Low levels of vitamin D in elderly men and women can double the risk of developing dementia in later life according to one of the biggest studies of its kind into the nutritional supplement.
Senile dementia and Alzheimer’s disease were both significantly higher in people with low levels of vitamin D, compared to those with normal levels, when tested up to six years before the onset of symptoms, scientists found.
The findings suggest that taking vitamin D – which is also made by the skin when exposed to sunlight – could protect people against the onset of dementia, especially at northern latitudes where there are low levels of sunlight during winter months.
Some scientists have argued that vitamin D is actually a hormone rather than a vitamin and a deficiency should be treated more seriously than it is because of the increasing realisation that it is linked with a wide range of illnesses.
The latest study, published in the journal Neurology, monitored vitamin D levels in the blood of 1,659 people aged 65 and over who were free of dementia, cardiovascular disease and stroke at the time they were first tested.
Over the following six years, the scientists found that those who were moderately deficient in vitamin D were at 53 per cent higher risk of dementia, and a 69 per cent higher risk of Alzheimer’s disease, than those with normal levels of the vitamin.
In even more severely deficient people, the risk of dementia jumped to 125 per cent while there was a 122 per cent increased risk of developing Alzheimer’s disease – a dose-response finding showing that levels of vitamin D were a significant risk factor in both kinds of progressive brain illnesses.
“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 the association was twice as strong as we anticipated,” said David Llewellyn of the University of Exeter.
Previous research has established a link between low levels of vitamin D and the onset of cognitive problems but this study found confirmed a significant association with both dementia and Alzheimer’s disease.
“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,” Dr Llewellyn said.
“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,” he said.
“Even if a small number of people could benefit, this would have enormous public health implications given the devastating and costly nature of dementia,” he added.
The number of people with dementia is expected to triple over the next half century as the population ages so even if a small number of people can benefit from taking vitamin D supplements, it will have a major impact on the costs of treating the illness, said Professor Gordon Wilcock of the University of Oxford.
“One could make a case for checking vitamin D levels in older people who have a poor diet, or who have little exposure to the sun, or alternatively as a part of an older persons’ routine screening programme, because vitamin D is important for other health reasons as well as memory problems and dementia,” Professor Wilcock said.
“Dementia is such a devastating disease that preventing or slowing down its progression, if this proves possible with vitamin D supplements, would be extremely important even if the number of people who benefited seems small,” he said.
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