New Study Finds 'Healthy' Levels of This Vitamin Are Linked To Cognitive Decline

How to make sure you're getting enough.

Kass

Mar 1, 2025 - 21:04

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New Study Finds 'Healthy' Levels of This Vitamin Are Linked To Cognitive Decline

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Registered Dietitian Nutritionist

By Molly Knudsen, M.S., RDN

Registered Dietitian Nutritionist

Molly Knudsen, M.S., RDN is a Registered Dietician Nutritionist with a bachelor’s degree in nutrition from Texas Christian University and a master’s in nutrition interventions, communication, and behavior change from Tufts University. She lives in Newport Beach, California, and enjoys connecting people to the food they eat and how it influences health and wellbeing.

Image by Diamond Dogs / istock

March 01, 2025

There’s no doubt that nutrient deficiencies greatly affect our long-term health. Vitamin D deficiencies have been linked to osteoporosis, fractures, and diabetes. Low magnesium levels can even increase the risk of heart disease. And a vitamin B12 deficiency is associated with cognitive conditions.

However, researchers of a recent study had a hunch that avoiding vitamin B12 deficiency wasn’t enough to fully protect the brain from cognitive decline. They found that normal blood levels of this nutrient are linked to cognitive decline in older adults.

Let’s break down why that is and how to make sure you’re actually getting enough of this key vitamin.

What to know about vitamin B12 levels

Vitamin B12 levels are measured by a blood test, with levels below 148 pmol/L indicating a deficiency. It’s estimated that about 6% of adults over 60 have a true vitamin B12 deficiency. The normal range for vitamin B12 levels is typically considered to be 148-664 pmol/L.

The thing is, vitamin B12 levels exist in the blood in two different forms: An inactive form and an active form.

The body is only able to use the active form of the vitamin—for processes like energy production, DNA synthesis, and proper brain function—whereas inactive vitamin B12 is either taken to the liver for storage or recycling or excreted altogether.

Low levels of active B12 are linked to slower processing

So in this new study, researchers gathered data on vitamin B12 levels of 231 healthy participants in their 60s and 70s and had them complete various cognitive performance tests. MRI brain scans were also taken.

Overall, the average vitamin B12 levels for this group were far from the deficiency cut-off at 414.8 pmol/L.

They found that people with lower levels of B12, especially low levels of active vitamin B12, had much slower processing speeds.

And, further cognitive analysis revealed:

Low active B12 levels were also linked to slower vision-related nerve signaling. Those with low active B12 levels had more white matter hyperintensities in the brain—indicating damage to tiny blood vessels in the brain. This can reduce blood flow to the brain, and these areas are linked to impaired cognition. People with especially high levels of inactive vitamin B12 had higher serum tau levels. High levels of serum tau are a known risk factor for Alzheimer’s disease and stroke.

These are particularly concerning findings especially with participants having vitamin B12 levels within the recommended range. However, that range is not necessarily indicative of better health or decreased cognitive impairment risk if a person has lower levels of the active vitamin.

How to increase levels of active vitamin B12

Inactive B12 often indicates a lack of sufficient or properly functioning B12 transportation in the body or storage.

And no matter your age (if you’re in your 20s or 70s), there are a handful of things you can do to make sure you’re getting enough vitamin B12, and that your body can actually use it.

Eat high-quality animal proteins: Vitamin B12 is only found in animal products like meat, poultry, seafood, eggs, and dairy. You don’t have to eat a carnivore diet to get enough B12, but adding a few servings of these readily absorbable proteins to your day is a good choice for your vitamin B12 levels. And it’ll also help you reach your protein needs. Incorporate a methylated vitamin B12 supplement: Supplementation with vitamin B12 is needed for those who are vegan and vegetarian, and it’s also a smart choice for pretty much everyone. But, not all B12 supplements are created equal. You always want to choose one with a methylated source of the vitamin like methylcobalamin. This form of vitamin B12 is already active and ready for the body to use. Many multivitamins include vitamin B12 and we rounded up our favorites here (which include those with methylcobalamin). Talk to your doctor about medical conditions: There are a few clinical reasons why your vitamin B12 levels may be subpar. It could be a result of low stomach acid 1, inflammatory gut conditions, or medicines (like metformin or antacids). If any of these scenarios apply to you, it’s best to speak with your healthcare provider to address these absorption issues.

The takeaway

Vitamin B12 has so many crucial roles in the body including cognition. While blood tests can help determine true deficiencies in nutrients, the normal range may not be precise enough to indicate optimal health or even disease risk.

To help make sure you’re getting enough vitamin B12, increase your dietary intake and consider a supplement.