteine, and the methylenetetrahydrofolate reductase C677T polymorphism are associated with impaired cognition and depression in adults

The C677T polymorphism of the methylenetetrahydrofolate reductase (MTHFR) gene differs in frequency in various ethnic groups that have differing prevalence of age-related cognitive impairments. We used a series of neuro-psychological tests to examine the association of the MTHFR C677T polymorphism with cognition and depression and also to assess whether genotype modifies the association of folate and homocysteine with these outcomes. This study analyzed pooled cross-sectional data from 2 ethnically diverse cohorts of community-living adults: the Boston Puerto Rican Health Study (n = 939) and the Nutrition, Aging, and Memory in Elders study (n = 1017). Individuals in both cohorts underwent anthropometric and laboratory measurements and dietary and health assessments using validated questionnaires between the years 2003 and 2007. Cognitive outcomes included measures of global cognition [Mini-Mental Status Exam (MMSE)], depression (Center for Epidemiological Studies Depression Scale), and 3 factor scores for the domains of attention, executive function, and memory that were derived from a detailed set of neuropsychological tests. Low plasma vitamin B-12 concentrations were associated with poorer MMSE scores and higher depression scores, and low vitamin B-6 concentrations were associated with lower MMSE and worse attention and executive function in the multivariate analysis. In contrast, MTHFR genotype, folate, and homocysteine were not associated with cognition or depression in either ethnicity-pooled or stratified analysis. The current study did not find evidence of an association between the MTHFR C677T TT genotype and impaired cognition or depression in a population with adequate folate status and a high prevalence of cognitive impairment and depression.

Conversion from mild cognitive impairment to dementia: influence of folic acid and vitamin B12 use in the VITA cohort

OBJECTIVE

Increased serum homocysteine and low folate levels are associated with a higher rate of conversion to dementia. This study examined the influence of vitamin B12/folic acid intake on the conversion from mild cognitive impairment (MCI) to dementia.

PARTICIPANTS

A community dwelling cohort of older adults (N=81) from the Vienna Transdanube aging study with MCI.

DESIGN

Prospective study with a retrospective evaluation of vitamin intake.

MEASUREMENTS

Laboratory measurements, brain magnetic resonance imaging, and cognitive functioning were assessed at baseline and at five-year follow-up.

RESULTS

The self-reported combined use of folic acid and vitamin B12 for more than one year was associated with a lower conversion rate to dementia. Serum levels of homocysteine and vitamin B12 as measured at baseline or at five years were not associated with conversion. Higher folate levels at baseline in females predicted a lower conversion rate to dementia. The assessment of brain morphological parameters by magnetic resonance imaging revealed higher serum folate at baseline, predicting lower medial temporal lobe atrophy and higher levels of homocysteine at baseline, predicting moderate/severe global brain atrophy at five years. Users of vitamin B12 or folate, independent of time and pattern of use, had lower grades of periventricular hyperintensities and lower grades of deep white matter lesions as compared to non-users.

CONCLUSIONS

These results from a middle European study support observations on the protective ability of folate in MCI patients with respect to conversion to dementia; they also point to a participation of homocysteine metabolism on processes associated with brain atrophy.

Cognitive and clinical outcomes of homocysteine-lowering B-vitamin treatment in mild cognitive impairment: a randomized controlled trial

BACKGROUND

Homocysteine is a risk factor for Alzheimer's disease. In the first report on the VITACOG trial, we showed that homocysteine-lowering treatment with B vitamins slows the rate of brain atrophy in mild cognitive impairment (MCI). Here we report the effect of B vitamins on cognitive and clinical decline (secondary outcomes) in the same study.

METHODS

This was a double-blind, single-centre study, which included participants with MCI, aged ≥ 70 y, randomly assigned to receive a daily dose of 0.8 mg folic acid, 0.5 mg vitamin B(12) and 20 mg vitamin B(6) (133 participants) or placebo (133 participants) for 2 y. Changes in cognitive or clinical function were analysed by generalized linear models or mixed-effects models.

RESULTS

The mean plasma total homocysteine was 30% lower in those treated with B vitamins relative to placebo. B vitamins stabilized executive function (CLOX) relative to placebo (P = 0.015). There was significant benefit of B-vitamin treatment among participants with baseline homocysteine above the median (11.3 µmol/L) in global cognition (Mini Mental State Examination, P < 0.001), episodic memory (Hopkins Verbal Learning Test-delayed recall, P = 0.001) and semantic memory (category fluency, P = 0.037). Clinical benefit occurred in the B-vitamin group for those in the upper quartile of homocysteine at baseline in global clinical dementia rating score (P = 0.02) and IQCODE score (P = 0.01).

CONCLUSION

In this small intervention trial, B vitamins appear to slow cognitive and clinical decline in people with MCI, in particular in those with elevated homocysteine. Further trials are needed to see if this treatment will slow or prevent conversion from MCI to dementia.

Plasma free choline, betaine and cognitive performance: the Hordaland Health Study

Choline and betaine are nutrients involved in one-carbon metabolism. Choline is essential for neurodevelopment and brain function. We studied the associations between cognitive function and plasma concentrations of free choline and betaine. In a cross-sectional study, 2195 subjects (55 % women), aged 70-74 years, underwent extensive cognitive testing including the Kendrick Object Learning Test (KOLT), Trail Making Test (part A, TMT-A), modified versions of the Digit Symbol Test (m-DST), Block Design (m-BD), Mini-Mental State Examination (m-MMSE) and Controlled Oral Word Association Test (COWAT). Compared with low concentrations, high choline (>8·4 μmol/l) was associated with better test scores in the TMT-A (56·0 v. 61·5, P=0·004), m-DST (10·5 v. 9·8, P=0·005) and m-MMSE (11·5 v. 11·4, P=0·01). A generalised additive regression model showed a positive dose-response relationship between the m-MMSE and choline (P=0·012 from a corresponding linear regression model). Betaine was associated with the KOLT, TMT-A and COWAT, but after adjustments for potential confounders, the associations lost significance. Risk ratios (RR) for poor test performance roughly tripled when low choline was combined with either low plasma vitamin B₁₂ (≤257 pmol/l) concentrations (RR(KOLT)=2·6, 95 % CI 1·1, 6·1; RR(m-MMSE)=2·7, 95 % CI 1·1, 6·6; RR(COWAT)=3·1, 95 % CI 1·4, 7·2) or high methylmalonic acid (MMA) (≥3·95 μmol/l) concentrations (RR(m-BD)=2·8, 95 % CI 1·3, 6·1). Low betaine (≤31·1 μmol/l) combined with high MMA was associated with elevated RR on KOLT (RR(KOLT)=2·5, 95 % CI 1·0, 6·2). Low plasma free choline concentrations are associated with poor cognitive performance. There were significant interactions between low choline or betaine and low vitamin B₁₂ or high MMA on cognitive performance.

