Vitamin D and Alzheimer's disease: is there a link?

Vitamin D alleviates cognitive dysfunction and brain damage induced by copper sulfate intake in experimental rats: focus on its combination with donepezil

This study aimed to demonstrate the potential benefits of donepezil (DPZ) and vitamin D (Vit D) in combination to counteract the neurodegenerative disorders induced by CuSO4 intake in experimental rats. Neurodegeneration (Alzheimer-like) was induced in twenty-four male Wistar albino rats by CuSO4 supplement to drinking water (10 mg/L) for 14 weeks. AD rats were divided into four groups: untreated AD group (Cu-AD) and three treated AD groups; orally treated for 4 weeks with either DPZ (10 mg/kg/day), Vit D (500 IU/kg/day), or DPZ + Vit D starting from the 10th week of CuSO4 intake. Another six rats were used as normal control (NC) group. The hippocampal tissue content of β-amyloid precursor protein cleaving enzyme 1 (BACE1), phosphorylated Tau (p-tau), clusterin (CLU), tumor necrosis factor-α (TNF-α), caspase-9 (CAS-9), Bax, and Bcl-2 and the cortical content of acetylcholine (Ach), acetylcholinesterase (AChE), total antioxidant capacity (TAC), and malondialdehyde (MDA) were measured. Cognitive function tests (Y-maze) and histopathology studies (hematoxylin and eosin and Congo red stains) and immunohistochemistry for neurofilament. Vit D supplementation alleviated CuSO4-induced memory deficits including significant reduction hippocampal BACE1, p-tau, CLU, CAS-9, Bax, and TNF-α and cortical AChE and MDA. Vit D remarkably increased cortical Ach, TAC, and hippocampal Bcl-2. It also improved neurobehavioral and histological abnormalities. The effects attained by Vit D treatment were better than those attained by DPZ. Furthermore, Vit D boosted the therapeutic potential of DPZ in almost all AD associated behavioral and pathological changes. Vit D is suggested as a potential therapy to retard neurodegeneration.

Association between vitamin D deficiency and multiple sclerosis- MRI significance: A scoping review

Background/Objective

Multiple Sclerosis is a common demyelinating disease of the central nervous system. Several studies suggested a link between vitamin D deficiency and multiple sclerosis disease activity, which can be evaluated by magnetic resonance imaging. Thereby, the main objective of the following scoping review is to summarize the magnetic resonance imaging findings assessing the probable effects of vitamin D on MS disease activity.

Methodology

PRISMA checklist for systematic reviews and meta-analyses was employed to structure this review. Literature was searched for observational and clinical studies tackling the given matter using several search engines including PubMed, CORE, and Embase. Data was extracted in a systematic manner, and the articles meeting the inclusion criteria were quality-assessed by Jadad scale for randomized clinical trials (RCTs) and Newcastle-Ottawa scale for observational studies.

Results

A total of 35 articles were included. Twenty-one (60%) studies noted a statistically significant association between vitamin D and Multiple Sclerosis MRI-detected disease activity. MRI-detected features involved lower contrast-enhancing T1 lesions, lower hyperintense T2 lesions, and a decrease in lesions volume. On the other hand, 40% (14 articles) of the articles did not detect any significant effect of vitamin D on Multiple Sclerosis disease activity. Due to the heterogeneity of the studies involved, meta-analysis was not employed in the given review.

Discussion/conclusion

There was an abundance in the number of research studies investigating the relationship between vitamin D and Multiple Sclerosis while highlighting the significant role of MRI in assessing the activity of the disease. Numerous studies found that higher serum vitamin D levels are associated with decreased new active cortical and subcortical lesions and lower lesions volume. These findings highlight the importance of imaging modalities in the various aspects of neurological diseases and encourage further research to focus on the preventive effects of vitamin D on MS patients.

