Low Levels Of This Vitamin Were Linked To A 33% Higher Dementia Risk
Vitamin B12 is best known for its role in energy metabolism, red blood cell formation, and nerve function—but growing research suggests this essential nutrient may also play a role in healthy aging.
Now, a large observational study1 adds to the evidence linking low vitamin B12 status with brain health outcomes. Researchers found that adults over age 50 with lower B12 levels were more likely to develop dementia, mild cognitive impairment, stroke, and other neurocognitive conditions compared to those with vitamin B12 levels in the normal range.
Here's what you need to know about B12 and dementia.
About the study
Researchers wanted to find out whether consistently low vitamin B12 levels (not just one unusually low test result) were linked to a higher risk of cognitive decline and dementia over time. They analyzed electronic health record data from the TriNetX Global Collaborative Network, including more than 258,000 adults ages 50 and older.
Participants were divided into two groups based on their vitamin B12 measurements:
- Low vitamin B12 status: Two measurements below 300 pg/mL within a two-year period
- Reference group: Two measurements between 300 and 900 pg/mL
After matching participants based on similar characteristics, researchers followed both groups for up to 10 years to track the development of dementia and other health outcomes.
Low vitamin B12 levels were associated with a 33% higher dementia risk
Results showed that compared to people with higher B12 levels, those with low vitamin B12 status had a:
- 33% higher risk of developing all-cause dementia
- 33% higher risk of mild cognitive impairment
- 31% higher risk of stroke
- 23% higher risk of all-cause mortality
The researchers also found similar associations across dementia subtypes, including Alzheimer’s disease and vascular dementia.
When looking specifically at people with vitamin B12 deficiency (defined as levels below 200 pg/mL), the association was even stronger: These individuals had a 64% higher risk of developing dementia compared to those with healthier B12 levels.
Why B12 matters for the brain and who's most at risk
Vitamin B12 is involved in several processes that are important for maintaining a healthy nervous system.
One key role is helping regulate homocysteine, an amino acid that, when elevated, has been associated with increased inflammation and vascular damage. Vitamin B12 works alongside folate and vitamin B6 to help convert homocysteine into other compounds the body can use.
Low B12 levels may also affect:
- Myelin production: The protective coating around nerve fibers that helps support efficient communication between brain cells
- DNA synthesis and repair: Processes needed for healthy cell function
- Neurotransmitter production: Chemical messengers involved in mood, memory, and cognition
Because the brain and nervous system rely heavily on these pathways, researchers have long been interested in whether inadequate B12 status could contribute to cognitive decline.
Who is most at risk for low vitamin B12?
Vitamin B12 deficiency becomes more common with age, partly because some adults produce less stomach acid, which is needed to absorb B12 from food.
Certain groups may also be more likely to have inadequate levels, including:
- Older adults: The stomach produces less acid with age, and that acid is what helps release B12 from food so your body can absorb it
- People taking certain medications: Metformin (a common diabetes medication) and long-term use of acid-reducing medications like proton pump inhibitors or H2 blockers can interfere with B12 absorption
- Vegans and vegetarians: B12 is found almost exclusively in animal-derived foods, so people who avoid them are at higher risk without supplementation
- People with digestive conditions: Conditions like celiac disease or Crohn's disease can affect how well the gut absorbs nutrients, including B12
Signs your B12 might be low
B12 deficiency can be easy to miss. Its symptoms, including persistent fatigue, brain fog, tingling or numbness in the hands or feet, mood changes, and a smooth or unusually sore tongue, tend to develop gradually and overlap with a lot of other common issues.
If unexplained fatigue is part of the picture, B12 is one of the first things worth ruling out. A simple blood test can check your levels, and if you fall into one of the higher-risk groups above, it's worth asking your doctor about routine monitoring.
How to get enough B12
You can get vitamin B12 through food and supplements.
- Through food: The best sources are animal-based: meat, fish, shellfish, eggs, and dairy. Fatty fish like salmon and sardines, beef liver, and clams are especially rich in B12. If you eat little or no animal products, fortified foods (certain plant milks, cereals, nutritional yeast) can help fill the gap, though a supplement is often still the most reliable option.
- Through supplementation: If you're in a higher-risk group, a supplement is often the most practical move. Vitamin B12 supplements come in several forms, including methylcobalamin (a methylated form of B12) and cyanocobalamin. Methylcobalamin is a naturally occurring form of vitamin B12 that the body can use directly.
The takeaway
B12 deficiency is common, easy to test for (although not frequently tested), and often correctable, which makes it stand out among the many factors researchers are studying in relation to brain health.
This research adds meaningful weight to the case for paying attention to your B12 status, particularly as you get older. If you haven't had your levels checked recently, it's a simple conversation worth having with your doctor.