Homocysteine, methylenetetrahydrofolate reductase C677T polymorphism and cognitive impairment: the health in men study

High total plasma homocysteine (tHcy) has been associated with cognitive impairment in later life, but it is unclear if this association is causal or is due to confounding. The C677T polymorphism of the 5,10 methylenetetrahydrofolate reductase gene (MTHFR) increases basal tHcy, but its contribution to cognitive impairment has not been established. We designed this study to determine if tHcy is causally related to cognitive impairment in later life by investigating its association with high tHcy and the MTHFR-C677T polymorphism. We recruited 1778 older men from the Health in Men Study cohort and established caseness on the basis of the participants' scores on a Telephone Interview for Cognitive Status score 27 in 2008. Exposure to tHcy, gene status and other variables of interest were obtained from assessments 4-7 years earlier. Multivariate logistic regression showed that the odds of cognitive impairment increased with a doubling of tHcy (adjusted odds ratio, OR 1.36; 95% confidence interval, 95% CI 1.02-1.82). Compared with the wild CC genotype, participants with the MTHFR-TT genotype had 46% greater odds of cognitive impairment (OR 1.46, 95% CI 1.01-2.11, P=0.043). The results of this study are consistent with, but do not prove the hypothesis that high tHcy causes cognitive impairment in later life.

Butyrylcholinesterase genotype and gender influence Alzheimer's disease phenotype

Retrospective data are presented to support a spectrum of early Alzheimer's disease (AD) along a continuum defined by gender and genotype. The putative neurodegenerative mechanisms driving distinct phenotypes at each end of the spectrum are glial hypoactivity associated with early failure of synaptic cholinergic neurotransmission and glial overactivation associated with loss of neural network connectivity due to accelerated age-related breakdown of myelin. In early AD, male butyrylcholinesterase K-variant carriers with one or two apolipoprotein ɛ4 alleles have prominent medial temporal atrophy, synaptic failure, cognitive decline, and accumulation of aggregated beta-amyloid peptide. Increasing synaptic acetylcholine in damaged but still functional cholinergic synapses improves cognitive symptoms, whereas increasing the ability of glia to support synapses and to clear beta-amyloid peptide might be disease-modifying. Conversely, chronic glial overactivation can also drive degenerative processes and in butyrylcholinesterase K-variant negative females generalized glial overactivation may be the main driver from mild cognitive impairment to AD. Females are more likely than males to have accelerated age-related myelin breakdown, more widespread white matter loss, loss of neural network connectivity, whole brain atrophy, and functional decline. Increasing extracellular acetylcholine levels blocks glial activation, reduces myelin loss and damage to neural network connectivity, and is disease-modifying. Between extremes characterized by gender, genotype, and age, pathophysiology may be mixed and this spectrum may explain much of the heterogeneity of amnestic mild cognitive impairment. Preservation of the functional integrity of the neural network may be an important component of strengthening cognitive reserve and significantly delaying the onset and progression of dementia, particularly in females. Prospective confirmation of these hypotheses is required. Implications for future research and therapeutic opportunities are discussed.

Homocysteine, grey matter and cognitive function in adults with cardiovascular disease

BACKGROUND

Elevated total plasma homocysteine (tHcy) has been associated with cognitive impairment, vascular disease and brain atrophy.

METHODS

We investigated 150 volunteers to determine if the association between high tHcy and cerebral grey matter volume and cognitive function is independent of cardiovascular disease.

RESULTS

Participants with high tHcy (≥15 µmol/L) showed a widespread relative loss of grey matter compared with people with normal tHcy, although differences between the groups were minimal once the analyses were adjusted for age, gender, diabetes, hypertension, smoking and prevalent cardiovascular disease. Individuals with high tHcy had worse cognitive scores across a range of domains and less total grey matter volume, although these differences were not significant in the adjusted models.

CONCLUSIONS

Our results suggest that the association between high tHcy and loss of cerebral grey matter volume and decline in cognitive function is largely explained by increasing age and cardiovascular diseases and indicate that the relationship is not causal.

B-vitamins for neuroprotection: narrowing the evidence gap

A compelling and extensive epidemiological literature documents the strong association of inadequate status of folate, vitamin B₁₂, and to a lesser degree vitamin B6, with increased risk of neurodegenerative and cerebrovascular disease. Mildly elevated plasma total homocysteine, which is biochemically related to low status of these B-vitamins, is similarly associated with increased risk for these conditions. This, together with experimental data showing that experimental B-vitamin deficiency and/or hyperhomocysteinemia can cause a variety of neurological and vascular deficits in animals, has provided the evidence base and motivation for a growing number of large randomized, double-blind clinical trials aimed at determining the efficacy and safety of B-vitamin supplementation for preserving cognitive function in older adults. Despite some encouraging trials showing benefit of B-vitamins for slowing brain atrophy and cognitive decline, the majority of these studies have not demonstrated that B-vitamin supplementation has protective or therapeutic cognitive benefit. There are many possible explanations for the inconsistency between the clinical trials and for the discrepancy between their findings and the predictions of the epidemiological evidence. Among these are the possibility of inadequate hypotheses guiding the trials, design limitations of the individual trials, and inherent limitations of nutritional randomized clinical trials. Resolving these issues will be crucial for designing definitive trials and ultimately for guiding nutritional interventions for cognitive protection.

Associations between serum homocysteine, holotranscobalamin, folate and cognition in the elderly: a longitudinal study

OBJECTIVES

To examine the associations between serum homocysteine (tHcy), holotranscobalamin (holoTC, the biologically active fraction of vitamin B12) and folate and cognitive functioning in a longitudinal population-based study of Finnish elderly subjects.

