Will vitamin D supplements help prevent dementia?

We have been a bit skeptical about many of the claims for various dietary supplements as preventative for Alzheimer's disease and other dementias.  Certainly, if your cognitive issues are caused by a deficiency of vitamin B-12, logic says that taking vitamin B-12 supplements will likely help.  But what about other vitamins?  Evidence has been scant.

About two years ago, I began with a new primary care provider.  He looked at our book and became quite excited.  The story I told and the dementia toolkit were exactly the things he'd been telling his patients.  But he did say he thought I should add vitamin D supplements to my diet.  I followed his plan and then had my vitamin D measured.  The value measured was through the roof, so I significantly backed off.  Nonetheless, I have continued to take 50 mcg of vitamin D3 twice a day since.

Vitamin D is technically not a vitamin, but rather a hormone.  It is manufactured in the bodies of mammals when their skin is exposed to sunlight, and it works to signal the regulation of certain biological processes.  That is what hormones do - signal processes.

So does taking vitamin D supplements affect someone's susceptibility to Alzheimer's disease and dementia?  There is some evidence that it does.  An article published in the March 2023 journal Alzheimer's and Dementia; Diagnosis, assessment, and disease monitoring provides the results of a study of a large population of subjects (12,388) with regard to use of vitamin D supplements and incidence of dementia.  Data on the subjects were found in existing databases from several sources.  The results?  "Across all formulations, vitamin D exposure was associated with significantly longer dementia-free survival and lower dementia incidence rate than no exposure."  In other words, people who took vitamin D supplements had a lower incidence of dementia.

But, as usual, the devil is in the details.  This was a longitudinal study.  Longitudinal studies infer cause and effect relationships by studying behaviors of populations.  They are not "interventional" or "experimental" studies.  The latter will make a change and measure results, often comparing results to a placebo.  Cause and effect relationships can be much more reliably established with experimental studies than with longitudinal studies. Also, variation was found in sex differences, which variant of the APOE gene one carries, and other variables.

Nevertheless, the results were intriguing.  

How might this work?  Vitamin D is involved in many biologic processes.  One suggestion is that it is involved with the clearance of beta amyloid in the brain.  Sort of like those monoclonal antibodies that have been in the news.

I will continue to take vitamin D supplements -- as recommended by my primary care provider.

You can read more about this study here.