By Robby Berman — Fact checked by Jennifer Chesak
An estimated 6 million people live with Alzheimer’s disease (AD) in the United States.
That number is set to grow to 13 million by 2050 due to the country’s aging population. Alzheimer’s disease is also the sixth leading cause of death in the U.S.
Every 65 seconds, someone develops AD, and 60% to 80% of people with dementia have AD. Alzheimer’s affects memory, thinking, and, as a result, behavior as it progresses. While it is most often a disease of people 65 and older, early onset of AD can strike people in their 40s and 50s.
The possible causes of dementias, including AD, remain somewhat elusive and are an area of ongoing research.
Recently, a new, observational study investigates for the first time the presence of vitamin D in the brain and its potential effect on cognitive outcomes.
The study found that better cognitive function is associated with people who have higher concentrations of vitamin D in their brains. Before the study, it had been unclear whether vitamin D was present in the brain at all.
Lead author Kyla Shea, Ph.D., a researcher at Tufts University in Massachusetts specializing in the role of micronutrients in age-related disease and disability, told Medical News Today:
“A number of studies reported higher blood vitamin D levels were associated with less cognitive decline or lower risk of dementia. Even though these studies suggested associations, it was possible the blood levels were markers of something else because we did not know if vitamin D was even present in the human brain.”
Studying vitamin D and cognitive function
For the study, researchers analyzed data for 290 deceased individuals who had participated in the Rush Memory and Aging Project until their deaths.
None had dementia at first enrollment, and all were older, community-dwelling individuals. Participants’ cognitive health was measured throughout the study, and they agreed to donate their organs upon death.
The researchers found that higher brain vitamin D concentrations in all four brain areas were associated with a 25% to 33% lower chance of developing dementia or mild cognitive impairment by the time of individuals’ last visit before death.
Thomas H. J. Burne, Ph.D., associate professor of developmental neurobiology at the University of Queensland, Australia, not involved in the study, told MNT:
“The study is certainly very novel. I have not previously seen data on blood and brain vitamin D levels in people that have been monitored prior to disease onset. This is a valuable data set, and may offer valuable insights.”
Dr. Burne noted that as an observational study, the findings “at best [are] likely to reveal correlations and not underlying causal mechanisms.” He also pointed out that since participants were all within the range of normal vitamin D levels, the study did not look at associations between insufficient levels of vitamin D and cognitive function.
In addition, the authors of the study note another possible interpretation of their findings.
They wrote that it’s possible that concentrations of vitamin D in the brain could be an indicator of “cognitive resilience” and that people with higher vitamin D levels may exhibit “fewer signs of cognitive impairment despite a high neuropathological burden.”
Another limitation of the study is that most participants were white. The researchers cite a need for future studies of more diverse populations.
Vitamin D and pathology markers
The researchers tracked levels of a form of vitamin D, 25(OH)D3 in the brain.
They assessed vitamin D in the mid-temporal cortex, mid-frontal cortex, cerebellum, and anterior watershed white matter of the brain, all of which have been implicated in different types and stages of dementia, including AD and dementia with Lewy bodies.
Dr. Burne cited concerns about the difficulty in taking accurate measurements of 25(OH)D3 in “such a lipid-dense tissue.” He added that the study was unclear about whether participants were receiving supplements, which he said may alter the interpretation of the data.
What’s more, the study found no correlation between vitamin D levels and amyloid plaques, which were previously thought to be among the potential causes of AD. But researchers are still studying any association between amyloid plaques and AD due to an ongoing lack of consensus on the theory.
“Amyloid buildup does not appear to be causal for dementia or cognitive impairment, which may explain the large failure rate of clinical trials aiming to treat amyloid,” Dr. Burne said. “Therefore, it is no surprise to me that there is no association between vitamin D and amyloid.”
In addition, researchers observed no sign of an association with Lewy bodies, suggesting that vitamin D is not linked to Lewy body dementia. They also did not find a link between vitamin D, white matter lesions, or signs of mini-stroke.
“Our current research is moving toward vascular dementia, for which there is evidence of biological plausibility,” Dr. Shea said.
How vitamin D affects the brain
The role that vitamin D plays in cognition is not fully understood. But this is the first study to look at vitamin D levels in the brain and the potential association with cognitive outcomes.
Dr. Shea noted that it seems vitamin D is involved in cell-signaling pathways that may be part of neurodegeneration.
However, neurodegeneration is complex and not well-understood.
“There are no studies that have shown a causal relationship between vitamin D deficiency and cognitive impairment, but many that show a correlation,” Dr. Burne noted, citing a 2019 mouse study he conducted as one example.
Dr. Burne added that vitamin D deficiency is linked to a “reduced hippocampal volume and disrupted structural connectivity in patients with mild cognitive impairment.”
Getting your daily dose of vitamin D
Most people in the U.S. have adequate levels of vitamin D, according to the National Institutes of Health.
Most children and adults from ages 1 to 70 require 15 micrograms or 600 individual units of vitamin D each day. Infants under 1 require 10 mcg (400 IUs) and adults over 70 need 20 mcg (800 IUs).
But if you’re one of the 1 in 4 people with vitamin D deficiency, your doctor can tell you how much vitamin D supplementation you need.
If you’re unsure whether you’re getting enough vitamin D, you can ask your doctor to measure your vitamin D levels in a blood test.
This article originally appeared here and was republished with permission.