SUBJECTS AND DESIGN

tHcy, holoTC and folate were measured at baseline in 274 dementia-free subjects aged 65-79years from the Cardiovascular Risk Factors, Aging and Dementia study. Subjects were re-examined 7years later, and global cognition, episodic memory, executive functioning, verbal expression and psychomotor speed were assessed.

RESULTS

Higher baseline tHcy levels were associated with poorer performance in global cognition, relative difference: 0.90 [95% confidence interval (CI) 0.81-0.99]; episodic memory: 0.87 (95% CI 0.77-0.99); executive functions: 0.86 (95% CI 0.75-0.98); and verbal expression: 0.89 (95% CI 0.81-0.97) at follow-up. Increased holoTC levels were related to better performance on global cognition: 1.09 (95% CI 1.00-1.19); executive functions: 1.11 (95% CI 1.01-1.21); and psychomotor speed: 1.13 (95% CI 1.01-1.26). After excluding 20 cases of incident dementia, increased tHcy remained associated with poorer performance in episodic memory, execution functions and verbal expression. Higher holoTC levels tended to be related to better performance in executive functions and psychomotor speed, while elevated serum folate concentrations were significantly related to higher scores in global cognition and verbal expression tests.

CONCLUSIONS

tHcy, holoTC and folate levels are related to cognitive performance 7years later even in nondemented elderly subjects. Randomized trials are needed to determine the impact of vitamin B12 and folate supplementation on preventing cognitive decline in the elderly.

Metabolism and neurotoxicity of homocysteine thiolactone in mice: protective role of bleomycin hydrolase

Genetic or nutritional disorders in homocysteine (Hcy) metabolism elevate Hcy-thiolactone and cause heart and brain diseases. Hcy-thiolactone has been implicated in these diseases because it has the ability to modify protein lysine residues and generate toxic N-Hcy-proteins with auto-immunogenic, pro-thrombotic, and amyloidogenic properties. Bleomycin hydrolase (Blmh) has the ability to hydrolyze L-Hcy-thiolactone (but not D-Hcy-thiolactone) to Hcy in vitro, but whether this reflects a physiological function has been unknown. Here, we show that Blmh (-/-) mice excreted in urine 1.8-fold more Hcy-thiolactone than wild-type Blmh (+/+) animals (P = 0.02). Hcy-thiolactone was elevated 2.3-fold in brains (P = 0.004) and 2.0-fold in kidneys (P = 0.047) of Blmh (-/-) mice relative to Blmh (+/+) animals. Plasma N-Hcy-protein was elevated in Blmh (-/-) mice fed a normal (2.3-fold, P < 0.001) or hyperhomocysteinemic diet (1.5-fold, P < 0.001), compared with Blmh (+/+) animals. More intraperitoneally injected L-Hcy-thiolactone was recovered in plasma in Blmh (-/-) mice than in wild-type Blmh (+/+) animals (83.1 vs. 39.3 μM, P < 0.0001). In Blmh (+/+) mice injected intraperitoneally with D-Hcy-thiolactone, D,L-Hcy-thiolactone, or L-Hcy-thiolactone, 88, 47, or 6.3%, respectively, of the injected dose was recovered in plasma. The incidence of seizures induced by L-Hcy-thiolactone injections (3,700 nmol/g body weight) was higher in Blmh (-/-) than in Blmh (+/+) mice (93.8 vs. 29.5%, P < 0.001). Using the Blmh null mice, we provide the first direct evidence that a specific Hcy metabolite, Hcy-thiolactone, rather than Hcy itself, is neurotoxic in vivo. Taken together, our findings indicate that Blmh protects mice against L-Hcy-thiolactone toxicity by metabolizing it to Hcy and suggest a mechanism by which Blmh might protect against neurodegeneration associated with hyperhomocysteinemia and Alzheimer's disease.

Rationale and design of the B-PROOF study, a randomized controlled trial on the effect of supplemental intake of vitamin B12 and folic acid on fracture incidence

Background

Osteoporosis is a major health problem, and the economic burden is expected to rise due to an increase in life expectancy throughout the world. Current observational evidence suggests that an elevated homocysteine concentration and poor vitamin B₁₂ and folate status are associated with an increased fracture risk. As vitamin B₁₂ and folate intake and status play a large role in homocysteine metabolism, it is hypothesized that supplementation with these B-vitamins will reduce fracture incidence in elderly people with an elevated homocysteine concentration.

Methods/Design

The B-PROOF (B-Vitamins for the PRevention Of Osteoporotic Fractures) study is a randomized double-blind placebo-controlled trial. The intervention comprises a period of two years, and includes 2919 subjects, aged 65 years and older, independently living or institutionalized, with an elevated homocysteine concentration (≥ 12 μmol/L). One group receives daily a tablet with 500 μg vitamin B₁₂ and 400 μg folic acid and the other group receives a placebo tablet. In both tablets 15 μg (600 IU) vitamin D is included. The primary outcome of the study is osteoporotic fractures. Measurements are performed at baseline and after two years and cover bone health i.e. bone mineral density and bone turnover markers, physical performance and physical activity including falls, nutritional intake and status, cognitive function, depression, genetics and quality of life. This large multi-center project is carried out by a consortium from the Erasmus MC (Rotterdam, the Netherlands), VUmc (Amsterdam, the Netherlands) and Wageningen University, (Wageningen, the Netherlands), the latter acting as coordinator.

Discussion

To our best knowledge, the B-PROOF study is the first intervention study in which the effect of vitamin B₁₂ and folic acid supplementation on osteoporotic fractures is studied in a general elderly population. We expect the first longitudinal results of the B-PROOF intervention in the second semester of 2013. The results of this intervention will provide evidence on the efficacy of vitamin B₁₂ and folate supplementation in the prevention of osteoporotic fractures.

Trial Registration

The B-PROOF study is registered with the Netherlands Trial (NTR NTR1333) and with ClinicalTrials.gov (NCT00696514).

Age-related lysosomal dysfunction: an unrecognized roadblock for cobalamin trafficking?

