Is vitamin D hypothesis for schizophrenia valid? Independent segregation of psychosis in a family with vitamin-D-dependent rickets type IIA

Association of vitamin D and vitamin B12 with cognitive impairment in elderly aged 80 years or older: a cross-sectional study

BACKGROUND

The present study aimed to assess the association of vitamin D and vitamin B₁₂ with cognitive impairment in elderly people.

METHODS

The data were obtained from a cross-sectional study that included individuals aged 80 years or older living in the urban and rural areas of the cities of Siderópolis and Treviso in the state of Santa Catarina, Brazil. In total, 165 elderly people were included in the analysis. The outcome of cognitive decline was assessed by the Mini-Mental State Examination. Vitamin D and vitamin B₁₂ levels were measured from blood samples. The socio-demographic, anthropometric and health variables used in the analysis were collected from a questionnaire. Crude and adjusted analyses of the relationship between vitamins D and B₁₂ and cognitive decline were performed using a Poisson regression model.

RESULTS

The prevalence of cognitive decline was 35.2%. In the adjusted model, individuals who had vitamin D levels >19 ng mL^-1 showed a lower prevalence of cognitive decline (prevalence ratio = 0.59; 95% confidence interval = 0.39-0.87). Those participants who had vitamin B₁₂ levels of ≥496 pg mL^-1 had a higher prevalence of cognitive decline (prevalence ratio = 1.90; 95% confidence interval = 1.08-3.36).

CONCLUSIONS

The present study showed that individuals aged ≥80 years who had vitamin D levels of ≤18 ng mL^-1 had a higher prevalence of cognitive decline even after adjustment for potential confounders. In addition, the study demonstrated that vitamin B₁₂ levels of ≥496 pg mL^-1 in this population were also a risk factor for cognitive decline. A cross-sectional analysis does not enable the inference of a cause-effect relationship and additional studies are needed to understand these relationships.

Nuclear Receptors and Neuroinflammation in Schizophrenia

Introduction

Several nuclear receptor family members have been associated with schizophrenia and inflammation. Vitamins A and D exert anti-inflammatory actions, but their receptors (mainly nuclear receptors) have not been extensively studied in either schizophrenia brains or in association with neuroinflammation. We examined the expression of vitamin A (RARs and RXRs) and vitamin D and protein disulphide-isomerase A3 (PDIA3) receptors, as well as nuclear orphan receptors (NR4As), in the context of elevated cytokine expression in the dorsolateral prefrontal cortex (DLPFC).

Methods

mRNA levels of nuclear receptors were measured in DLPFC tissues via RT-qPCR. ANCOVAs comparing high inflammation schizophrenia, low inflammation schizophrenia and low inflammation control groups were performed.

Results

RARG, RXRB, NR4A1 and NR4A3 transcripts showed significant differential expression across the three groups (ANCOVA p = 0.02-0.001). Post hoc testing revealed significant reductions in RARG expression in schizophrenia with low inflammation compared to schizophrenia with high inflammation and to controls, and RXRB mRNA was significantly reduced in schizophrenia with low inflammation compared to controls. NR4A1 and NR4A3 mRNAs were decreased in schizophrenia with high inflammation compared to schizophrenia with low inflammation, with NR4A1 also significantly different to controls.

Conclusion

In schizophrenia, changes in nuclear receptor mRNA levels involved with mediating actions of vitamin A derivatives vary according to the inflammatory state of brains.

Serum 25-hydroxyvitamin d and the onset of late-life depressive mood in older men and women: the Pro.V.A. study

INTRODUCTION

Biological evidence suggests that vitamin D might be involved in regulating mood. The relationship between 25-hydroxyvitamin D (25OHD) and the onset of depressive symptoms was examined over a 4.4-year follow-up in a sample of older adults.

METHODS

This research was part of the Progetto Veneto Anziani (Pro.V.A.), an Italian population-based cohort study on a total of 1,039 women and 636 men aged 65 and older. Serum 25OHD levels were measured at baseline. Depressive symptoms were assessed with the Geriatric Depression Scale (GDS) at the baseline and during the follow-up. Analyses were adjusted for relevant confounders, including health and performance status.

