The latest research in the Annals of Neurology suggests that even B12 levels considered "normal" may still be linked to neurological damage.
The study on people with B12 levels above the current deficiency threshold, yielded evidence of white matter injury and slower nerve conduction, meaning signals travel more slowly along a nerve than usual.
In the UK, a normal vitamin B12 level is generally between 201 and 914 ng/L. However, levels within the normal range can still cause symptoms.
Normal vitamin B12 levels in the United States also range from 200 to 900 ng/L, but researchers stateside are now calling for a reconsideration of nutritional guidelines.
Researchers are calling for a reconsideration of nutritional guidelines
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Vitamin B12 is an essential nutrient in animal products, nutritional yeast, fortified foods, and certain dry fruits.
The evidence for vitamin B12 preventing dementia is not clear, but scientists understand it plays a crucial role in preventing neurological dysfunction and blood cell abnormalities.
In both the UK and the US, a vitamin B12 deficiency is typically defined as a serum cobalamin level below 200 ng/L, according to NICE guidelines and the National Institutes of Health.
The study included 231 healthy individuals with a median age of 71 years, who underwent annual testing for neurological function, cognitive performance and magnetic resonance imaging. The median blood B12 concentration was 413 pmol/L.
In the United States, B12 deficiency is defined as blood levels below 148 pmol/L, which is three standard deviations below the population average.
Clinical features are often considered better indicators for supplementation.
Researchers found that low vitamin B12 levels were associated with neurological dysfunction. At low levels of B12, nerve impulses in the brain were conducted at a slower pace.
Lower B12 levels are also correlated with decreased spatial processing speed and higher white matter hyperintensity volumes.
Interestingly, these effects were observed despite participants having B12 levels within the currently accepted normal ranges.
Researchers noted that while B12 supplements resolve haematological symptoms like bruising and bleeding, they may not effectively reduce neurological symptoms, with neurological dysfunction persisting in certain individuals with normal B12 levels.
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Scientists stress that patients should monitor bioavailable B12 levels
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Scientists therefore argue that it is important to monitor bioavailable B12 levels and not just total B12 levels.
While the exact mechanism of injury remains unclear, it may be related to high homocysteine levels secondary to B12 deficiency.
How to get B12 in your diet
Vitamin B12 is naturally found in animal-based foods like fish, meat, poultry, eggs and dairy products.
Although it is not naturally present in plant-based foods, fortified breakfast cereals and nutritional yeasts provide a highly bioavailable source of vitamin B12.