Diet Associated with Inflammation and Alzheimer's Disease

Neurocognitive disorders, such as Alzheimer's disease (AD), affect millions of people worldwide and are characterized by cognitive decline. Human and animal studies have shown that chronic immune response and inflammation are important factors in the pathogenesis of AD. Chronic inflammation can accelerate the aggregation of amyloid-β peptides and later hyperphosphorylation of tau proteins. The exact etiology of AD is not clear, but genetics and environmental factors, such as age, family history, and lifestyle are linked to neurodegenerative diseases. Lifestyle habits, such as poor diet, are associated with inflammation and could accelerate or slow down the progression of neurodegenerative diseases. Here we provide a review of the potential conditions and factors that stimulate the inflammatory processes in AD. An understanding of inflammatory mechanisms influencing the development of AD may help to protect against dementia and AD.

Association between vitamin D status and cognitive impairment in acute ischemic stroke patients: a prospective cohort study

Objective

Previous studies found that low vitamin D levels were modestly associated with risk of stroke and poor functional outcome after stroke. In addition, vitamin D deficiency has been linked with cognitive decline. Our study aimed to explore the potential relationship between vitamin D levels in the short-term acute phase of ischemic stroke and cognitive impairment at 1 month.

Methods

In total, 354 ischemic stroke patients were consecutively enrolled in the study and received 1-month follow-up. The serum levels of vitamin D were measured within 24 hours after admission. Cognitive function was evaluated by the Mini-Mental State Examination (MMSE) at 1 month after acute ischemic stroke. Cognitive impairment was defined according to different education levels.

Results

According to MMSE scores, 114 participants (32.2%) had cognitive impairment at 1 month. Patients with vitamin D deficiency were more likely to have cognitive impairment than those with vitamin D insufficiency and vitamin D sufficiency (P<0.001). After adjusting for potential confounders in our Cox proportional hazards model, vitamin D deficiency was independently associated with the development of cognitive impairment in acute ischemic stroke patients.

Conclusion

Independent of established risk factors, vitamin D deficiency in the short-term phase of ischemic stroke was associated with a higher incidence of 1-month cognitive impairment.

Vitamin D administration, cognitive function, BBB permeability and neuroinflammatory factors in high-fat diet-induced obese rats

OBJECTIVES

The purpose of this research was to investigate the effects of vitamin D administration on cognitive function, nuclear factor-κB (NF-κB), brain-derived neurotrophic factor (BDNF) concentration in the hippocampus and blood-brain barrier (BBB) permeability in high-fat diet (HFD)-induced obese rats.

METHODS

Male Wistar rats were fed either a control diet or HFD for 16 weeks (n=20); then, each group was randomized into two subgroups supplemented orally with 500 IU kg^-1 vitamin D for 5 weeks. A Morris water maze (MWM) test was performed at the 21st week to examine cognitive function. BBB permeability was characterized by Evans blue dye in the hippocampus. BDNF and NF-κB concentrations in the hippocampus and serum vitamin D concentrations were also measured.

RESULTS

HFD led to a significant delay in escape latency time and reduced time of MWM probe test because of increased NF-κB and decreased BDNF concentrations in the hippocampus. Vitamin D supplementation in the HFD group significantly reduced body weight, NF-κB concentrations, BBB permeability and increased BDNF concentrations in the hippocampus.

CONCLUSIONS

Vitamin D reversed HFD-induced cognitive impairments by reduction of the NF-κB and elevation of BDNF concentrations and modulation of the BBB permeability in rats' hippocampus.

Vitamin D deficiency is associated with increased risk of Alzheimer's disease and dementia: evidence from meta-analysis

Background

In recent years, the associations between vitamin D status and Alzheimer’s disease (AD) and dementia have gained increasing interests. The present meta-analysis was designed to estimate the association between vitamin D deficiency and risk of developing AD and dementia.

Methods

A literature search conducted until February 2015 identified 10 study populations, which were included in the meta-analysis. Pooled risk ratios (RRs) and 95 % confidence interval (CI) were calculated with a random-effect model using Stata software package.

Results

Results of our meta-analysis showed that subjects with deficient vitamin D status (25(OH)D level < 50 nmol/L) were at increased risk of developing AD by 21 % compared with those possessing 25(OH)D level > 50 nmol/L. Similar analysis also found a significantly increased dementia risk in vitamin D deficient subjects. There is no evidence for significant heterogeneity among the included studies.

