How is vitamin D deficiency related to the risk of Alzheimer’s disease?

Genetically decreased vitamin D and risk of Alzheimer disease.

Mokry LE, Ross S, Morris JA, Manousaki D, Forgetta V, Richards JB.

Neurology 2016; 87:2567-2574.

Abstract

OBJECTIVE:

To test whether genetically decreased vitamin D levels are associated with Alzheimer disease (AD) using mendelian randomization (MR), a method that minimizes bias due to confounding or reverse causation.

METHODS:

We selected single nucleotide polymorphisms (SNPs) that are strongly associated with 25-hydroxyvitamin D (25OHD) levels (p < 5 × 10-8) from the Study of Underlying Genetic Determinants of Vitamin D and Highly Related Traits (SUNLIGHT) Consortium (N = 33,996) to act as instrumental variables for the MR study. We measured the effect of each of these SNPs on 25OHD levels in the Canadian Multicentre Osteoporosis Study (CaMos; N = 2,347) and obtained the corresponding effect estimates for each SNP on AD risk from the International Genomics of Alzheimer’s Project (N = 17,008 AD cases and 37,154 controls). To produce MR estimates, we weighted the effect of each SNP on AD by its effect on 25OHD and meta-analyzed these estimates using a fixed-effects model to provide a summary effect estimate.

RESULTS:

The SUNLIGHT Consortium identified 4 SNPs to be genome-wide significant for 25OHD, which described 2.44% of the variance in 25OHD in CaMos. All 4 SNPs map to genes within the vitamin D metabolic pathway. MR analyses demonstrated that a 1-SD decrease in natural log-transformed 25OHD increased AD risk by 25% (odds ratio 1.25, 95% confidence interval 1.03-1.51, p = 0.021). After sensitivity analysis in which we removed SNPs possibly influenced by pleiotropy and population stratification, the results were largely unchanged.

CONCLUSIONS:

Our results provide evidence supporting 25OHD as a causal risk factor for AD. These findings provide further rationale to understand the effect of vitamin D supplementation on cognition and AD risk in randomized controlled trials.

This reference is now included in the neurochecklist:

Alzheimer’s disease (AD): risk factors

screen-shot-2016-12-24-at-23-32-53

Abstract link

Alzheimer's disease, spread through the brain. NIH Image Gallery on Flikr. https://www.flickr.com/photos/nihgov/24524716351
Alzheimer’s disease, spread through the brain. NIH Image Gallery on Flikr. https://www.flickr.com/photos/nihgov/24524716351

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