A recent meta-analysis published in the Nutrition Journal discovered that lower vitamin D status may be associated with an increased risk of developing Alzheimer’s disease and dementia.
An estimated 47.5 million people suffer from dementia worldwide, with Alzheimer’s disease accounting for about 60-70% of the cases. Despite large research efforts devoted to finding treatments, a cure for dementia has yet to be discovered. Therefore, prevention strategies are in urgent need.
Studies have found a high prevalence of vitamin D deficiency among patients with AD or dementia. Researchers recently conducted a meta-analysis in order to gain more insight on the relationship between vitamin D status and dementia.
Meta-analyses play an important role in research if conducted well. Many studies will show contrary findings, and it becomes challenging to understand whether a certain exposure (i.e. vitamin D) is associated with an outcome (i.e. dementia). Meta-analyses pool data from individual studies as if they were part of one very large experiment. The inclusion of multiple studies minimizes biases that could potentially skew the results, while producing a conclusion with more statistical power.
Arguably the most important factor of a meta-analysis is its inclusion criteria. A meta-analysis’s results can still be misleading if it does not exclude poor quality studies. Additionally, the meta-analyses should only include studies with similar designs.
The current meta-analysis had found 298 studies on vitamin D and dementia or vitamin D and AD. The researchers included studies if it fit the following criteria: an original study that evaluated the association between vitamin D status and risk of developing AD or dementia, provided specific statistical measurements, compared vitamin D deficient individuals to subjects with vitamin D levels greater than 20 ng/ml (50 nmol/L). The researchers excluded animal experiments, reviews and mechanistic research studies.
A total of five studies fit the inclusion criteria. Two studies were prospective cohorts and three were cross-sectional. All studies were published after 2010.
The researchers found that subjects with vitamin D deficiency as defined by levels less than 20 ng/ml (50 nmol/L) were at an increased risk of developing AD by 21% in comparison to those with vitamin D levels above 20 ng/ml (50 nmol/L). Additionally, those who were considered vitamin D deficient had a 63% increased risk of developing dementia in comparison to those who were vitamin D sufficient.
The researchers stated,
“In summary, available data shows that vitamin D deficiency may be associated with increased risk of developing AD and dementia.”
They stated the implications of the findings,
“In addition, in view of the safe and cost-effective interventions to improve vitamin D status, the potential beneficial effects of vitamin D supplementation in preventing AD and dementia should be paid attention to and assessed by the neurologists and geriatricians.”
As with any study, it’s important to critically assess its findings. First, as the researchers noted, the number of eligible studies to include was relatively small. The researchers did not use a technique to assess the quality of the studies included, meaning that studies of poor quality may have been included. Lastly, the available data did not allow the researchers to prove causation. Thus, we do not know whether vitamin D deficiency caused AD or dementia, only that a relationship exists.
Further research is needed to further confirm this relationship and to assess the effects of vitamin D supplementation in the prevention of AD and dementia.
Citation of article
Tovey, A. Meta-analysis suggests vitamin D deficiency may increase the risk of developing Alzheimer’s disease and dementia. The Vitamin D Council Newsletter, 2015.