An estimated 55 million people worldwide live with dementia, a number that's expected to rise as the global population ages. To find treatments that can slow or stop the disease, scientists need to better understand the factors that can cause dementia.
Researchers at Tufts have completed the first study examining levels of vitamin D in brain tissue, specifically in adults who suffered from varying rates of cognitive decline. They found that members of this group with higher levels of vitamin D in their brains had better cognitive function. The study was published December 7 in Alzheimer's & Dementia: The Journal of the Alzheimer's Association.
"This research reinforces the importance of studying how food and nutrients create resilience to protect the aging brain against diseases such as Alzheimer's disease and other related dementias," said senior and corresponding author Sarah Booth, director of the Jean Mayer USDA Human Nutrition Research Center on Aging (HNRCA) at Tufts and lead scientist of the HNRCA's Vitamin K Team.
Vitamin D supports many functions in the body, including immune responses and maintaining healthy bones. Dietary sources include fatty fish and fortified beverages (such as milk or orange juice); brief exposure to sunlight also provides a dose of vitamin D.
"Many studies have implicated dietary or nutritional factors in cognitive performance or function in older adults, including many studies of vitamin D, but all of them are based on either dietary intakes or blood measures of vitamin D," said lead author Kyla Shea, a scientist on the Vitamin K Team and an associate professor at the Friedman School of Nutrition Science and Policy at Tufts. "We wanted to know if vitamin D is even present in the brain, and if it is, how those concentrations are linked to cognitive decline."
Booth, Shea, and their team examined samples of brain tissue from 209 participants in the Rush Memory and Aging Project, a long-term study of Alzheimer's disease that began in 1997. Researchers at Rush University assessed the cognitive function of the participants, older people with no signs of cognitive impairment, as they aged, and analyzed irregularities in their brain tissue after death.
In the Tufts study, researchers looked for vitamin D in four regions of the brain-two associated with changes linked to Alzheimer's disease, one associated with forms of dementia linked to blood flow, and one region without any known associations with cognitive decline related to Alzheimer's disease or vascular disease. They found that vitamin D was indeed present in brain tissue, and high vitamin D levels in all four regions of the brain correlated with better cognitive function.
However, the levels of vitamin D in the brain didn't associate with any of the physiological markers associated with Alzheimer's disease in the brain studied, including amyloid plaque buildup, Lewy body disease, or evidence of chronic or microscopic strokes. This means it's still unclear exactly how vitamin D might affect brain function.
