Vitamin D in the brain could help people function better as they age

“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 Sarah Booth, senior and corresponding author of the study, 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.

Importance of vitamin D

Vitamin D is a nutrient that is fat soluble, meaning that it can be stored in the body and also helps to absorb calcium. Unlike water-soluble vitamins, vitamin D does not dissolve with water and needs to be paired with fat to be absorbed by the body.

The vitamin helps in the development of teeth and bone by allowing for the absorption of calcium and phosphorus. It helps with immune responses as well. However, now researchers know that it may potentially have another benefit that helps the aging brain. The nutrient can be found in foods such as fatty fish and drinks such as milk or orange juice.

The first study of its kind

The research was the first to show that vitamin D is present in the brain and has a profound effect on it, in a positive way. It is not the first research to study the link between diet, vitamin D and cognitive performance, but it’s the first to link the concentrations of vitamin D to possible cognitive decline.

“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,” stated Kyla Shea, lead author on the study, 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,” she continued.

The research

The research team studied samples of brain tissue from 290 individuals in the Rush Memory and Aging Project, a long-term study of Alzheimer’s disease that began 25 years ago. The team at Rush University in the U.S. then evaluated the cognitive function of the participants in the study.

They did this by analyzing the aging participants with no sign of cognitive impairment and studied as they aged. The team looked for any irregularities or abnormalities in the individuals after death.

Key discoveries

In the study, the researchers from Tuft University looked for vitamin D in four parts of the brain, with two of the regions linked to Alzheimer’s disease, one connected to forms of dementia linked to blood flow and the final region that didn’t have any link to cognitive decline.

The researchers made two unprecedented discoveries. First, they revealed that vitamin D was present in brain tissue. “We now know that vitamin D is present in reasonable amounts in human brains, and it seems to be correlated with less decline in cognitive function,” Shea said. The second factor they noticed was that high levels of vitamin D in the four regions of the brain contributed to better cognitive function and health.

The study was published in the journal Alzheimer's & Dementia: The Journal of the Alzheimer's Association.

In the future the team plans on studying the correlation between vitamin D and its role in the brain. “Vitamin D could be related to outcomes that we didn’t look at yet, but plan to study in the future,” Shea stated. The study can help researchers find strategies and potential treatments for people who have neurodegenerative diseases such as Alzheimer’s.

Abstract: Evidence is accumulating that nutritional strategies play a key role in delaying or preventing the onset of cognitive decline and dementia, either through directly affecting neuropathology or by fostering resilience to pathology. One nutritional factor that has received considerable attention is vitamin D, an essential fat-soluble vitamin and pro-hormone acquired through diet and sun exposure. The 1α-hydroxylase enzyme (cytochrome P450 [CYP]; CYP27B1) is required to convert 25-hydroxyvitamin D3 (25(OH)D3), the main circulating form of vitamin D, to the biologically active 1,25-dihydroxyvitamin D (1,25(OH)2D), the form that binds to the nuclear vitamin D receptor (VDR) to exert its biological function. The resultant vitamin D signaling in the brain is purportedly involved in neurodegeneration. Several epidemiological studies have associated low vitamin D intake or circulating levels with cognitive decline and dementia. Whether low vitamin D represents an independent risk factor for cognitive decline and dementia is controversial. Some randomized-controlled trials have tested the effect of vitamin D supplementation on cognitive performance, some with reported null findings. However, the limitations of these trials include not being designed to study cognitive decline as a primary outcome and/or studying participants who are not necessarily at risk for cognitive decline or vitamin D insufficiency. The observation of change in cognitive performance has often been limited to a period of <3 years. Important outstanding questions remain including: (1) are brain levels of vitamin D metabolites associated with cognitive decline or underlying neuropathologies; and (2) do circulating 25(OH)D levels reflect the vitamin D in the human brain? The purpose of this study was to analyze human brain concentrations of vitamin D and related metabolites and determine the associations with ante-mortem measures of cognitive function and postmortem neuropathologic outcomes in participants of the Rush Memory and Aging Project (MAP).