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Alzheimer's Disease

Vitamin D Deficiency Linked to Dementia

Researchers say vitamin may protect brain against Alzheimer’s disease

Older men and women with low levels of vitamin D are nearly four times as likely to have problems with their memory, attention and logic, according to a new study presented this week at the Alzheimer’s Association’s International Conference in Honolulu. The study suggests a link between vitamin D deficiency and an increased risk of cognitive decline and dementia later in life.

Interest in the “sunshine” vitamin has intensified recently as more and more research suggests it may play a role in a variety of diseases associated with aging, including heart disease, some cancers and diabetes.

Researchers led by David Llewellyn, a neuropsychologist at the University of Exeter in England, analyzed information about 3,325 adults age 65 and older in a study that was carefully designed to reflect America’s older population. Their report documents a relationship between low vitamin D levels and impaired thinking. They found that the likelihood of performing poorly on tests of memory and attention was about 42 percent higher in people who were vitamin D deficient and nearly 400 percent higher in people who were severely deficient.

Vitamin D is called the sunshine vitamin for good reason. The body needs only a few minutes of direct sunlight to generate amounts that are more than adequate. With age, however, skin becomes less efficient at producing vitamin D, so older adults are particularly vulnerable to this deficiency. Vitamin D levels can be measured by blood tests.

“The majority of older adults in the U.S. have deficient levels of vitamin D,” says Llewellyn, “and our findings suggest that this may increase the risk of new cognitive problems and dementia.”

Researchers have begun to think vitamin D is important to brain health by protecting the blood supply to the brain, Llewellyn said at the Alzheimer’s conference Sunday.

“We also suspect that vitamin D may help to clear toxins from the brain,” Llewellyn says, helping to break down amyloid-beta protein, the substance that is thought to play a role in causing Alzheimer’s disease.

A related report published Monday by some of the same researchers in the Archives of Internal Medicine had similar results. Analyzing data from another study that attempts to identify factors that lead to disability, Llewellyn and colleagues found that older men and women with low levels of vitamin D don’t do as well on tests of reasoning, learning and memory as those with higher levels. Participants completed interviews about their health history, had medical examinations, provided blood samples and took tests measuring thinking skills at the start of the study and again after three years and six years.

The analysis reveals that compared with participants who had sufficient vitamin D levels, those who were severely deficient experienced a substantial decline in thinking and in executive function—the ability to organize thoughts, make decisions and plan ahead. The authors say that the link between vitamin D deficiency and cognitive decline persisted even after adjusting for diet, health and other factors.

“This work suggests an additional potential benefit to maintaining adequate vitamin D levels,” says Edward Giovannucci, M.D., of Harvard’s School of Public Health, who was not involved in the report, “and it’s important that deficiency is treated, as low levels are detrimental to overall health.” However, he adds, further study is needed to clarify the role of vitamin D in brain function.

Nissa Simon writes about health issues and lives in New Haven, Conn.

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