Vitamin D Unlikely to Protect Against Neurodegenerative Diseases, Systematic Review Finds
Summary: Researchers report they have found little convincing evidence to support the claim that vitamin D acts as a neuroprotective agent.
Source: University of Adelaide
New research from South Australian scientists indicates that vitamin D — commonly called the “sunshine vitamin” — is unlikely to offer protection against multiple sclerosis, Parkinson’s disease, Alzheimer’s disease or other neurodegenerative conditions.
The findings, published in the journal Nutritional Neuroscience, come from a systematic review that examined both preclinical and clinical studies and concluded there is insufficient evidence to support vitamin D as a protective neurological agent.
“Our work challenges a growing belief that higher vitamin D levels can directly improve brain health,” says Krystal Iacopetta, PhD candidate at the University of Adelaide and lead author of the review.
Ms Iacopetta and colleagues conducted a systematic assessment of more than 70 relevant studies, evaluating the quality of evidence for vitamin D across a range of neurodegenerative diseases. Their review included observational studies, animal and cellular experiments, and clinical trials where available.
Earlier observational research has shown that people with neurodegenerative disease often have lower measured vitamin D levels than healthy controls. That correlation led to the hypothesis that raising vitamin D levels — through increased safe sun exposure or supplements — could reduce disease risk or slow progression.
However, after evaluating study design, sample sizes, treatment effects, and the balance between intervention and control groups, the review team found that most supportive evidence for neuroprotection comes from observational and preclinical studies rather than robust clinical trials.
“The association between low vitamin D and brain disorders appears to be just that — an association — rather than proof of a causal, protective effect,” Ms Iacopetta explains. “We could not identify convincing clinical evidence that vitamin D provides neuroprotective benefit for any condition we investigated.”
Professor Mark Hutchinson, Director of the ARC Centre of Excellence for Nanoscale Biophotonics (CNBP) and co-author of the review, emphasizes the importance of the comprehensive approach the team used.
“This outcome is significant because it is based on a thorough review and objective analysis of the available data,” Professor Hutchinson says. “We have challenged the common assumption that vitamin D produced by sun exposure is directly good for the brain.”
Importantly, Professor Hutchinson notes that the evidence does not rule out a beneficial effect of sun exposure on brain health; it merely indicates that the protective mechanism may not be vitamin D synthesis. Early studies hint that ultraviolet (UV) light could influence molecular processes in the brain through pathways independent of vitamin D production.
“There are indications that UV exposure could positively impact some neurological conditions, such as multiple sclerosis, by mechanisms unrelated to vitamin D,” he says. “More targeted research is needed to identify these mechanisms and understand how sun exposure interacts with brain biology.”
“While sensible, safe sun exposure might have positive effects on brain health, vitamin D itself — although essential for general health — does not appear to be the miracle ‘sunshine tablet’ solution for neurodegenerative diseases that some have hoped for,” Professor Hutchinson says.
The systematic review was conducted by researchers affiliated with the University of Adelaide, the University of South Australia and the ARC Centre of Excellence for Nanoscale Biophotonics (CNBP). The review aimed to compare the neuroprotective potential of vitamin D derived endogenously from UV exposure with vitamin D obtained through supplements.
Original Research: Abstract for “Are the protective benefits of vitamin D in neurodegenerative disease dependent on route of administration? A systematic review” by Krystal Iacopetta et al., published July 9, 2018, in Nutritional Neuroscience. The authors analysed 231 screened articles and included 73 studies that met strict inclusion criteria.
Abstract (Summary)
Background: Interest in vitamin D’s therapeutic properties has grown over the past decade due to associative evidence suggesting neuroprotective effects. It remains unclear whether low vitamin D contributes to the onset of neurological disorders or reflects disease-related changes.
Objectives: The review quantitatively assessed whether any neuroprotective benefits of vitamin D depend on the route of administration — comparing UV-derived endogenous vitamin D with exogenous supplementation.
Design: The authors systematically searched PubMed, Embase and PsycInfo for both preclinical and clinical studies. Eligible articles were assessed for methodological quality and data were analysed to identify publication trends and study characteristics.
Results: Of 231 articles screened, 73 met inclusion criteria. Findings indicate insufficient evidence to conclude a neuroprotective role for vitamin D or to determine whether route of administration is relevant. Most supportive data come from preclinical and observational studies; rigorous clinical evidence is lacking. Sun exposure may protect against multiple sclerosis, Parkinson’s disease and Alzheimer’s disease through mechanisms independent of vitamin D, but further research is needed. Evidence for amyotrophic lateral sclerosis was limited and inconclusive.
Conclusion: Strong therapeutic recommendations for vitamin D in neurodegenerative disease cannot be made based on current evidence. It remains uncertain whether vitamin D mediates protection or simply marks sun exposure, which may involve other, as yet unidentified neuroprotective factors.
MLA: University of Adelaide. “Vitamin D No Defense Against Dementia or MS.” NeuroscienceNews, 10 July 2018.
APA: University of Adelaide (2018, July 10). Vitamin D No Defense Against Dementia or MS. NeuroscienceNews.
Chicago: University of Adelaide. “Vitamin D No Defense Against Dementia or MS.” (Accessed July 10, 2018).