RESULTS

25OHD levels correlated inversely with baseline GDS scores, but only in women. After controlling for confounders, women deficient in vitamin D (25OHD < 50 nmol/L) had higher GDS scores than those who were replete (25OHD > 75 nmol/L), with mean [SE] GDS scores: 9.57 [0.37] vs 8.31 [0.31], respectively, p = .02. In men, the relationship between 25OHD levels and baseline GDS scores was no longer significant after controlling for covariates. Adjusted hazard ratios and 95% confidence intervals for incident depression in participants who were vitamin D deficient vs replete were not statistically significant (hazard ratio: 0.74, 95% confidence interval [0.47-1.16] in women; hazard ratio: 0.96 95% confidence interval [0.45-2.06] in men).

CONCLUSION

Although an independent inverse association between 25OHD levels and GDS scores emerged for women on cross-sectional analysis, vitamin D deficiency showed no direct effect on the onset of late-life depressive symptoms in our prospectively studied population. Further studies are warranted to clarify the potential influence of vitamin D on psychological health.

Vitamin D, effects on brain development, adult brain function and the links between low levels of vitamin D and neuropsychiatric disease

Increasingly vitamin D deficiency is being associated with a number of psychiatric conditions. In particular for disorders with a developmental basis, such as autistic spectrum disorder and schizophrenia the neurobiological plausibility of this association is strengthened by the preclinical data indicating vitamin D deficiency in early life affects neuronal differentiation, axonal connectivity, dopamine ontogeny and brain structure and function. More recently epidemiological associations have been made between low vitamin D and psychiatric disorders not typically associated with abnormalities in brain development such as depression and Alzheimer's disease. Once again the preclinical findings revealing that vitamin D can regulate catecholamine levels and protect against specific Alzheimer-like pathology increase the plausibility of this link. In this review we have attempted to integrate this clinical epidemiology with potential vitamin D-mediated basic mechanisms. Throughout the review we have highlighted areas where we think future research should focus.

Models of neurodevelopmental abnormalities in schizophrenia

The neurodevelopmental hypothesis of schizophrenia asserts that the underlying pathology of schizophrenia has its roots in brain development and that these brain abnormalities do not manifest themselves until adolescence or early adulthood. Animal models based on developmental manipulations have provided insight into the vulnerability of the developing fetus and the importance of the early environment for normal maturation. These models have provided a wide range of validated approaches to answer questions regarding environmental influences on both neural and behavioral development. In an effort to better understand the developmental hypothesis of schizophrenia, animal models have been developed, which seek to model the etiology and/or the pathophysiology of schizophrenia or specific behaviors associated with the disease. Developmental models specific to schizophrenia have focused on epidemiological risk factors (e.g., prenatal viral insult, birth complications) or more heuristic models aimed at understanding the developmental neuropathology of the disease (e.g., ventral hippocampal lesions). The combined approach of behavioral and neuroanatomical evaluation of these models strengthens their utility in improving our understanding of the pathophysiology of schizophrenia and developing new treatment strategies.

Developmental vitamin D deficiency causes abnormal brain development

There is now clear evidence that vitamin D is involved in brain development. Our group is interested in environmental factors that shape brain development and how this may be relevant to neuropsychiatric diseases including schizophrenia. The origins of schizophrenia are considered developmental. We hypothesised that developmental vitamin D (DVD) deficiency may be the plausible neurobiological explanation for several important epidemiological correlates of schizophrenia namely: (1) the excess winter/spring birth rate, (2) increased incidence of the disease in 2nd generation Afro-Caribbean migrants and (3) increased urban birth rate. Moreover we have published two pieces of direct epidemiological support for this hypothesis in patients. In order to establish the "Biological Plausibility" of this hypothesis we have developed an animal model to study the effect of DVD deficiency on brain development. We do this by removing vitamin D from the diet of female rats prior to breeding. At birth we return all dams to a vitamin D containing diet. Using this procedure we impose a transient, gestational vitamin D deficiency, while maintaining normal calcium levels throughout. The brains of offspring from DVD-deficient dams are characterised by (1) a mild distortion in brain shape, (2) increased lateral ventricle volumes, (3) reduced differentiation and (4) diminished expression of neurotrophic factors. As adults, the alterations in ventricular volume persist and alterations in brain gene and protein expression emerge. Adult DVD-deficient rats also display behavioural sensitivity to agents that induce psychosis (the NMDA antagonist MK-801) and have impairments in attentional processing. In this review we summarise the literature addressing the function of vitamin D on neuronal and non-neuronal cells as well as in vivo results from DVD-deficient animals. Our conclusions from these data are that vitamin D is a plausible biological risk factor for neuropsychiatric disorders and that vitamin D acts as a neurosteroid with direct effects on brain development.