Vitamin-B(12) is a generic term for corrinoid compounds that exhibit the biological activity of cyanocobalamin and are collectively referred to as cobalamins. Methylcobalamin and 5-deoxyadenosylcobalamin are the active cobalamins in human metabolism. Cobalamin plays a crucial role in the maintenance of homocysteine and methylmalonyl-CoA homeostasis and is required for erythrocyte formation and DNA synthesis. Data from human and animal studies indicate that cobalamin deficiency impairs neuronal function; a process that is thought to contribute to age-related cognitive decline and dementia. Cobalamin deficiency also results in dysfunction of the peripheral nervous system; among other disorders. Although there is a detailed understanding of the biochemical pathways that are perturbed in cobalamin deficiency, the mechanisms underlying age-related dyshomeostasis in such pathways remain to be addressed. Because cobalamin utilization is dependent on its efficient transit through lysosomes, and mounting evidence indicates that lysosomal function deteriorates in aging long-lived post-mitotic cells such as neurons, in the present article we review published data that supports the proposition that impaired lysosomal processing of cobalamin may play a significant role in age-related (neuro) degenerative diseases.

Folate, vitamin B12, vitamin B6 and homocysteine: impact on pregnancy outcome

Good clinical practice recommends folic acid supplementation 1 month prior to pregnancy and during the first trimester to prevent congenital malformations. However, high rates of fetal growth and development in later pregnancy may increase the demand for folate. Folate and vitamins B12 and B6 are required for DNA synthesis and cell growth, and are involved in homocysteine metabolism. The primary aim of this study was to determine if maternal folate, vitamin B12, vitamin B6 and homocysteine concentrations at 18-20 weeks gestation are associated with subsequent adverse pregnancy outcomes, including pre-eclampsia and intrauterine growth restriction (IUGR). The secondary aim was to investigate maternal B vitamin concentrations with DNA damage markers in maternal lymphocytes. A prospective observational study was conducted at the Women's and Children's Hospital, Adelaide, South Australia. One hundred and thirty-seven subjects were identified prior to 20 weeks gestation as at high or low risk for subsequent adverse pregnancy outcome by senior obstetricians. Clinical status, dietary information, circulating micronutrients and genome damage biomarkers were assessed at 18-20 weeks gestation. Women who developed IUGR had reduced red blood cell (RBC) folate (P < 0.001) and increased plasma homocysteine concentrations (P < 0.001) compared with controls. Maternal DNA damage, represented by micronucleus frequency and nucleoplasmic bridges in lymphocytes, was positively correlated with homocysteine (r = 0.179, P = 0.038 and r = 0.171, P = 0.047, respectively). Multivariate regression analysis revealed RBC folate was a strong predictor of IUGR (P = 0.006). This study suggests that low maternal RBC folate and high homocysteine values in mid pregnancy are associated with subsequent reduced fetal growth.

Homocysteine: a biomarker in neurodegenerative diseases

Diseases of the central nervous system are found in patients with severe hyperhomocysteinemia (HHcy). Epidemiological studies show a positive, dose-dependent relationship between mild-to-moderate increases in plasma total homocysteine concentrations (Hcy) and the risk of neurodegenerative diseases, such as Alzheimer's disease, vascular dementia, cognitive impairment or stroke. HHcy is a surrogate marker for B vitamin deficiency (folate, B12, B6) and a neurotoxic agent. The concept of improving the patient's clinical outcome by lowering of Hcy with B vitamins seems to be attractive. Recent B vitamin supplementation trials demonstrated a slowing of brain atrophy and improvement in some domains of cognitive function. Meta-analysis of secondary prevention trials showed that B vitamins supplementation caused a decrease in plasma Hcy and a trend for lowering the risk of stroke. HHcy is common in elderly people. Therefore, it seems prudent to identify B vitamin deficient subjects and to ensure sufficient vitamin intake. Therefore, recent evidence supports the role of Hcy as a potential biomarker in age-related neurodegenerative diseases.

Role of vitamin B(12), folate, and thyroid stimulating hormone in dementia: A hospital-based study in north Indian population

Background:

Vitamin B₁₂ and folate represent modifiable risk factors for dementia. They may increase the risk of Alzheimer′s dementia (AD) and vascular dementia (VaD) as their deficiency can increase the homocysteine level due to slowed methylation reaction. Homocysteine has a neurotoxic effect that could lead to neurologic disturbances. Hence, it is important to explore the status of serum B₁₂ and folate in AD and VaD to evolve the treatment strategies for the same.

Objectives:

A retrospective study was conducted to assess the levels of vitamin B₁₂, folate, and thyroid stimulating hormone (TSH) in serum and the relationship of these factors, including age and sex to cognitive decline in VaD, AD, and dementia due to other causes (DOC).

Materials and Methods:

Serum vitamin B₁₂, folate, TSH, and total cholesterol were studied in 32 AD patients (mean age: 65 years), 12 VaD patients (mean age: 61 years), 83 DOC (mean age: 65 years), and 127 control subjects (mean age: 49 years). Results: In AD, VaD, and DOC, the levels of vitamin B₁₂ and folate were significantly lower (P < 0.002; 0.026; 0.002 for vitamin B₁₂ and P < 0.000 in all the 3 groups for folate) as compared with the controls. Similarly, TSH levels were significantly lower in AD and DOC (P < 0.008; 0.038) as compared with the controls.

Conclusion:

Vitamin B₁₂ and folate were significantly low in both AD and VaD patients. Hence, B vitamin supplementation should be considered as possible targets for the therapeutic intervention in dementia.

Epigenetic mechanisms in Alzheimer's disease

Epigenetic modifications help orchestrate sweeping developmental, aging, and disease-causing changes in phenotype by altering transcriptional activity in multiple genes spanning multiple biologic pathways. Although previous epigenetic research has focused primarily on dividing cells, particularly in cancer, recent studies have shown rapid, dynamic, and persistent epigenetic modifications in neurons that have significant neuroendocrine, neurophysiologic, and neurodegenerative consequences. Here, we provide a review of the major mechanisms for epigenetic modification and how they are reportedly altered in aging and Alzheimer's disease (AD). Because of their reach across the genome, epigenetic mechanisms may provide a unique integrative framework for the pathologic diversity and complexity of AD.

