“Vitamin D supplements may INCREASE THE RISK OF DEMENTIA. MORTALITY – AS WELL.”
Some quotes:
“In summary, the results of this study indicate that vitamin D supplements may increase the risk of dementia in older adults and increase the risk of mortality in older adults with Alzheimer’s disease and low blood vitamin D levels. Until our findings prove otherwise, the use of vitamin D supplements for dementia prevention should be reconsidered.”
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“Our population-based longitudinal study also consistently showed that older adults without dementia (n = 14,648) who took vitamin D3 supplements for more than 146 days per year had a 1.8 times HIGHER PROBABILITY OF DEVELOPING DEMENTIA than those who did not take these supplements”, – stated in a Facebook post (language uncorrected).
What study is being discussed?
The numbers quoted on social media are not fabricated. They were taken from a 2022 scientific journal article published in “Aging Cell” by researchers from the Taiwan National Health Research Institutes (NHRI).
It analyzed 14,648 older adults without dementia. The researchers found that in the group of individuals who took vitamin D3 supplements for more than 146 days per year, the probability of a dementia diagnosis was about 1.8 times higher. Separately analyzing data from 980 people already diagnosed with dementia, vitamin D3 use was also associated with a 2.17 times higher risk of mortality.
However, a crucial nuance of the study is omitted in social media posts. The study did not assess the use of regular over-the-counter vitamin D supplements – cholecalciferol – but rather the effect of calcitriol. The start of participant observation in the study was linked specifically to the first date of calcitriol use.
Calcitriol is not the same as the vitamin D3 (cholecalciferol) used in regular dietary supplements. It is the most active vitamin D metabolite, acting as the biologically active form of vitamin D. Due to its strong effect on calcium metabolism, calcitriol can cause hypercalcemia or hypercalciuria, so calcium levels must be monitored and doses adjusted as needed when using it.
That is why calcitriol is not intended for routine vitamin D deficiency supplementation or osteoporosis prevention.
Usually, calcitriol is prescribed only to patients whose kidneys have impaired ability to activate vitamin D – most often in severe kidney failure or hypoparathyroidism. It is also important to note that patients with hypoparathyroidism or kidney diseases have a higher risk of dementia.
This is important when evaluating the study results, as such patients may already have a higher risk of cognitive impairment and dementia due to their health condition and comorbidities.
Moreover, this was an observational, not an interventional study. Therefore, the statistical association found between calcitriol use and increased dementia or mortality risk does not prove that this medication caused these effects.
In other words, the study results cannot be directly applied to regular vitamin D supplement use or used to claim that they cause dementia.
Scientists’ criticism
The study’s conclusions received criticism even within the journal “Aging Cell.” Two scientific commentaries were published questioning the authors’ interpretations.
One of the world’s most renowned vitamin D researchers, clinical biochemist from Canada Reinhold Vieth noted that the publication did not provide clinical evidence that vitamin D supplement use increases the risk of Alzheimer’s disease or dementia, and that inaccurate terminology could mislead readers.
Another group of scientists – researchers from Oregon State University’s Linus Pauling Institute, led by professor and vitamin D biological effects specialist Adrian F. Gombart and colleagues – in their critique stated that the conclusion that vitamin D supplements worsen Alzheimer’s disease progression is not sufficiently supported.
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According to them, the authors combined different types of data in one conclusion – cell culture experiments, mouse studies, and retrospective observations evaluating prescription calcitriol use.
The critics also emphasized that cholecalciferol used in regular supplements and calcitriol are not physiologically or functionally equivalent, so the effect of one cannot automatically be attributed to the other.
Vitamin D protects cognitive functions
The conclusion spread on social media is contradicted by a broader scientific research base. The randomized VITAL trial found that taking 2000 IU of vitamin D3 (cholecalciferol) daily for 2–3 years was not associated with cognitive decline in older adults.
Vitamin D is important not only for physical but also for mental health. Recent studies show that its supplementation may be significant in the context of Alzheimer’s disease and dementia prevention.
Given the enormous burden of dementia – both on healthcare systems and the relatives of those affected – even a partial reduction in the prevalence of this disease could have a very large benefit for society.
A different association was shown by a 2023 prospective study involving 12,388 people. In it, the use of vitamin D preparations – combinations of calcium and vitamin D, cholecalciferol, and ergocalciferol – was associated with about a 40% lower frequency of dementia compared to those who did not use these preparations.
However, this observational study also does not allow the conclusion that vitamin D itself protects against dementia. Still, together with other data, it shows that the categorical claim that regular vitamin D supplements promote dementia development is unfounded.
A meta-analysis published in 2023 showed that low blood vitamin D levels – less than 25 ng/ml – are associated with nearly a 60% higher risk of dementia. Considering that dementia prevalence is already high and continues to grow as the population ages, this increased risk is significant.
However, the study assessed the association between low vitamin D levels and dementia, not whether vitamin D supplementation can reduce this risk. The authors themselves emphasized that additional research is needed to determine whether vitamin D can directly reduce Alzheimer’s disease incidence.
15min verdict: lacking context. The study quotes and numbers circulated on social media are real, but they are presented without essential context. The study evaluated prescription calcitriol use, not regular vitamin D3 supplements, and it was an observational study, so it does not prove that calcitriol caused dementia or cognitive decline.
A broader scientific research base also does not confirm the claim that regular vitamin D supplements increase dementia risk. Therefore, applying this study’s conclusions to all vitamin D supplements and claiming that their use promotes dementia is unfounded.
Publication prepared by 15min in cooperation with Meta, aiming to stop the spread of misleading news on social media. More about the program and its rules – here.
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