NEW YORK — A study has found no connection between vitamin D deficiency and the development of dementia.

A study by the University of California, San Diego found that people who are deficient in vitamin D are twice as likely to develop dementia than people who get enough of the vitamin, which has been linked to neurodegenerative disease.

Researchers from UC San Diego, Harvard Medical School and the University at Buffalo looked at more than 4,000 individuals from more than 70 countries, and found that those who reported being vitamin D deficient had an increased risk of developing dementia, as did those who were vitamin D-sufficient.

The study was published online Wednesday in the journal JAMA Psychiatry.

It also found no relationship between vitamin-D deficiency and Alzheimer’s disease or other forms of dementia, the authors said.

The finding raises concerns about vitamin D’s impact on health, said lead author Steven J. Cawthon, a UC San Marcos postdoctoral fellow in the Department of Epidemiology.

“Vitamin D deficiency is a major public health issue,” he said.

“We need to understand the causes and mechanisms of vitamin D deficiencies.”

Cawthyon and colleagues looked at the levels of vitamin-E and vitamin-B12 in blood samples from 1,843 people, mostly older adults, who had no dementia or Alzheimer’s.

The researchers then followed those who had died or were dying and examined their brain tissue for markers of vitamin A, vitamin D and other nutrients.

Vitamin-A levels were lower in those who did not have dementia or were vitamin-sufficient, and the researchers found that the higher levels of vitamins A and D were associated with less dementia risk.

Vitamin D was also associated with lower risk of other forms, including Alzheimer’s and Huntington’s disease, but it was not a significant risk factor for dementia, according to the study.

Vitamin B12 levels were higher in those with dementia or those with more than one form of dementia and were lower than in those without dementia or in those not taking any vitamin D supplements.

The findings are consistent with findings from previous studies, said Cawthington, who is now a postdoctoral researcher at the University Hospital in Bremen.

“This is one of the largest randomized controlled trials to date on vitamin D in relation to dementia,” he told The Associated Press.

“What we found is there is no evidence of an association between vitamin A deficiency and cognitive decline or Alzheimer disease or any other type of dementia.”

He said the findings could have important implications for people with chronic diseases such as diabetes, which are linked to dementia.

Cawsong said the study does not prove that vitamin D causes dementia.

“I don’t think we can say that this is the cause of dementia,” Caw thon said.

He said researchers are still investigating the mechanisms that are involved in the development and progression of dementia in people with vitamin D levels too low.

The results are “really exciting” and will likely lead to new studies, Cawong said.

Cawny, of the University Health Network, said the research is important because it suggests vitamin D is important for brain health.

“It’s a really important issue and one that we need to continue to explore,” he added.

Researchers will also examine the possible impact of vitamin supplementation on dementia.

Researchers hope that the findings will lead to better guidelines for the supplementation of vitamin supplements, Cawnington said.

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