The metabolic burden of creatine synthesis

Creatine synthesis is required in adult animals to replace creatine that is spontaneously converted to creatinine and excreted in the urine. Additionally, in growing animals it is necessary to provide creatine to the expanding tissue mass. Creatine synthesis requires three amino acids: glycine, methionine and arginine, and three enzymes: L-arginine:glycine amidinotransferase (AGAT), methionine adenosyltransferase (MAT) and guanidinoacetate methyltransferase (GAMT). The entire glycine molecule is consumed in creatine synthesis but only the methyl and amidino groups, respectively, from methionine and arginine. Creatinine loss averages approximately 2 g (14.6 mmol) for 70 kg males in the 20- to 39-year age group. Creatinine loss is lower in females and in older age groups because of lower muscle mass. Approximately half of this creatine lost to creatinine can be replaced, in omnivorous individuals, by dietary creatine. However, since dietary creatine is only provided in animal products, principally in meat and fish, virtually all of the creatine loss in vegetarians must be replaced via endogenous synthesis. Creatine synthesis does not appear to place a major burden on glycine metabolism in adults since this amino acid is readily synthesized. However, creatine synthesis does account for approximately 40% of all of the labile methyl groups provided by S-adenosylmethionine (SAM) and, as such, places an appreciable burden on the provision of such methyl groups, either from the diet or via de novo methylneogenesis. Creatine synthesis consumes some 20-30% of arginine's amidino groups, whether provided in the diet or synthesized within the body. Creatine synthesis is, therefore, a quantitatively major pathway in amino acid metabolism and imposes an appreciable burden on the metabolism of methionine and of arginine.

The annexin A2 system and vascular homeostasis

Optimal fibrin balance requires precisely controlled plasmin generation on the surface of endothelial cells, which line the blood vessel wall. As a co-receptor for plasminogen and tissue plasminogen activator (tPA), which are key factors in plasmin generation, the annexin A2 (A2) complex promotes vascular fibrinolysis. The intracellular A2 complex is a heterotetramer of two A2 monomers and two copies of the associated protein, p11. In response to endothelial cell activation, A2 is phosphorylated by src-kinase, and translocated to the cell surface in a highly regulated manner. Over-expression of A2 is seen in acute promyelocytic leukemia during the early hemorrhagic phase, while high titer antibodies to A2, as in antiphospholipid syndrome or cerebral venous thrombosis, are associated with thrombosis. In experimental hyperhomocysteinemia, moreover, derivatization of A2 by homocysteine leads to intravascular fibrin accumulation and dysangiogenesis, features that phenocopy the Anxa2(-/-) mouse. Exogenous A2 may also offer a novel therapeutic approach to ischemic thrombotic stroke, as administration of A2 in conjunction with conventional tPA-based thrombolytic therapy improved outcome in an animal model. Here, we discuss the role of the A2 system in vascular homeostasis, the molecular interactions that regulate its profibrinolytic activity, and its potential role in the pathogenesis and treatment of vascular disease.

Cobalamin C defect: natural history, pathophysiology, and treatment

Cobalamin C (Cbl-C) defect is the most common inborn cobalamin metabolism error; it causes impaired conversion of dietary vitamin B12 into its two metabolically active forms, methylcobalamin and adenosylcobalamin. Cbl-C defect causes the accumulation of methylmalonic acid and homocysteine and decreased methionine synthesis. The gene responsible for the Cbl-C defect has been recently identified, and more than 40 mutations have been reported. MMACHC gene is located on chromosome 1p and catalyzes the reductive decyanation of CNCbl. Cbl-C patients present with a heterogeneous clinical picture and, based on their age at onset, can be categorized into two distinct clinical forms. Early-onset patients, presenting symptoms within the first year, show a multisystem disease with severe neurological, ocular, haematological, renal, gastrointestinal, cardiac, and pulmonary manifestations. Late-onset patients present a milder clinical phenotype with acute or slowly progressive neurological symptoms and behavioral disturbances. To improve clinical course and metabolic abnormalities, treatment of Cbl-C defect usually consists of a combined approach that utilizes vitamin B12 to increase intracellular cobalamin and to maximize deficient enzyme activities, betaine to provide a substrate for the conversion of homocysteine into methionine through betaine-homocysteine methyltransferase, and folic acid to enhance remethylation pathway. No proven efficacy has been demonstrated for carnitine and dietary protein restriction. Despite these measures, the long-term follow-up is unsatisfactory especially in patients with early onset, with frequent progression of neurological and ocular impairment. The unfavorable outcome suggests that better understanding of the pathophysiology of the disease is needed to improve treatment protocols and to develop new therapeutic approaches.

Homocysteine-lowering by B vitamins slows the rate of accelerated brain atrophy in mild cognitive impairment: a randomized controlled trial

Background

An increased rate of brain atrophy is often observed in older subjects, in particular those who suffer from cognitive decline. Homocysteine is a risk factor for brain atrophy, cognitive impairment and dementia. Plasma concentrations of homocysteine can be lowered by dietary administration of B vitamins.

Objective

To determine whether supplementation with B vitamins that lower levels of plasma total homocysteine can slow the rate of brain atrophy in subjects with mild cognitive impairment in a randomised controlled trial (VITACOG, ISRCTN 94410159).

Methods and Findings

Single-center, randomized, double-blind controlled trial of high-dose folic acid, vitamins B₆ and B₁₂ in 271 individuals (of 646 screened) over 70 y old with mild cognitive impairment. A subset (187) volunteered to have cranial MRI scans at the start and finish of the study. Participants were randomly assigned to two groups of equal size, one treated with folic acid (0.8 mg/d), vitamin B₁₂ (0.5 mg/d) and vitamin B₆ (20 mg/d), the other with placebo; treatment was for 24 months. The main outcome measure was the change in the rate of atrophy of the whole brain assessed by serial volumetric MRI scans.

Results

A total of 168 participants (85 in active treatment group; 83 receiving placebo) completed the MRI section of the trial. The mean rate of brain atrophy per year was 0.76% [95% CI, 0.63–0.90] in the active treatment group and 1.08% [0.94–1.22] in the placebo group (P = 0.001). The treatment response was related to baseline homocysteine levels: the rate of atrophy in participants with homocysteine >13 µmol/L was 53% lower in the active treatment group (P = 0.001). A greater rate of atrophy was associated with a lower final cognitive test scores. There was no difference in serious adverse events according to treatment category.

Conclusions and Significance

The accelerated rate of brain atrophy in elderly with mild cognitive impairment can be slowed by treatment with homocysteine-lowering B vitamins. Sixteen percent of those over 70 y old have mild cognitive impairment and half of these develop Alzheimer's disease. Since accelerated brain atrophy is a characteristic of subjects with mild cognitive impairment who convert to Alzheimer's disease, trials are needed to see if the same treatment will delay the development of Alzheimer's disease.

