Can vitamin D delay dementia? Study says yes, but critics point out limitations
02 Mar 2023 --- A decade-long study investigating vitamin D and its link to dementia found 40% fewer dementia cases in participants who took dietary supplements, compared to the control group. Supplementation was also positively associated with postponing the development of the disease. However, the study is being criticized by experts as they spot several limitations.
The study included 12,388 participants out of which 2,696 progressed to dementia over ten years. Among them, 75% did not take vitamin D supplements.
In the study, dosing and baseline vitamin D levels were not available and the study did not account for other types of vitamin D exposure, such as sun exposure.
Co-author Dr. Byron Creese from the University of Exeter tells NutritionInsight, “vitamin D is a low risk, low cost and easily deliverable supplement. If it can be conclusively shown to prevent or delay dementia then this would be a major benefit for public health.”
However, professor Tara Spires-Jones, from the UK Dementia Research Institute, notes that it is a large, well-conducted study. However, she adds that it is important to note that this kind of association study cannot prove a causative link between vitamin D and lower dementia risk.
Effect of healthy lifestyles
The authors found 40% fewer dementia diagnoses in a group that took vitamin D supplements.
Dr. Rosa Sancho, head of research at Alzheimer’s Research UK, calls for further evidence.
“To keep our brains healthy as we age, there’s clear evidence that things like not smoking, staying mentally and physically active, only drinking in moderation, and keeping our blood pressure and cholesterol in check all have a positive effect.”
Professor Gill Livingston from University College London notes that dementia takes a long time to develop. “Researchers are always concerned that when follow-up is less than ten years that what we are seeing is a difference between people already developing dementia and those not.”
Creese explains that the study is important for generating hypotheses, but that “a randomized controlled trial where people are randomly assigned to take vitamin D or placebo would help demonstrate a causal effect.”
Vitamin D deficiency
Martin Hewison, professor at the University of Birmingham, adds that “the onset of dementia may prevent people from outdoor activities that normally stimulate their vitamin D production.”
Moreover, as the study relied on self-reporting by participants, Dr. Tom Russ, director of the Alzheimer Scotland Dementia Research Center, reflects that participants may or may not have been taking the supplements consistently.
Preventing dementia is the topic of various studies. The World Health Organization previously stressed that adequate nutrition is essential for brain development.
Study outcomes
The research, conducted by a team from the University of Calgary, Canada, and the University of Exeter, UK, included participants from the US National Alzheimer’s Coordinating Center. The results are published in Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring.
The group’s average age was 71 and all participants were dementia-free when they signed up. During the research, 37% took vitamin D supplements.
The researchers found a significantly more significant effect for vitamin D supplements in women than in men and people with normal cognition compared to those with mild cognitive impairment.
Moreover, the vitamin D effect was more remarkable for people who did not carry the APOEe4 gene, which is the most substantial genetic risk factor for developing Alzheimer’s disease. The authors suggest that carriers of the gene absorb vitamin D more efficiently, which could reduce the effect, although future research is needed.
Follow-up research 
Critics argue that the study cannot prove a causative link between vitamin D and lower dementia risk.
Crees notes that randomized controlled trials might be difficult “as many people already take vitamin D, which is recommended for a range of health benefits.” He adds that there are practical barriers to having someone taking a placebo for 20 years.
“However, at Exeter, we are running a short-term trial of vitamin D for general cognitive function. Genetic methods like Mendelian Randomisation may prove useful as well.”
Hewison adds, “the current study further supports vitamin D supplementation in elderly people. This has musculoskeletal benefits, but it is exciting to think that it may also have some benefits for increasingly common health problems such as Alzheimer’s disease.”
Recent research looked at the effects of vitamin B1 on Alzheimer’s treatment.
By Jolanda van Hal
