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Dementia is associated with low vitamin D - several studies

Alzheimers-Cognition - Overview

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Vitamin D deficiency as a risk factor for dementia: a systematic review and meta-analysis - 2017

BMC Geriatrics volume 17, Article number: 16 (2017)
Isolde Sommer, Ursula Griebler, Christina Kien, Stefanie Auer, Irma Klerings, Renate Hammer, Peter Holzer & Gerald Gartlehner
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Background
Sunlight exposure and high vitamin D status have been hypothesised to reduce the risk of developing dementia. The objective of our research was to determine whether lack of sunlight and hypovitaminosis D over time are associated with dementia.

Methods
We systematically searched MEDLINE (via PubMed), Cochrane Library, EMBASE, SCOPUS, Web of Science, ICONDA, and reference lists of pertinent review articles from 1990 to October 2015. We conducted random effects meta-analyses of published and unpublished data to evaluate the influence of sunlight exposure or vitamin D as a surrogate marker on dementia risk.

Results
We could not identify a single study investigating the association between sunlight exposure and dementia risk. Six cohort studies provided data on the effect of serum vitamin D concentration on dementia risk. A meta-analysis of five studies showed a higher risk for persons with serious vitamin D deficiency (<25 nmol/L or 7–28 nmol/L) compared to persons with sufficient vitamin D supply (≥50 nmol/L or 54–159 nmol/L) (point estimate 1.54; 95% CI 1.19–1.99, I2 = 20%). The strength of evidence that serious vitamin D deficiency increases the risk of developing dementia, however, is very low due to the observational nature of included studies and their lack of adjustment for residual or important confounders (e.g. ApoE ε4 genotype), as well as the indirect relationship between Vitamin D concentrations as a surrogate for sunlight exposure and dementia risk.

Conclusions
The results of this systematic review show that low vitamin D levels might contribute to the development of dementia. Further research examining the direct and indirect relationship between sunlight exposure and dementia risk is needed. Such research should involve large-scale cohort studies with homogeneous and repeated assessment of vitamin D concentrations or sunlight exposure and dementia outcomes.


Quality assessment of systematic reviews of vitamin D, cognition and dementia - 2018

BJPsych Open. 2018 Jul;4(4):238-249. doi: 10.1192/bjo.2018.32.
Aghajafari F1, Pond D2, Catzikiris N3, Cameron I4.

  • 1 Assistant Professor, Dept of Family Medicine, Cumming School of Medicine, U. of Calgary Sunridge Family Medicine Teaching Centre, Canada.
  • 2 Professor and Head of Department of Family Medicine, University of Newcastle, Australia.
  • 3 Research Assistant, School of Medicine and Public Health, Faculty of Medicine, The University of Newcastle, Australia.
  • 4 Professor, Northern Clinical School, Rehabilitation Studies Unit, Sydney Medical School, The University of Sydney, Australia.

BACKGROUND: There is conflicting evidence regarding the association of vitamin D with cognition performance and dementia.

Aims We aimed to summarise the evidence on the association of vitamin D with cognitive performance, dementia and Alzheimer disease through a qualitative assessment of available systematic reviews and meta-analyses.

METHOD: We conducted an overview of the systematic reviews of all study types with or without meta-analyses on vitamin D and either Alzheimer disease, dementia or cognitive performance up to June 2017.

RESULTS:
Eleven systematic reviews were identified, nine of which were meta-analyses with substantial heterogeneity, differing statistical methods, variable methodological quality and quality of data abstraction. A Measurement Tool to Assess Systematic Reviews checklist scores ranged from 4 to 10 out of 11, with seven reviews of 'moderate' and four of 'high' methodological quality.
Out of six meta-analyses on the association between low serum concentration of 25-hydroxyvitamin D and risk of dementia, five showed a positive association. Results of meta-analyses on the association between low serum concentration of 25-hydroxyvitamin D and memory function tests showed conflicting results.

CONCLUSIONS:
This systematic evaluation of available systematic reviews provided a clearer understanding of the potential link between low serum vitamin D concentrations and dementia. This evaluation also showed that the quality of the available evidence is not optimal because of both the low methodological quality of the reviews and low quality of the original studies. Interpretation of these systematic reviews should therefore be made with care.

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