Older adults with low levels of vitamin D appear more likely to experience declines in thinking, learning and memory over a six-year period, according to a report in the July 12 issue of Archives of Internal Medicine, one of the JAMA/Archives journals. An estimated 40 percent to 100 percent of older adults in the United States and Europe are deficient（缺乏，欠缺） in vitamin D, according to background information in the article. This deficiency has been linked to fractures（骨折，断裂） , various chronic diseases and death. Vitamin D may help prevent the degeneration of brain tissue by having a role in formation of nervous tissue, maintaining levels of calcium in the body, or clearing of beta-amyloid（淀粉体） , the substance that forms the brain plaques（斑块，瓷片） and tangles（缠结，服饰） associated with Alzheimer's disease.

David J. Llewellyn, Ph.D., of University of Exeter, England, and colleagues assessed blood levels of vitamin D in 858 adults who were age 65 or older when the study began in 1998. Participants completed interviews and medical examinations and provided blood samples. At the beginning of the study and again after three and six years, they repeated three tests of cognitive function—one assessing overall cognition, one focusing on attention and one that places greater emphasis on executive function, or the ability to plan, organize and prioritize（区分优先次序） .

Participants who were severely deficient in vitamin D (having blood levels of 25-hydroxyvitamin D of less than 25 nanomoles per liter) were 60 percent more likely to have substantial cognitive decline in general over the six-year period and 31 percent more likely to experience declines on the test measuring executive function than those with sufficient vitamin D levels. "The association remained significant after adjustment for a wide range of potential confounders and when analyses were restricted to elderly subjects who were non-demented at baseline," the authors write. However, no significant association was seen for the test measuring attention.

"If future prospective studies and randomized controlled trials confirm that vitamin D deficiency is causally related to cognitive decline, then this would open up important new possibilities for treatment and prevention," the authors conclude.

(Arch Intern Med. 2010;170[13]:1135-1141. Available pre-embargo to the media at www.jamamedia.org.)

Editor's Note: Please see the article for additional information, including other authors, author contributions and affiliations, financial disclosures（财务披露） , funding and support, etc.