Conclusion

Available data indicates that lower vitamin D status may be associated with increased risk of developing AD and dementia. More studies are needed to further confirm the associations and to evaluate the beneficial effects of vitamin D supplementation in preventing AD and dementia.

Effect of Vitamin Intake on Cognitive Decline in Older Adults: Evaluation of the Evidence

OBJECTIVES

The objective of this review was to evaluate the evidence from human studies on the intake of vitamins, either as monotherapies or in combination with other vitamins, as neuroprotective agents that may delay the onset of cognitive decline in older adults.

METHODS

Evidence-based methodologies were used to capture and evaluate the highest levels of evidence.

FINDINGS

The current evidence available showed no association for cognitive benefits of vitamins B6 or B12 as a monotherapy, and recent systematic reviews provide no clear evidence that supplementation with vitamin B6, B12 and/or folic acid improves dementia outcomes or slows cognitive decline, even though it may normalise homocysteine levels. Meta-analyses from systematic reviews have shown an association between low vitamin D levels and diminished cognitive function, although causality cannot be confirmed from the available evidence. There is no convincing evidence for an association of vitamin A, vitamin C or vitamin E either as a monotherapy or in combination with other antioxidant vitamins such as β-carotene and the prevention of cognitive decline. The appraisal of nineteen systematic reviews and meta-analyses has highlighted the heterogeneity between studies, and the need for better consensus on definitions of cognitive decline, duration of testing and agreement on which specific endpoints are clinically relevant.

CONCLUSIONS

Evaluation of the totality of the currently available evidence indicates that intake of the above vitamins, either as a monotherapy, or in combination with other vitamins, has no clinically-relevant effect on delaying cognitive decline or delaying the onset of dementia in older adults.

Review: the role of vitamin D in nervous system health and disease

Vitamin D and its metabolites have pleomorphic roles in both nervous system health and disease. Animal models have been paramount in contributing to our knowledge and understanding of the consequences of vitamin D deficiency on brain development and its implications for adult psychiatric and neurological diseases. The conflation of in vitro, ex vivo, and animal model data provide compelling evidence that vitamin D has a crucial role in proliferation, differentiation, neurotrophism, neuroprotection, neurotransmission, and neuroplasticity. Vitamin D exerts its biological function not only by influencing cellular processes directly, but also by influencing gene expression through vitamin D response elements. This review highlights the epidemiological, neuropathological, experimental and molecular genetic evidence implicating vitamin D as a candidate in influencing susceptibility to a number of psychiatric and neurological diseases. The strength of evidence varies for schizophrenia, autism, Parkinson's disease, amyotrophic lateral sclerosis, Alzheimer's disease, and is especially strong for multiple sclerosis.

Circulating biomarkers that predict incident dementia

Dementia is currently diagnosed based on clinical symptoms and signs, but significant brain damage has already occurred by the time a clinical diagnosis of dementia is made, and it is increasingly recognized that this may be too late for any effective intervention. It would therefore be of great public health and preventive value to define a variety of biomarkers that could permit early detection of persons at a higher risk for developing dementia, and specifically dementia due to Alzheimer's disease. Nevertheless, for the purpose of large-scale screening, circulating biomarkers are more appropriate because they are less invasive than lumbar puncture, less costly than brain amyloid imaging and can be easily assessed repeatedly in a primary care clinic setting. In this brief review we will review a number of candidate molecules implicated as possible predictors of dementia risk. These candidates include markers of vascular injury, metabolic and inflammatory states, amyloid and tau pathway markers, measures of neural degeneration and repair efforts, and other molecules that might contribute to anatomical and functional changes characteristic of dementia and Alzheimer's disease.

Plasma protein profiling of Mild Cognitive Impairment and Alzheimer's disease using iTRAQ quantitative proteomics

BACKGROUND

With the promise of disease modifying treatments, there is a need for more specific diagnosis and prognosis of Alzheimer's disease (AD) and mild cognitive impairment (MCI). Plasma biomarkers are likely to be utilised to increase diagnostic accuracy and specificity of AD and cognitive decline.