Trial Registration

Controlled-Trials.com ISRCTN94410159

Cognitive performance among the elderly in relation to the intake of plant foods. The Hordaland Health Study

Fruits and vegetables are among the most nutritious and healthy of foods, and are related to the prevention of many chronic diseases. The aim of the study was to examine the relationship between intake of different plant foods and cognitive performance in elderly individuals in a cross-sectional study. Two thousand and thirty-one elderly subjects (aged 70-74 years; 55% women) recruited from the general population in Western Norway underwent extensive cognitive testing and completed a comprehensive FFQ. The cognitive test battery covered several domains (Kendrick Object Learning Test, Trail Making Test--part A, modified versions of the Digit Symbol Test, Block Design, Mini-Mental State Examination and Controlled Oral Word Association Test). A validated and self-reported FFQ was used to assess habitual food intake. Subjects with intakes of >10th percentile of fruits, vegetables, grain products and mushrooms performed significantly better in cognitive tests than those with very low or no intake. The associations were strongest between cognition and the combined intake of fruits and vegetables, with a marked dose-dependent relationship up to about 500 g/d. The dose-related increase of intakes of grain products and potatoes reached a plateau at about 100-150 g/d, levelling off or decreasing thereafter, whereas the associations were linear for mushrooms. For individual plant foods, the positive cognitive associations of carrots, cruciferous vegetables, citrus fruits and high-fibre bread were most pronounced. The only negative cognitive association was with increased intake of white bread. In the elderly, a diet rich in plant foods is associated with better performance in several cognitive abilities in a dose-dependent manner.

Subtypes based on cerebrospinal fluid and magnetic resonance imaging markers in normal elderly predict cognitive decline

Cerebrospinal fluid (CSF) and structural magnetic resonance imaging (MRI) show patterns of change in Alzheimer's disease (AD) that precede dementia. The Alzheimer's Disease Neuroimaging Initiative (ADNI) studied normal controls (NC), subjects with mild cognitive impairment (MCI), and subjects with AD to identify patterns of biomarkers to aid in early diagnosis and effective treatment of AD. Two hundred twenty-two NC underwent baseline MRI and clinical examination at baseline and at least one follow-up. One hundred twelve also provided CSF at baseline. Unsupervised clustering based on initial CSF and MRI measures was used to identify clusters of participants with similar profiles. Repeated measures regression modeling assessed the relationship of individual measures, and of cluster membership, to cognitive change over 3 years. Most individuals showed little cognitive change. Individual biomarkers had limited predictive value for cognitive decline, but membership in the cluster with the most extreme profile was associated with more rapid decline in ADAS-cog. Subtypes among NC based on multiple biomarkers may represent the earliest stages of subclinical cognitive decline and AD.

Effect of physiological doses of oral vitamin B12 on plasma homocysteine: a randomized, placebo-controlled, double-blind trial in India

BACKGROUND/OBJECTIVES

Vitamin B(12) (B(12)) deficiency is common in Indians and a major contributor to hyperhomocysteinemia, which may influence fetal growth, risk of type II diabetes and cardiovascular disease. The purpose of this paper was to study the effect of physiological doses of B(12) and folic acid on plasma total homocysteine (tHcy) concentration.

SUBJECTS/METHODS

A cluster randomized, placebo-controlled, double-blind, 2 x 3 factorial trial, using the family as the randomization unit. B(12) was given as 2 or 10 microg capsules, with or without 200 microg folic acid, forming six groups (B(0)F(0), B(2)F(0), B(10)F(0), B(0)F(200), B(2)F(200) and B(10)F(200)). Plasma tHcy concentration was measured before and after 4 and 12 months of supplementation.

RESULTS

From 119 families in the Pune Maternal Nutrition Study, 300 individuals were randomized. There was no interaction between B(12) and folic acid (P=0.14) in relation to tHcy concentration change and their effects were analyzed separately: B(0) vs. B(2) vs. B(10); and F(0) vs. F(200). At 12 months, tHcy concentration reduced by a mean 5.9 (95% CI: -7.8, -4.1) micromol/l in B(2), and by 7.1 (95% CI: -8.9, -5.4) micromol/l in B(10), compared to nonsignificant rise of 1.2 (95% CI: -0.5, 2.9) micromol/l in B(0). B(2) and B(10) did not differ significantly. In F(200), tHcy concentration decreased by 4.8 (95% CI: -6.3, -3.3) micromol/l compared to 2.8 (95% CI: -4.3, -1.2) micromol/l in F(0).

CONCLUSION

Daily oral supplementation with physiological doses of B(12) is an effective community intervention to reduce tHcy. Folic acid (200 microg per day) showed no additional benefit, neither had any unfavorable effects.

Homocysteine as a predictor of cognitive decline in Alzheimer's disease

OBJECTIVE

Moderately elevated levels of plasma total homocysteine are associated with an increased risk of developing Alzheimer's disease. We have tested whether baseline concentrations of homocysteine relate to the subsequent rate of cognitive decline in patients with established Alzheimer's disease (AD).

METHODS

In 97 patients with AD, 73 pathologically-confirmed, we analysed the decline of global cognitive test scores (CAMCOG) over time from the first assessment for at least three 6-monthly visits up to a maximum of 9.5 years (in total 689 assessments). Non-linear mixed-effects statistical models were used.

RESULTS

Baseline homocysteine levels showed a concentration-response relationship with the subsequent rate of decline in CAMCOG scores: the higher the homocysteine, the faster the decline. The relationship was significant in patients aged < 75 years who had not suffered a prior stroke. For example, in patients aged 65 years with a baseline homocysteine of 14 micromol/L, the decline from a CAMCOG score of 88 to a score of 44 occurred 19.2 (95% CI 6.8, 31.6) months earlier than in patients with a baseline homocysteine of 10 micromol/L.

CONCLUSIONS

Raised homocysteine concentrations within the normal range among the elderly strongly relate to the rate of global cognitive decline in patients with Alzheimer disease. Plasma homocysteine can readily be lowered by B-vitamin treatment and trials should be carried out to see if such treatments can slow the rate of cognitive decline in relatively young patients with Alzheimer disease.