ABNORMAL BEHAVIORAL ORGANIZATION OF GROOMING IN MICE LACKING THE VITAMIN D RECEPTOR GENE

Vitamin D is a steroid hormone with several important functions in the nervous system. Numerous human and animal data link alterations in the vitamin D system to various behavioral disorders. Grooming is an important element of rodent behavior with a general pattern of cephalocaudal progression (paw licking - nose/face wash - body wash - tail/genitals wash). Here we studied whether genetic ablation of vitamin D nuclear receptors (VDR) in mice may be associated with altered behavioral sequencing of grooming. Overall, VDR null mutant mice showed abnormal grooming, including a higher percentage of "incorrect" transitions and longer duration of "incorrect" grooming (contrary to the cephalocaudal progression); a higher percentage of interrupted grooming bouts; and the atypical regional distribution of grooming (more leg grooming, less body and tail/genitals grooming), compared to their wild-type controls. Grooming of heterozygous mice was similar to the wild-type group, indicating that abnormal grooming patterning is inherited as a recessive. In contrast, behavioral sequencing of another complex behavior (mating with a female) was unaltered in all three genotypes, suggesting grooming-specific abnormal sequencing in these mutant mice. Our results suggest that a neurosteroid vitamin D and VDR may play an important role in controlling sequencing of grooming in mice, and further confirm the important role of the vitamin D system and VDR in the regulation of behavior.

Is there convincing biological or behavioral evidence linking vitamin D deficiency to brain dysfunction?

Vitamin D insufficiency is common in the United States; the elderly and African-Americans are at particularly high risk of deficiency. This review, written for a broad scientific readership, presents a critical overview of scientific evidence relevant to a possible causal relationship between vitamin D deficiency and adverse cognitive or behavioral effects. Topics discussed are 1) biological functions of vitamin D relevant to cognition and behavior; 2) studies in humans and rodents that directly examine effects of vitamin D inadequacy on cognition or behavior; and 3) immunomodulatory activity of vitamin D relative to the proinflammatory cytokine theory of cognitive/behavioral dysfunction. We conclude there is ample biological evidence to suggest an important role for vitamin D in brain development and function. However, direct effects of vitamin D inadequacy on cognition/behavior in human or rodent systems appear to be subtle, and in our opinion, the current experimental evidence base does not yet fully satisfy causal criteria. Possible explanations for the apparent inconsistency between results of biological and cognitive/behavioral experiments, as well as suggested areas for further research are discussed. Despite residual uncertainty, recommendations for vitamin D supplementation of at-risk groups, including nursing infants, the elderly, and African-Americans appear warranted to ensure adequacy.

Neurosteroid hormone vitamin D and its utility in clinical nutrition

PURPOSE OF REVIEW

Vitamin D is a seco-steroid hormone with multiple functions in the nervous system. We discuss clinical and experimental evidence of the role of vitamin D in normal and pathological brain functions, and analyze the relative importance of vitamin D-modulated brain mechanisms at different stages of life. We also outline perspectives for the use of vitamin D in clinical nutrition to prevent or treat various brain disorders.

RECENT FINDINGS

Numerous brain dysfunctions are linked to vitamin D deficits and/or dysfunctions of its receptors. In both animals and humans, vitamin D serves as an important endogenous and/or exogenous regulator of neuroprotection, antiepileptic and anticalcification effects, neuro-immunomodulation, interplay with neurotransmitters and hormones, modulation of behaviors, brain ageing, and some other, less-explored, brain processes.

SUMMARY

Vitamin D emerges as an important neurosteroid hormone in the brain, with a strong potential for age-specific applications in clinical nutrition.