METHODS

Isobaric tags (iTRAQ) and proteomic methods were used to identify potential plasma biomarkers of MCI and AD. Relative protein expression level changes were quantified in plasma of 411 cognitively normal subjects, 19 AD patients and 261 MCI patients. Plasma was pooled into 4 groups including normal control, AD, amnestic single and multiple domain MCI (aMCI), and nonamnestic single and multiple domain MCI (nMCI). Western-blotting was used to validate iTRAQ data. Integrated function and protein interactions were explored using WEB based bioinformatics tools (DAVID v6.7 and STRING v9.0).

RESULTS

In at least two iTRAQ replicate experiments, 30 proteins were significantly dysregulated in MCI and AD plasma, relative to controls. These proteins included ApoA1, ApoB100, complement C3, C4b-binding protein, afamin, vitamin D-binding protein precursor, isoform 1 of Gelsolin actin regulator, Ig mμ chain C region (IGHM), histidine-rich glycoprotein and fibrinogen β and γ chains. Western-blotting confirmed that afamin was decreased and IGHM was increased in MCI and AD groups. Bioinformatics results indicated that these dysregulated proteins represented a diversity of biological processes, including acute inflammatory response, cholesterol transport and blood coagulation.

CONCLUSION

These findings demonstrate that expression level changes in multiple proteins are observed in MCI and AD plasma. Some of these, such as afamin and IGHM, may be candidate biomarkers for AD and the predementia condition of MCI.

Epilepsy and vitamin D

Several disorders, both systemic and those of the nervous system, have been linked with vitamin D deficiency. Neurological disorders with a vitamin D link include but are not limited to multiple sclerosis, Alzheimer and Parkinson disease, as well as cerebrovascular disorders. Epilepsy which is the second leading neurological disorder received much less attention. We review evidence supporting a link between vitamin D and epilepsy including those coming from ecological as well as interventional and animal studies. We also assess the literature on the interaction between antiepileptic drugs and vitamin D. Converging evidence indicates a role for vitamin D deficiency in the pathophysiology of epilepsy.

Vitamin D levels in Alzheimer's and Parkinson's diseases: a meta-analysis

OBJECTIVE

Recent accumulating evidence shows that vitamin D deficiency is prevalent in individuals with AD and PD. The purpose of the present study is to perform a meta-analysis on the 25-hydroxyvitamin D (25(OH)D) status in this population of patients.

METHODS

We searched all articles in English published up to March 2012 concerning the 25(OH)D level in AD and PD patients. For AD, six studies covering 319 patients and 573 controls were included in the meta-analysis. For PD, five studies discussing 434 patients and 3451 controls were included.

RESULTS

It was found that AD patients had lower levels of 25(OH)D than healthy controls (summary standardized mean difference [SMD], -1.39; 95% confidence interval [CI], -2.79 to 0.01). Similar results were found for PD patients versus healthy controls (summary SMD, -1.33; 95% CI, -2.44 to -0.21).

CONCLUSION

The results indicate that despite the similar mean age between patients and healthy controls in each identified study, both AD and PD patients have lower levels of 25(OH)D than controls.

Vitamin D-binding protein interacts with Aβ and suppresses Aβ-mediated pathology

The level of vitamin D-binding protein (DBP) is increased in the cerebrospinal fluid of patients with Alzheimer's disease (AD), suggesting a relationship with its pathogenesis. In this study, we investigated whether and how DBP is related to AD using several different approaches. A pull-down assay and a surface plasmon resonance binding assay indicated direct interactions between purified DBP and amyloid beta (Aβ), which was confirmed in the brain of AD patients and transgenic AD model mice by immunoprecipitation assay and immunohistochemical double-staining method. Moreover, atomic force microscopic examination revealed that DBP reduced Aβ aggregation in vitro. DBP also prevented Aβ-mediated death in cultured mouse hippocampal HT22 cell line. Finally, DBP decreased Aβ-induced synaptic loss in the hippocampus and rescued memory deficits in mice after injection of Aβ into the lateral ventricle. These results provide converging evidence that DBP attenuates the harmful effects of Aβ by a direct interaction, and suggest that DBP is a promising therapeutic agent for the treatment of AD.