Vitamin B12 and older adults

PURPOSE OF REVIEW

To review the prevalence, causes and functional significance of vitamin B12 deficiency in vulnerable subpopulations including older adults and the developing embryo.

RECENT FINDINGS

It is becoming increasingly recognized that the susceptibility to vitamin B12 deficiency may change throughout the life cycle, with the developing embryo and older adults exhibiting elevated risk. Recent data implicate low vitamin B12 status as a risk factor for birth defects resulting from improper neural tube development. The potential for vitamin supplementation and/or food fortification to ameliorate the risk of deficiency in these subpopulations is discussed.

SUMMARY

The prevalence and impact of vitamin B12 deficiency varies throughout the life cycle, with older adults and potentially the developing embryo having the greatest risk and susceptibility. Additional research is needed to develop effective public health interventions that address the unique causes of this nutritional deficiency, which differ among at-risk subpopulations.

L-methylfolate, methylcobalamin, and N-acetylcysteine in the treatment of Alzheimer's disease-related cognitive decline

Neuroinflammatory oxidative stress occurs early in AD pathology. Elevated blood Hcy is a useful marker for such neuroinflammation. Hcy contributes to pathological cascades involving AP and NFTs. In AD, Hcy should be lowered by B-vitamin supplements and NAC.

Homocysteine inhibits neoangiogenesis in mice through blockade of annexin A2-dependent fibrinolysis

When plasma levels of homocysteine (HC), a thiol amino acid formed upon methionine demethylation, exceed 12 muM, individuals are at increased risk of developing large vessel atherothrombosis and small vessel dysfunction. The annexin A2 complex (termed "A2") is the cell surface coreceptor for plasminogen and TPA and accelerates the catalytic activation of plasmin, the major fibrinolytic agent in mammals. We previously showed that HC prevents A2-mediated, TPA-dependent activation of plasminogen in vitro by disulfide derivatization of the "tail" domain of A2. We also demonstrated that fibrinolysis and angiogenesis are severely impaired in A2-deficient mice. We now report here that, although hyperhomocysteinemic mice had a normal coagulation profile and normal platelet function, fibrin accumulated in their tissues due to reduced perivascular fibrinolytic activity and angiogenesis was impaired. A2 isolated from hyperhomocysteinemic mice failed to fully support TPA-dependent plasmin activation. However, infusion of hyperhomocysteinemic mice with fresh recombinant A2, which localized to neoangiogenic endothelial cells, resulted in normalization of angiogenesis and disappearance of peri- and intravascular fibrin. We therefore conclude that hyperhomocysteinemia impairs postnatal angiogenesis by derivatizing A2, preventing perivascular fibrinolysis, and inhibiting directed endothelial cell migration. These findings provide a mechanistic explanation for microvascular dysfunction and macrovascular occlusion in individuals with hyperhomocysteinemia.

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.

Replication by the Epistasis Project of the interaction between the genes for IL-6 and IL-10 in the risk of Alzheimer's disease

Background

Chronic inflammation is a characteristic of Alzheimer's disease (AD). An interaction associated with the risk of AD has been reported between polymorphisms in the regulatory regions of the genes for the pro-inflammatory cytokine, interleukin-6 (IL-6, gene: IL6), and the anti-inflammatory cytokine, interleukin-10 (IL-10, gene: IL10).

Methods

We examined this interaction in the Epistasis Project, a collaboration of 7 AD research groups, contributing DNA samples from 1,757 cases of AD and 6,295 controls.

Results

We replicated the interaction. For IL6 rs2069837 AA × IL10 rs1800871 CC, the synergy factor (SF) was 1.63 (95% confidence interval: 1.10–2.41, p = 0.01), controlling for centre, age, gender and apolipoprotein E ε4 (APOEε4) genotype. Our results are consistent between North Europe (SF = 1.7, p = 0.03) and North Spain (SF = 2.0, p = 0.09). Further replication may require a meta-analysis. However, association due to linkage disequilibrium with other polymorphisms in the regulatory regions of these genes cannot be excluded.

Conclusion

We suggest that dysregulation of both IL-6 and IL-10 in some elderly people, due in part to genetic variations in the two genes, contributes to the development of AD. Thus, inflammation facilitates the onset of sporadic AD.

Acute homocysteine administration impairs memory consolidation on inhibitory avoidance task and decreases hippocampal brain-derived neurotrophic factor immunocontent: prevention by folic acid treatment

In the present study, we first investigated the effect of single homocysteine administration on consolidation of short- and long-term memories of inhibitory avoidance task in Wistar rats. We also measured brain-derived neurotrophic factor levels in the hippocampus and parietal cortex of rats. The influence of pretreatment with folic acid on behavioral and biochemical effects elicited by homocysteine was also studied. Wistar rats were subjected to a folic acid or saline pretreatment from their 22(nd) to 28(th) day of life; 12 h later they were submitted to a single administration of homocysteine or saline. For motor activity and memory evaluation we performed open-field and inhibitory avoidance tasks. Hippocampus and parietal cortex were obtained for brain-derived neurotrophic factor immunocontent determination. Results showed that homocysteine impaired short- and long-term memories and reduced brain-derived neurotrophic factor levels in the hippocampus. Pretreatment with folic acid prevented both the memory deficit and the reduction in the brain-derived neurotrophic factor immunocontent induced by homocysteine injection. Further studies are required to determine the entire mechanism by which folic acid acts and its potential therapeutic use for memory impairment prevention in homocystinuric patients.

Complementary and alternative medicine use for treatment and prevention of late-life mood and cognitive disorders

Late-life mood disorders and cognitive aging are the most common reasons for using complementary and alternative therapies. The amount of rigorous scientific data to support the efficacy of complementary therapies in the treatment of depression or cognitive impairment is extremely limited. The areas with the most evidence for beneficial effects are exercise, herbal therapy (Hypericum perforatum), the use of fish oil, and, to a lesser extent, acupuncture and relaxation therapies. There is a need for further research involving randomized, controlled trials to investigate the efficacy of complementary and alternative therapies in the treatment of depression and cognitive impairment in late-life. This research may lead to the development of effective treatment and preventive approaches for these serious conditions.

