Older people are more than twice as likely to develop dementia and Alzheimer’s disease if they are severely Vitamin D deficient, according to the most robust study of its kind ever conducted.
An international team, led by Dr David Llewellyn at the University of Exeter Medical School, funded in part by the Alzheimer's Association and supported by NIHR CLAHRC South West Peninsula (also known as PenCLAHRC), studied elderly Americans who took part in the Cardiovascular Health Study. They discovered that adults who were moderately deficient in vitamin D had a 53 per cent increased risk of developing dementia of any kind, and the risk increased to 125 per cent in those who were severely deficient.
Similar results were recorded for Alzheimer’s disease, with the moderately deficient group 69 per cent more likely to develop this type of dementia, jumping to a 122 per cent increased risk for those severely deficient.
The study looked at 1,658 adults aged 65 and over, who were able to walk unaided and were free from dementia, cardiovascular disease and stroke at the start of the study. The participants were then followed for six years to investigate who went on to develop Alzheimer’s disease and other forms of dementia.
Dr Llewellyn said: “We expected to find an association between low Vitamin D levels and the risk of dementia and Alzheimer’s disease, but the results were surprising – we actually found that the association was twice as strong as we anticipated.
“Clinical trials are now needed to establish whether eating foods such as oily fish or taking vitamin D supplements can delay or even prevent the onset of Alzheimer’s disease and dementia. We need to be cautious at this early stage. That said, our findings are very encouraging, and even if a small number of people benefit, this could have enormous public health implications given the devastating and costly nature of dementia.”
The research is the first large study to investigate the relationship between vitamin D and dementia risk where the diagnosis was made by an expert multidisciplinary team, using a wide range of information including neuroimaging. Previous research established that people with low vitamin D levels are more likely to go on to experience cognitive problems, but this study confirms that this translates into a substantial increase in the risk of Alzheimer’s disease and dementia.
The study also found evidence that there is a threshold level of Vitamin D circulating in the bloodstream below which the risk of developing dementia and Alzheimer’s disease increases. The team had previously hypothesized that this might lie in the region of 25-50 nmol/L, and their new findings confirm that vitamin D levels above 50 nmol/L are most strongly associated with good brain health.
Vitamin D comes from three main sources – exposure of skin to sunlight, foods such as oily fish, and supplements. Older people’s skin can be less efficient at converting sunlight into Vitamin D, making them more likely to be deficient and reliant on other sources. In many countries the amount of UVB radiation in winter is too low to allow vitamin D production.
Collaborators on this research included Angers University Hospital, Florida International University, Columbia University, the University of Washington, the University of Pittsburg and the University of Michigan. The study also received funding from the Mary Kinross Charitable Trust, the James Tudor Foundation, the Halpin Trust, the Age Related Diseases and Health Trust and the Norman Family Charitable Trust.
BBC news and radio coverage of this story is available here.