Adults in a recent study 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.
Vitamin D deficiency is
associated with a substantially increased risk of dementia and Alzheimer's
disease in older people, 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, found that study participants who were severely Vitamin D deficient were more than twice as likely to develop dementia and Alzheimer's disease.
The team studied elderly
Americans who took part in the Cardiovascular Health Study. They discovered
that adults in the study 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 was part-funded by
the Alzheimer's Association, and is published in Neurology, the
medical journal of the American Academy of Neurology. It 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 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 given the
devastating and costly nature of dementia."
Research collaborators included
experts from Angers University Hospital, Florida International University,
Columbia University, the University of Washington, the University of Pittsburg
and the University of Michigan. The study was supported by the Alzheimer's
Association, the Mary Kinross Charitable Trust, the James Tudor Foundation, the
Halpin Trust, the Age Related Diseases and Health Trust, the Norman Family
Charitable Trust, and the National Institute for Health Research Collaboration
for Leadership in Applied Research and Care South West Peninsula (NIHR
PenCLAHRC).
Dementia is one of the greatest
challenges of our time, with 44 million cases worldwide -- a number expected to
triple by 2050 as a result of rapid population aging. A billion people
worldwide are thought to have low vitamin D levels and many older adults may
experience poorer health as a result.
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.
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.
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.
Commenting on the study, Dr Doug
Brown, Director of Research and Development at Alzheimer's Society said:
"Shedding light on risk factors for dementia is one of the most important
tasks facing today's health researchers. While earlier studies have suggested
that a lack of the sunshine vitamin is linked to an increased risk of
Alzheimer's disease, this study found that people with very low vitamin D
levels were more than twice as likely to develop any kind of dementia.
"During this hottest of
summers, hitting the beach for just 15 minutes of sunshine is enough to boost
your vitamin D levels. However, we're not quite ready to say that sunlight or
vitamin D supplements will reduce your risk of dementia. Large scale clinical
trials are needed to determine whether increasing vitamin D levels in those
with deficiencies can help prevent the dementia from developing."
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