Thyroid hormones and retinoids: a possible link between genes and environment in schizophrenia

Phenotypic discordance for schizophrenia in monozygotic twins clearly indicates involvement of environmental factors as key determinants in disease development. Positive findings from genome scans, linkage and association studies apply in only a minority of those affected, while post-mortem brain investigations reveal altered expression of genes and proteins involved in numerous neurodevelopmental, metabolic and neurotransmitter pathways. Such altered expressions could result, on the one hand, from mutations in coding regions or polymorphisms in the promoter and regulatory regions in genes within those areas identified by gene searches or, on the other hand, from inadequate amounts of modulators, transporters and synthesizers of transcription factors necessary for regulation of the putative genes. Hormones and vitamins are such modulators. They could serve as bridges between genes and environment in schizophrenia. Multiple evidence supports the suggestion of retinoids and thyroid hormones as plausible actors in these roles. Both are not only essential for normal development of the central nervous system but also regulate the expression of many neurotransmitters, their synthesizing enzymes and receptors, and other genes in broader signaling transduction cascades affecting pathways that are altered in response to treatment. Functional and positional candidate genes include retinoic acid and thyroid hormone receptors, retinaldehyde dehydrogenases and deiodinases, which synthesize the powerful morphogens, retinoic acid and triiodothyronine, and the enzymes involved in their inactivation. This review highlights selective evidence supporting the retinoid and thyroid hormone hypotheses of schizophrenia.

Behavioural anomalies in mice evoked by “Tokyo” disruption of the Vitamin D receptor gene

Vitamin D is a steroid hormone with many important functions in the brain, mediated through the nuclear Vitamin D receptor (VDR). Mounting clinical data link VDR mutations to various psychiatric phenotypes. We have reported previously that mutant mice lacking functional VDR ("Tokyo" VDR mutant mice) display several behavioural anomalies, including high anxiety and aberrant grooming. Given the important role of Vitamin D and VDR in brain development and functioning, we hypothesized that several other important behavioural domains may be affected by disruption of the VDR gene in mice. Here we report that VDR mutants display unaffected depressive-like behaviour, but show abnormal social behaviours, reduced social barbering and aggressiveness, impaired nest building and aberrant maternal (pup neglect, cannibalism) behaviours. Taken together, these findings confirm the important role postulated for the VDR in the regulation of behaviour, and suggest the mice lacking functional VDR may be a useful tool to model different brain disorders.

Environmental risk factors for psychosis

Genetic factors are clearly important in the etiology of schizophrenia, but the environment in which an individual's genes find expression is also crucial to the development of the illness. In this review of environmental risk factors for schizophrenia, we consider risks operating prenatally and perinatally, during childhood, and then later in life prior to illness onset. Some of these risk factors have been well documented, for example, early hazards causing fetal growth retardation or hypoxia, and hazards nearer the onset of illness like drug abuse and migration. Others are much less certain. The importance of interaction between genetic and environmental risk is, however, undoubtedly important and there is emerging evidence for this from a range of sources. As the etiology of schiz-ophrenia is unraveled, the picture becomes more complex, but also more obviously relevant to the plight of the individual patient.

Polymorphisms in the vitamin D receptor and their associations with risk of schizophrenia and selected anthropometric measures

The association between vitamin D levels and skeletal growth has long been recognized. However, exposure to low levels of vitamin D during early life is also known to alter brain development, and is a candidate risk factor for schizophrenia. This study examines the association between four polymorphisms in the vitamin D receptor (VDR) and 1) risk of schizophrenia, and 2) three anthropometric variables (height, head size, and head shape). Four single-nucleotide polymorphisms (SNPs; rs10735810/FokI, rs1544410/BsmI, rs7975232/ApaI, and rs731236/TaqI) in the VDR gene were genotyped in 179 individuals with schizophrenia and 189 healthy controls. No significant associations were detected between any of the four VDR SNPs and risk of schizophrenia. Patients were slightly but significantly shorter compared to controls. Of the four SNPs, only rs10735810/FokI was associated with any of the anthropometric measures: the M4 isoform of this SNP was significantly associated with larger head size (P = 0.002). In light of the evidence demonstrating a role for vitamin D during brain development, the association between polymorphisms in VDR and brain development warrants closer scrutiny.