People who have higher vitamin D levels as they enter middle age might have a reduced risk of developing dementia, a new study suggests.
For the study, researchers measured vitamin D blood levels for about 800 adults without dementia, who were 39 years old on average when the study began. Then, about 16 years later when people were in their mid-fifties, participants had PET scans of their brains to measure the accumulation of tau and beta-amyloid proteins, substances tied to greater dementia risk.
Researchers found that adults with higher vitamin D levels at the start of the study had lower levels of tau protein on brain scans taken later in middle age, according to findings published in the journal Neurology Open Access.
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“Vitamin D may play an important role in preventing, or slowing down, changes of Alzheimer’s disease and dementia in the brain,” says the senior study author, Emer McGrath, MB, PhD, an associate professor of medicine at the University of Galway and a consultant neurologist at Galway University Hospital in Ireland.
“Vitamin D may have beneficial effects by reducing inflammation in the brain, exerting antioxidant effects, and reducing the collection of abnormal tau protein in the brain,” Dr. McGrath says.
Higher Vitamin D Levels Were Associated With Less Tau Buildup
Participants had an average vitamin D blood level of 38 nanograms per milliliter (ng/mL). Researchers defined measurements below 30 ng/mL as low, and about a third of participants fell into this group.
Compared to those with low vitamin D levels, participants with high vitamin D levels had less tau buildup in their fifties, including in regions of the brain where this protein tends to accumulate first in individuals who develop dementia, the study found.
The connection between high vitamin D levels and reduced tau buildup remained strong even after researchers accounted for several factors that can impact this association, including age, sex, the exact amount of time that passed between the vitamin D test and the brain scans, the time of year vitamin D got tested, and health issues that can independently lead to tau accumulation.
But the study didn’t find a link between midlife vitamin D levels and later amyloid buildup. The researchers said it’s possible this is because tau buildup starts earlier in the progression of dementia, and at younger ages than amyloid buildup.
The Study Has Some Limitations
The study wasn’t a controlled experiment designed to prove whether or how specific vitamin D levels might directly prevent or slow the progression of dementia.
One limitation of the study is that participants were predominantly white, making it possible that the results might not apply to people from other racial or ethnic groups.
Another drawback is that researchers looked at vitamin D levels at a single point in time, making it impossible to determine how any changes in vitamin D levels over the years might impact future dementia risk.
In addition, only 22 people were taking vitamin D supplements at the start of the study, which makes it impossible to determine how supplementation might impact future dementia risk.
Even so, the study adds to the evidence that vitamin D levels might be one potential risk factor for dementia that people can control, McGrath says.
“Our results suggest that low levels of vitamin D in midlife may be a potential modifiable target to reduce risk of dementia later in life,” McGrath says. “However, our results do not prove that [lack of] vitamin D causes dementia. Further studies will be required before we could recommend routine vitamin D checks in the community.”
How to Maintain Good Vitamin D Levels
Most people don’t need supplements to maintain healthy vitamin D levels, says Helen Lavretsky, MD, a geriatric psychiatrist, a professor, and the director of research at the Integrative Medicine Collaborative at the University of California in Los Angeles.
“The best way to maintain healthy vitamin D3 levels is through a combination of safe sunlight exposure and dietary intake of fatty fish such as salmon, trout, mackerel or herring, cod liver oil, egg yolks, and fortified foods like milk, orange juice, and cereals,” says Dr. Lavretsky, who wasn’t involved in the study.
Just 10 to 30 minutes of midday sun twice a week may be ideal for absorbing enough vitamin D, Lavretsky adds. But some people who have darker skin or who don’t get much sun exposure due to their climate or the season may want to consider daily vitamin D3 supplements in low doses, around 600 to 800 international units (IUs), Lavretsky adds.
Should You Get Your Vitamin D Levels Checked?
“Routine vitamin D testing is not recommended for the general, healthy population,” Lavretsky says.
Instead, it should be reserved for people at high risk for vitamin D deficiency, like people who get limited sun exposure, those with darker skin, or those who are at higher risk for health issues related to low vitamin D. This group includes individuals with obesity, people older than 65, and those with osteoporosis, Lavretsky says.
She also recommends women get vitamin D levels checked around the time that they go through menopause. The rapid drop in estrogen that occurs during this transitional period can reduce bone density, and vitamin D is important for maintaining stronger bones, she says.
When it comes to dementia prevention, though, there isn’t enough evidence to support monitoring vitamin D levels at this time, Lavretsky says.
“It’s still unclear how much raising vitamin D actually reduces dementia risk,” Lavretsky says.