The association between dairy product consumption and cognitive function in the National Health and Nutrition Examination Survey

The present cross-sectional study sought to determine the potential relationships between the intake of dairy foods (total dairy products, milk and cheese) and cognitive function through information garnered in the National Health and Nutrition Examination Surveys (1988-94 and 1999-2002). Cognitive measures of vasomotor speed, coding speed and immediate memory recall were assessed from a simple reaction time task (SRTT), symbol-digit substitution test (SDST) and serial digit learning task, respectively, in adults 20-59 years of age. A summation of the percentile rank scores on each of the three tests provided a measure of overall cognitive function. In adults 60 years of age and above, a story recall test and a digit-symbol substitution test (DSST) were utilised to determine cognitive function in an elderly population. The results indicated that cognitive scores for the SRTT were not different between consumers and non-consumers of dairy foods. However, there were associations observed between 20- and 59-year-old consumers of total dairy foods and a higher SDST percentile score (53.2 (SE 1.3) to 49.4 (SE 2.0)) and a calculated global cognitive percentile score (53.3 (SE 1.1) to 50.2 (SE 1.4)) compared with non-consumers. A similar significant association was observed with cheese consumers. In adults over 60 years of age, an association between total dairy product consumption and higher DSST percentile scores (51.5 (SE 1.9) to 46.2 (se 3.0)) was also observed. These findings highlight the need for additional research on how dairy products may affect cognition and by what mechanisms, through its nutrients or other components.

Alzheimer's disease and risk of hip fracture: a meta-analysis study

Background. Alzheimer's disease (AD) is the most common cause of dementia in the elderly population. Growing evidence supports that AD patients are at high risk for hip fracture, but the issue remains questionable. The purpose of the present study is to perform a meta-analysis to explore the association between AD and risk of hip fracture. Considering that bone mineral density (BMD) acts as a strong predictor of bone fracture, we also studied the hip BMD in AD patients. Methods. We searched all publications in Medline, SciVerse Scopus, and Cochrane Library published up to January 2012 about the association between AD and hip fracture or hip BMD. Results. There are 9 studies included in the meta-analysis. The results indicate that AD patients are at higher risk for hip fracture (OR and 95% CI fixed: ES = 2.58, 95% CI = [2.03, 3.14]; dichotomous data: summary OR = 1.80, 95% CI = [1.54, 2.11]) than healthy controls. Further meta-analysis showed that AD patients have a lower hip BMD (summary SMD = −1.12, 95% CI = [−1.34, −0.90]) than healthy controls. Conclusions. It was found that in comparison with healthy controls AD patients are at higher risk for hip fracture and have lower hip BMD.

The vitamin D receptor gene is associated with Alzheimer's disease

Vitamin D may have a role in brain function. Low levels have been frequently associated with cognitive decline and may contribute to diseases of the nervous system. The vitamin D receptor (VDR) is widely expressed in human brain. Vitamin D appears to be neuroprotective and may regulate inflammation in the brain. We examined two VDR polymorphisms, Apa1 and Taq1. We used DNA from 255 Alzheimer's disease (AD) cases and 260 cognitively screened elderly controls from the longitudinal cohort of the Oxford Project to Investigate Memory and Ageing (OPTIMA). The presence of each of the linked alleles, Apa1 T and Taq1 G, was associated with the risk of AD, particularly in people <75 years old: odds ratios ≥3.0 and p≤0.005. We also found preliminary evidence of interactions associated with AD between these polymorphisms and two other genes involved in the regulation of inflammation, interleukin-10 (IL10) and dopamine β-hydroxylase (DBH): synergy factors ≥3.4, uncorrected p<0.05. These associations are biologically plausible and are consistent with a role for vitamin D in AD. Nevertheless, we consider this to be a hypothesis-generating study, which needs to be replicated in a larger dataset.

