Study Shows Causal Relationship Between Vitamin D Deficiency and Dementia

A pathologist holding up a vitamin D test. Jarun Ontakrai/Shutterstock

An Australian study has found that deficiency in vitamin D has a causal relationship with the development of dementia, with both inadequacy and excessive levels of the vitamin associated with a smaller brain volume.

“Our findings have important implications for dementia risks,” said professor Elina Hyppönen from the University of South Australia. “In this UK population, we observed that up to 17 percent of dementia cases might have been avoided by boosting vitamin D levels to be within a normal range.”

The study, published in the American Journal of Clinical Nutrition, measured individuals’ vitamin D3 levels as an overall estimate of vitamin D levels.

The findings indicated that individuals who were inadequate in vitamin D—having a level below 12 ng/ml—had a 54 percent greater risk of dementia compared to individuals with levels at around 20 ng/ml—the recommended level by the Institute of Medicine.

Further, individuals with higher vitamin D3 levels above 20 ng/ml, especially in the extremes, were also at a greater risk of dementia. Though people that were deficient still had the highest risks.

The researchers observed that people who were inadequate and those in excess were all associated with MRI scans showing lower total brain volume, as well as lower brain volume in gray and white matter.

Reduced volumes in these three measures are all markers linked with brain shrinkage and an elevated risk of “cognitive decline and dementia.”

Further, as individuals’ vitamin D3 levels increased from inadequacy to the recommended standard, researchers also observed a reduced trend for dementia risks.

MRI scans of different individuals with vitamin levels within this increase showed gradual increases in total brain, grey matter, and white matter volumes. However, this risk-reducing trend stops when the concentration exceeds 20 ng/ml.

As part of the study, the researchers evaluated almost 300,000 individuals within the UK database on their vitamin D3 levels and brain MRI scans. Participants of the ongoing study were recruited from 2006 to 2010 and were aged 37 to 72 at the time of recruitment, with data collection still ongoing.

Dementia is a general state commonly associated with memory loss and impaired judgment. The condition is often linked with brain atrophy—the shrinking of the brain due to losses of neurons and connections.

The researchers observed a non-linear U-shaped causal relationship between dementia and vitamin D3, indicating that the strongest associations for dementia and vitamin D3 lie at the two extremes in their concentration levels.

The authors noted the relationship as a threshold effect, meaning that the relationship between dementia and vitamin D3 can only be seen at certain concentrations.

Previous studies also indicated the presence of thresholds in the form of non-linear relationships, suggesting a balance in the intake of various nutrients.

Vitamin D is an important molecule within our body’s metabolism, and serves as a “hormone precursor” that has become increasingly recognized for widespread health effects, including brain health, said Hyppönen.

Within the brain as well, vitamin D regulates neuronal pathways. Findings from laboratory studies suggest that the vitamin protects neurons by balancing calcium in the immune system to reduce nerve inflammation. Low vitamin D has also been associated with cognitive and memory decline.

The researchers said their study highlighted the important link between vitamin D and dementia, reinforcing previous studies that related vitamin D to brain health.

The authors suggest larger studies “to confirm causality for the proposed associations” between vitamin D concentrations and brain morphology, indicating that the causal relationship between vitamins and dementia risks “provides an important opportunity for prevention.”