Study linking vitamin D with lower dementia rate ‘limited in its conclusions’

Researchers exploring the link between vitamin D supplementation and incident dementia found that, across all groups, exposure to the nutrient was associated with significantly longer dementia-free survival and a 40% lower dementia incidence rate.

The study, which was published in Alzheimer's and Dementia: Diagnosis, Assessment and Disease Monitoring, involved 12,388 participants from the US-based National Alzheimer's Co-ordinating Center dataset.

‘Normal’ levels of vitamin D may prevent dementia

The findings support previous research suggesting that vitamin D supplementation may be a potential agent for dementia prevention, particularly in high-risk groups. However, despite the link, the role of supplementation remains unclear. 

The nutrient is known to have cognitive health effects and has been associated with a significantly lower rate of autoimmune conditions.

A 2022 study concluded that, in some populations, having “normal” levels of vitamin D – that is, 50 nanomoles per litre (nmol/L) – could prevent dementia cases in as many as 17% of people. 

Vitamin D effects greater in females and Apo-ε4 non-carriers

In this study, which was led by researchers from the University of Calgary in Canada and Exeter University in the UK, incidence varied according to gender, cognitive status, and apolipoprotein ε4 (Apo-ε4) status.

Vitamin D effects were significantly greater in females and Apo-ε4 non-carriers. Apo-ε4, a subtype of a protein involved in the metabolism of fats in the body of mammals, has been implicated in Alzheimer's disease.

The authors conclude: “Future clinical trials should consider dosing of vitamin D supplementation, while paying close attention to baseline serum vitamin D levels. Clarifying exposure duration, dose–response relationships, and the role of vitamin D deficiency will be necessary to inform intervention studies.”

Research fails to account for all potential confounding factors

Dr Tom Russ, director of the Alzheimer Scotland Dementia Research Centre, called the research “interesting” but pointed to limitations with the methodology.

Dr Russ, who is also consultant psychiatrist and honorary clinical reader at the University of Edinburgh, said: “Like all observational studies, this research is limited in its conclusions. It used a large, high-quality database to conduct the research, but the vitamin D supplementation was based on self-report and participants may or may not have been taking these consistently.

“It was also not possible for them to know which participants were vitamin D-deficient and which had enough, which is likely the most important thing. They included some important risk factors which could potentially confound the association, but not all known risk factors for dementia which could be relevant.

“Previous evidence – particularly from Mendelian randomisation studies – strongly implicates low levels of vitamin D as a risk factor for dementia, but we really need high-quality studies which identify vitamin D-deficient individuals and replace this to see if this affects their risk of dementia.”