Older people with low levels of vitamin D appear more likely to have problems with memory, learning, and thinking, suggesting low vitamin D could give an early warning for dementia risk, say scientists.
Researchers from Britain, Italy, and the United States studied 850 Italians aged 65 or older and found that those who were severely vitamin D deficient were 60 percent more likely to experience substantial general cognitive decline, and 31 percent more likely to experience problems with mental flexibility.
"This is the first study to identify a clear link between low vitamin D levels and cognitive decline," said David Llewellyn of the Peninsula Medical School at Britain's Exeter University, who led the study.
"We have now been able to demonstrate a connection between having low levels of vitamin D and going on to develop cognitive problems."
Since an estimated 1 billion people worldwide have insufficient levels of vitamin D, Llewellyn said the findings were "a cause for real concern."
Giving vitamin D supplements to older people to boost their levels could be "a highly promising therapeutic target for the prevention of dementia," he said, particularly since supplements are cheap, safe, and have already been shown to help reduce the risk of falls and fractures.
Most vitamin D is made by the body as a natural by-product of the skin's exposure to sunlight. It can also be found in a few foods, such as oily fish, and is vital for health, as it helps cells absorb calcium and is key for bone strength.
Some recent studies have also suggested vitamin D may protect against cancer, artery disease, and tuberculosis.
In this study, Llewellyn's team found that older people who were severely deficient in vitamin D — defined as having blood levels of 25-hydroxyvitamin D of less than 25 nanomoles per liter — were 60 percent more likely to have substantial cognitive decline over a six-year period studied.
They were also 31 percent more likely to show decline in a test measuring executive function than those with good vitamin D levels. The findings were published in the Archives of Internal Medicine journal.
Dementia is a brain-wasting condition that affects around 35 million people worldwide.
Its most common form is Alzheimer's disease, in which patients gradually lose their memory, their ability to navigate and understand the world around them, and to look after themselves. Despite decades of research, doctors still have few effective weapons against it.
Llewellyn's team said they thought Vitamin D may help prevent the degeneration of brain tissue by having a role in forming nervous tissue, maintaining levels of calcium in the body, or clearing of beta-amyloid, the substance that forms the brain plaques that are associated with Alzheimer's disease.
Experts estimated that in the United States and Europe, between 40 to 100 percent of older adults are deficient in vitamin D, and the problem is aggravated in the elderly as they spend more time indoors and their skin becomes less efficient at producing vitamin D with age.
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