Does Vitamin D Prevent Dementia? Here’s What You Need to Know

By Simon Spichak, MSc | July 25th, 2022

A large 2022 study found a link between vitamin D deficiency and dementia risk. But hang on: Here's why you shouldn't be rushing to the vitamins and supplements aisle.  

About one in 20 Americans have levels of vitamin D that would qualify them as deficient. A deficiency of vitamin D has been linked to several medical conditions and disorders, and now there’s another addition to the list: dementia.

An observational study published in The American Journal of Clinical Nutrition investigated the relationship between levels of the precursor to vitamin D, brain volume and brain health, analyzing data from nearly 300,000 people and concluded that those with a deficiency were almost twice as likely to develop dementia to those with normal D levels. The researchers also found a genetic link between this vitamin and dementia risk. 

More than 70 published news articles covered the study, with a number of those headlines stating or implying that the study found not only that vitamin D deficiency causes dementia, but that vitamin D — through supplements or sunlight — could prevent it. In fact, neither of these things are the case.

Professor Elina Hyppönen from the University of South Australia, who led the study, said that the findings are, nonetheless, important for dementia prevention. “In this UK population, we observed that up to 17 percent of dementia cases might have been avoided by boosting vitamin D levels to be within a normal range,” Hyppönen said. However, while the study found that individuals with very low levels of the vitamin precursor are at the highest risk for developing dementia, it did not look at why these levels were so low.

The team also didn’t track these individuals over time. Without doing these things, this study can’t answer the question as to whether  providing D-deficient study participants with vitamin D would have lowered their risk of developing dementia.

There hasn’t been research to determine that D deficiency and dementia aren’t both causes of some unknown third factor: These findings don’t establish such a deficiency can cause dementia — and likewise, they don’t establish that giving your body more vitamin D can keep neurodegenerative disease at bay.

What’s more, while time outdoors is generally good for one’s health, supplements, in some cases, may not be. Experts say it is important to note that some supplements are loaded with several times the amount of vitamin D your body needs each day. Taking vitamin D that far exceed the recommended daily amount can lead to nausea, vomiting, muscle weakness, confusion, dehydration — even hospitalization. 

Additionally, scientists have conducted clinical trials to test whether the vitamin could prevent the risk of developing Alzheimer’s or other dementias. Two systematic reviews, both which compiled all of these clinical trials together, didn’t find sufficient evidence to show that vitamin D has any protective effect against dementia.

According to Dr. Thomas Carpenter, a pediatric endocrinologist from Yale Medicine, the population his team most often sees a D deficiency in is breastfed infants, particularly in wintertime.

If you feel fatigued and concerned that you’re not getting enough vitamin D, visit your doctor’s office to check if you’re deficient. Otherwise you can keep your risk of dementia low by staying active and eating a healthy diet.

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