The Shocking Connection Between Vitamin D and Dementia Risk

When the National Health and Nutrition Examination Surveys (NHANES) monitored the vitamin D status of more than 71,000 Americans from 2001-2018, results showed that:

6 percent had severe vitamin D deficiency

22 percent had moderate vitamin D deficiency

6 percent had some level of vitamin D insufficiency

In other words, just over one-third (34.5 percent) of people studied had sufficient levels of vitamin D. Severe and moderate deficiencies were more common during the wintertime, as well as among certain populations—females, non-Hispanic black populations, and individuals ages 20-29.

Overall, the most significant predictors of severe vitamin D deficiency were: age, sex, ethnicity, season, sun-protective behaviors, lower BMI, lower socioeconomic status, drinking alcohol, and less milk consumption.

These numbers echo the findings at Amen Clinics. All patients receive vitamin D tests, and a surprising number of them have low levels. Modern lifestyle choices, like sunscreen application and less time spent outdoors, have diminished vitamin D levels.

Therefore, it’s a good idea to check your vitamin D levels the next time you visit a doctor. A simple blood test, called 25-hydroxyvitamin D level, will let you know where you fall in the range of results:

Deficient: <30 ng/mL (nanograms per milliliter)

Low-Normal: 30-50 ng/mL

Normal: 30-100 ng/mL

Optimal: 50-100 ng/mL

Ensure you receive the actual number of your result—not just the category it falls in (such as “normal”). You want to reach the optimal range to offer the best protection against a range of health issues.

Low levels of vitamin D have been associated with more than 200 conditions, from depression and dementia to autism and heart disease. On the other hand, optimal levels will support both physical and mental health in numerous ways.

Numerous studies have linked vitamin D to effects on the brain. A 2014 study found that vitamin D prevented cognitive decline and enhanced the synaptic function in the hippocampus of aging rats. Those given higher vitamin D3 diets were able to perform complex memory tasks, unlike rats with low or normal dietary amounts of vitamin D.

That’s because, as the study noted, vitamin D helps regulate calcium and is responsible for diverse functions in various tissues, including the brain. The authors cited increasing evidence associating vitamin D with maintaining cognitive function (and its deficiency with accelerated cognitive decline with age).

These findings have been echoed in human studies, too. A 2022 study linked vitamin D with better cognitive function. Subjects with higher brain concentrations of vitamin D showed 25-33 percent lower odds of dementia or mild cognitive impairment (MCI) before death.

Similarly, research from 2015 determined that those with deficiencies in vitamin D had greater rates of decline in episodic memory and executive function, compared to those with adequate levels. And participants with MCI had lower levels of vitamin D than those who were cognitively healthy.

These findings backed up an earlier study, published in the journal Neurology in 2014, that tracked 1,658 people over the age of 65 over an average of six years.

Researchers found that not getting sufficient vitamin D may more than double the risk of developing dementia in older populations—a 53 percent increase. And those who were severely deficient had a 125 percent increased risk, compared to participants with normal vitamin D levels.

These results were similar when looking at Alzheimer’s disease. Participants with lower levels of vitamin D were nearly 70 percent more likely to develop Alzheimer’s. Severe deficiency was associated with a 120 percent increase in the likelihood of developing the disease.

The links illustrated above are not surprising, because we know that vitamin D receptors are present throughout the brain. Vitamin D plays a crucial role in protecting cognitive function, learning, and making memories.

A study published in the Journal of Alzheimer’s Disease points to another possible reason for the link between cognitive decline and vitamin D. It suggested that vitamin D may stimulate the immune system, helping rid the brain of beta-amyloid, which are the plaques seen in Alzheimer’s disease.

What does this mean about the connection between vitamin D and Alzheimer’s disease? If low vitamin D is linked to dementia risk and cognitive decline, researchers were quick to ask: Does vitamin D prevent dementia? And could vitamin supplements help?

A Canadian study published in 2023 explored this link between vitamin D supplementation and dementia in 12,388 individuals who did not have dementia. Researchers reported that “vitamin D exposure was associated with significantly longer dementia-free survival and lower dementia incidence rate than no exposure.”

Furthermore, in 2024, a systematic review of literature explored the potential relationship between vitamin D deficiency and risk of cognitive impairment or dementia. The resulting meta-analysis considered 23 studies on the subject.

Results showed that vitamin D deficiency was associated with a higher risk for dementia (1.42 times the risk) and a 34 percent elevated risk for cognitive impairment. But vitamin D was non-linearly related to dementia risk, meaning that benefits peak at a certain level.

This review established optimal vitamin D levels at 77.5-100 nmol/L vitamin D for reducing dementia risk and >40.1 nmol/L for decreasing risk of Alzheimer’s disease.

Maintaining optimal vitamin D levels won’t only protect your brain from dementia—it will boost your mood, promote mental health, and improve your immunity. Here are three ways to make sure you’re getting enough of this crucial vitamin:

Mind your diet. Load up on foods rich in vitamin D. These include mushrooms, fatty fish (such as salmon and tuna), and eggs (especially yolks).

Bask in the sun. While too much sun exposure can be harmful, you’ll want to aim for getting some sun (without sunscreen) in short bursts. Go outside twice a week for 5-30 minutes to activate vitamin D production.

Take a supplement. Vitamin D supplements are helpful to ensure your levels are optimal. This is especially important in winter months, when full sun exposure is less available. Try to add 2,000-5,000 IU of vitamin D3 per day to your system through high-quality supplements.

In this video, Amen Clinics integrative nutritionist Cindy Santa Ana reveals the other nutritional supplements your body needs to fully activate vitamin D.