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Vitamin D supplements may reduce the risk of dementia

Last updated on August 17th, 2023 at 11:40 am

Vitamin D has become one of those supplements that seem to be on everyone’s mind these days. I’ve heard all kinds of claims about the supplement, especially since the COVID-19 pandemic when there was a lot of conflicting information as to whether vitamin D could improve outcomes from the disease. Let’s just say the evidence is mixed.

I have read a lot of research about vitamin D, and I ran into a new, large observational study published in a peer-reviewed journal that shows that vitamin D supplements can reduce the risk of dementia. However, and there is always a however, the study had some crucial limitations that need to be discussed to appreciate whether there is a causal link.

I have written a few articles about dementia and Alzheimer’s disease recently because I am interested in understanding correlation versus causation. We need to determine if there is actually a causal link between vitamin D and the risk of dementia.

As I usually do, I want to provide some of the results of the study and some critiques that might be important to understanding if we are actually observing a causal relationship between vitamin D and dementia.

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What is dementia?

Dementia is a condition where there is a loss of mental functions that have an effect on daily life. Symptoms of dementia can be the loss of:

  • Memory
  • Language skills
  • Visual perception (your ability to make sense of what you see)
  • Problem-solving
  • Difficulty with everyday tasks
  • The ability to focus and pay attention

Dementia is often conflated with Alzheimer’s disease, but Alzheimer’s is just one of many forms of dementia. These include:

  • Alzheimer’s disease, which is characterized by protein plaques and “tangles” around the neurons of the brain which eventually cause the loss of mental function.
  • Lewy body dementia, which causes movement symptoms along with dementia. Lewy bodies are abnormal deposits of a protein in the brain.
  • Frontotemporal disorders, which cause changes to certain parts of the brain.
  • Vascular dementia, which involves changes to the brain’s blood supply. It is often caused by a stroke or atherosclerosis (hardening of the arteries) in the brain.
  • Mixed dementia, which is a combination of two or more types of dementia.

We do not know what causes most forms of dementia. Unfortunately, we cannot prevent or “cure” any of the forms of dementia, although there may be some methods that can temporarily reduce the severity or onset of the disease. Right now, a lot of research is concentrated on these conditions, such as Alzheimer’s disease, but we have not uncovered the basic cause which prevents research from finding the actual cure.

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Vitamin D and dementia paper

In a paper published 01 March 2023 in Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring, Zahinorr Ismail, MD, Department of Psychiatry, Cumming School of Medicine, University of Calgary, and colleagues studied 12,388 participants in the National Institute on Aging National Alzheimer’s Coordinating Center (NACC) database who had normal cognition or mild cognitive impairment at baseline. These participants came from Alzheimer’s Disease Research Centers from 2005 to 2021.

Exposure to vitamin D supplementation was based on NACC medication forms that assessed three formulations: calcium-vitamin D, cholecalciferol, and ergocalciferol. Participants with baseline exposure to any vitamin D supplement were considered the vitamin D-exposed group, while those without any exposure at all study visits were considered non-exposed. People with no baseline exposure who subsequently were exposed to vitamin D were excluded.

They found that associated individuals with exposure to vitamin D supplementation exhibited a 40% lower dementia incidence rate compared with no exposure. Effects were greater in females, in apolipoprotein E ε4 (APOE4), a protein that may be involved in Alzheimer’s disease, non-carriers, and in people with normal cognition versus those with mild cognitive impairment.

Five-year dementia-free survival was 83.6% for those exposed to vitamin D and 68.4% for the non-exposed group, a statistically significant difference.

Furthermore, both mild cognitive impairment and depression were more frequent in the non-exposed group.

Critique of vitamin D and dementia

As with most studies with supplements, there are numerous limitations to this type of study. They are, in no particular order of importance:

  1. There was no information about exposure to vitamin D history. We don’t know if people who took vitamin D supplements were doing it for years or decades before the study.
  2. There was no dose-response curve. What was the proper level of vitamin D that had the highest reduction in dementia risk?
  3. The researchers could not determine which participants may have been suffering from deficient vitamin D levels before or during supplementation.
  4. There could be confounding factors, such as whether those who took vitamin D supplements also had a healthier diet, were more active, or something else. This is an issue with many nutritional studies that really should be included to improve the quality of the studies.

So does this mean that I or you should run down to our local pharmacy and pick up a big bottle of vitamin D to prevent dementia in the future? I am not convinced, though there is enough weak, but persistent, evidence that individuals with low levels of vitamin D are at higher risks of many conditions.

But that’s the key point I want to make. Have your vitamin D levels checked, then determine whether you should consume a supplement. Also, just because you have a good blood level of vitamin D does not mean you should swallow a handful of the vitamin because you think that “if a little works a lot will work even more.”

That’s not how vitamins work. Your body will rid itself of excess vitamin D because it’s actually dangerous to have excess levels. Vitamin D toxicity can be harmful, so don’t think that taking a handful of capsules every day is going to prevent dementia down the road.

Right now, I am intrigued by this study, but I am far from convinced that there is a causal link between vitamin D levels and dementia risk. I would need to have some better cohort or case-control studies before I become convinced.

Personally, I have my blood levels of vitamin D checked annually. And I take a vitamin D supplement (prescribed by my physician) to maintain a proper level of it. And I eat a lot of fish, so that also helps keep a higher level of the vitamin. I’ll get back to you in 30 or 40 years to discuss my mental fitness.


Michael Simpson

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