Vitamin B-12 and cognition in the elderly

Vitamin B-12 deficiency is often associated with cognitive deficits. Here we review evidence that cognition in the elderly may also be adversely affected at concentrations of vitamin B-12 above the traditional cutoffs for deficiency. By using markers such as holotranscobalamin and methylmalonic acid, it has been found that cognition is associated with vitamin B-12 status across the normal range. Possible mediators of this relation include brain atrophy and white matter damage, both of which are associated with low vitamin B-12 status. Intervention trials have not been adequately designed to test whether these associations are causal. Pending the outcome of better trials, it is suggested that the elderly in particular should be encouraged to maintain a good, rather than just an adequate, vitamin B-12 status by dietary means.

Intake of flavonoid-rich wine, tea, and chocolate by elderly men and women is associated with better cognitive test performance

In a cross-sectional study, we examined the relation between intake of 3 common foodstuffs that contain flavonoids (chocolate, wine, and tea) and cognitive performance. 2031 participants (70-74 y, 55% women) recruited from the population-based Hordaland Health Study in Norway underwent cognitive testing. A cognitive test battery included the Kendrick Object Learning Test, Trail Making Test, part A (TMT-A), modified versions of the Digit Symbol Test, Block Design, Mini-Mental State Examination, and Controlled Oral Word Association Test. Poor cognitive performance was defined as a score in the highest decile for the TMT-A and in the lowest decile for all other tests. A self-reported FFQ was used to assess habitual food intake. Participants who consumed chocolate, wine, or tea had significantly better mean test scores and lower prevalence of poor cognitive performance than those who did not. Participants who consumed all 3 studied items had the best test scores and the lowest risks for poor test performance. The associations between intake of these foodstuffs and cognition were dose dependent, with maximum effect at intakes of approximately 10 g/d for chocolate and approximately 75-100 mL/d for wine, but approximately linear for tea. Most cognitive functions tested were influenced by intake of these 3 foodstuffs. The effect was most pronounced for wine and modestly weaker for chocolate intake. Thus, in the elderly, a diet high in some flavonoid-rich foods is associated with better performance in several cognitive abilities in a dose-dependent manner.

Folic acid with or without vitamin B12 for the prevention and treatment of healthy elderly and demented people

BACKGROUND

Folate deficiency can result in congenital neural tube defects and megaloblastic anaemia. Low folate levels may be due to insufficient dietary intake or inefficient absorption, but impaired metabolic utilization also occurs.Because B12 deficiency can produce a similar anaemia to folate deficiency, there is a risk that folate supplementation can delay the diagnosis of B12 deficiency, which can cause irreversible neurological damage. Folic acid supplements may sometimes therefore include vitamin B12 supplements with simultaneous administration of vitamin B12.Lesser degrees of folate inadequacy are associated with high blood levels of the amino acid homocysteine which has been linked with the risk of arterial disease, dementia and Alzheimer's disease. There is therefore interest in whether dietary supplementation can improve cognitive function in the elderly.However, any apparent benefit from folic acid which was given in combination with B12 needs to be "corrected" for any effect of vitamin B12 alone. A separate Cochrane review of vitamin B12 and cognitive function has therefore been published.

OBJECTIVES

To examine the effects of folic acid supplementation, with or without vitamin B12, on elderly healthy or demented people, in preventing cognitive impairment or retarding its progress.

SEARCH STRATEGY

Trials were identified from a search of the Cochrane Dementia and Cognitive Improvement Group's Specialized Register on 10 October 2007 using the terms: folic acid, folate, vitamin B9, leucovorin, methyltetrahydrofolate, vitamin B12, cobalamin and cyanocobalamin. This Register contains references from all major health care databases and many ongoing trials databases. In addition MEDLINE, EMBASE, CINAHL, PsychINFO and LILACS were searched (years 2003-2007) for additional trials of folate with or without vitamin B12 on healthy elderly people.

SELECTION CRITERIA

All double-blind, placebo-controlled, randomized trials, in which supplements of folic acid with or without vitamin B12 were compared with placebo for elderly healthy people or people with any type of dementia or cognitive impairment.

DATA COLLECTION AND ANALYSIS

The reviewers independently applied the selection criteria and assessed study quality. One reviewer extracted and analysed the data. In comparing intervention with placebo, weighted mean differences and standardized mean difference or odds ratios were estimated.

MAIN RESULTS

Eight randomized controlled trials fulfilled the inclusion criteria for this review. Four trials enrolled healthy older people, and four recruited participants with mild to moderate cognitive impairment or dementia with or without diagnosed folate deficiency. Pooling the data was not possible owing to heterogeneity in sample selections, outcomes, trial duration, and dosage. Two studies involved a combination of folic acid and vitamin B12.There is no adequate evidence of benefit from folic acid supplementation with or without vitamin B12 on cognitive function and mood of unselected healthy elderly people. However, in one trial enrolling a selected group of healthy elderly people with high homocysteine levels, 800 mcg/day folic acid supplementation over three years was associated with significant benefit in terms of global functioning (WMD 0.05, 95% CI 0.004 to 0.096, P = 0.033); memory storage (WMD 0.14, 95% CI 0.04 to 0.24, P = 0.006) and information-processing speed (WMD 0.09, 95% CI 0.02 to 0.16, P = 0.016).Four trials involved people with cognitive impairment. In one pilot trial enrolling people with Alzheimer's disease, the overall response to cholinesterase inhibitors significantly improved with folic acid at a dose of 1mg/day (odds ratio: 4.06, 95% CI 1.22 to 13.53; P = 0.02) and there was a significant improvement in scores on the Instrumental Activities of Daily Living and the Social Behaviour subscale of the Nurse's Observation Scale for Geriatric Patients (WMD 4.01, 95% CI 0.50 to 7.52, P = 0.02). Other trials involving people with cognitive impairment did not show any benefit in measures of cognitive function from folic acid, with or without vitamin B12.Folic acid plus vitamin B12 was effective in reducing serum homocysteine concentrations (WMD -5.90, 95% CI -8.43 to -3.37, P < 0.00001). Folic acid was well tolerated and no adverse effects were reported.

AUTHORS' CONCLUSIONS

The small number of studies which have been done provide no consistent evidence either way that folic acid, with or without vitamin B12, has a beneficial effect on cognitive function of unselected healthy or cognitively impaired older people. In a preliminary study, folic acid was associated with improvement in the response of people with Alzheimer's disease to cholinesterase inhibitors. In another, long-term use appeared to improve the cognitive function of healthy older people with high homocysteine levels. More studies are needed on this important issue.