Vitamin D, cognitive dysfunction and dementia in older adults

The physiologically active form of vitamin D, 1,25-dihydroxyvitamin D(3), is a fat-soluble steroid hormone with a well established role in skeletal health. A growing body of evidence suggests low vitamin D levels also play a role in the pathogenesis of a wide range of non-skeletal, age-associated diseases including cancer, heart disease, type 2 diabetes mellitus and stroke. Low levels of serum 25-hydroxyvitamin D [25(OH)D], a stable marker of vitamin D status, are also associated with increased odds of prevalent cognitive dysfunction, Alzheimer's disease and all-cause dementia in a number of studies, raising the possibility that vitamin D plays a role in the aetiology of cognitive dysfunction and dementia. To date, the majority of human studies reporting associations between vitamin D and cognition or dementia have been cross-sectional or case-control designs that do not permit us to exclude the possibility that such associations are a result of disease progression rather than being causal. Animal and in vitro experiments have identified a number of neuroprotective mechanisms that might link vitamin D status to cognitive dysfunction and dementia, including vasoprotection and amyloid phagocytosis and clearance, but the clinical relevance of these mechanisms in humans is not currently clear. Two recent, large, prospective studies go some way to establish the temporal relationship with cognitive decline. The relative risk of cognitive decline was 60% higher (relative risk = 1.6, 95% CI 1.2, 2.0) in elderly Italian adults with severely deficient 25(OH)D levels (<25 nmol/L) when compared with those with sufficient levels (≥75 nmol/L). Similarly, the odds of cognitive decline were 41% higher (odds ratio = 1.4, 95% CI 0.9, 2.2) when elderly US men in the lowest quartile (≤49.7 nmol/L) were compared with those in the highest quartile (≥74.4 nmol/L). To our knowledge, no prospective studies have examined the association between 25(OH)D levels and incident dementia or neuroimaging abnormalities. The possible therapeutic benefits of vitamin D have attracted considerable interest as over 1 billion people worldwide are thought to have insufficient 25(OH)D levels and these levels can be increased using inexpensive and well tolerated dietary supplements. However, no large randomized controlled trials have yet examined the effect of vitamin D supplements on cognitive decline or incident dementia. Further studies are urgently needed to establish which mechanisms have clinical relevance in human populations and whether vitamin D supplements are effective at minimizing cognitive decline or preventing dementia.

Widespread vitamin D insufficiency: A new challenge for primary prevention, with particular reference to multiple sclerosis

In the past 10 years, our knowledge of vitamin D has been revolutionized on two main points. Firstly, this vitamin is not only crucial for bone and calcium metabolism but also exerts major hormonal actions via its active metabolite (calcitriol) and specific receptors in almost all organs. The diverse non-classical actions of vitamin D-i.e. anti-inflammatory, immunomodulatory, antiproliferative and as a neurotransmitter-could have protective and preventive effects for a wide variety of pathologies, such as autoimmune diseases, cancer, infections and cardiovascular affections. Secondly, daily vitamin D requirements have been redefined thanks to many recent metabolic and pathological studies and are about 10 times higher than the amount considered sufficient until a few years ago. The fact that sunshine is the essential natural source of vitamin D and is limited in temperate and Nordic countries, coupled with the fact that modern lifestyle increasingly removes people from exposure to the sun, could explain why a great majority of the general population in these countries are in a state of vitamin D insufficiency. A lack of vitamin D can therefore also be observed in all pathologies but it may play a pathogenic role only in some of them. The incrimination of hypovitaminosis D as a risk factor is a reasonable assumption when several different research approaches used in a given pathology have consistently concluded that vitamin D is likely involved in that pathology. In multiple sclerosis, taken here as a prime example, there is a substantial rationale for vitamin D involvement, based on the findings of different experimental, epidemiological, genetic and immunological studies. Possible curative effects of vitamin D, in addition to a preventive action, are currently being tested but have not yet been demonstrated in most pathologies. However, these two questions appear to be clearly distinct and may involve notably different mechanisms. Lastly, since vitamin D insufficiency exists in most people living in mid- or high-latitude countries, vitamin D could exert multiple major preventive actions, simple supplementation is both safe and inexpensive and, for a vitamin-hormone, supplementation seems obligatory from a general preventive medical point of view alone, it follows that vitamin D supplementation should be organized in these countries to treat all those currently in a state of insufficiency, patients and 'normal' subjects alike, without further delay.