Even a moderate deficiency was found to increase the chances of developing the disease by 69%.
Scientists were surprised by the dramatic findings, which suggest that upping vitamin D intake might delay or prevent Alzheimer’s.
But more research has to be done before experts can know if there is a causal link between levels of the vitamin and dementia risk.
The study in the journal Neurology looked at 1,658 American adults aged 65 and over who were free from dementia, heart disease and stroke at the outset.
Lead researcher, Dr David Llewellyn, from the University of Exeter, 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 supplements can delay or even prevent the onset of Alzheimer’s and dementia.
“We need to be cautious at this early stage and our latest results do not demonstrate that low vitamin D levels cause dementia. That said, our findings are very encouraging, and even if a small number of people could benefit, this would have enormous public health implications.”
The research showed that over an average six years, study participants who were moderately deficient in vitamin D had a 53% increased risk of developing any kind of dementia. For those who were severely deficient, the risk increased to 125%.
Similar results were seen for Alzheimer’s, the most common form of dementia. The chances of people lacking vitamin D developing the disease were raised by 69% to 122% depending on how deficient they were. Sunshine is the most important source, but older people’s skin is less efficient at harnessing ultra violet light to manufacture the vitamin.
A. Yes... a re-emergence of cases of rickets in infants and toddlers in recent years, along with emerging evidence, shows there is widespread low levels of the vitamin in the general population.
A. The foods that contain vitamin D, including oily fish, are not commonly consumed by Irish people, so although we rely on our diets to provide us with vitamin D in the winter months, in reality, this can be difficult to achieve.
A. Vitamin D is vital for bone health. Less severe vitamin D deficiency contributes to osteoporosis.