Brain health is at risk due to vitamin B12 recommendations that are too low

Vitamin B12 is crucial for the nervous system and the formation of blood cells. However, the official recommendations (RI) are apparently set too low when it comes to protecting the aging brain. This is shown by an American population study, published in the Annals of Neurology, in which researchers found that older adults with "normal" but lower levels of vitamin B12 show signs of slower thinking and delayed responses to visual impressions.

Vitamin B12 is best known for its role in the formation of red blood cells, DNA, and a healthy nervous system. This means that vitamin B12 is crucial for energy levels and cognitive abilities. In addition, vitamin B12 is important for fat metabolism and for the breakdown of the amino acid homocysteine, which acts as a toxin when present in excessive amounts.
Although the relationship between vitamin B12 deficiency and dysfunctions in the brain is well documented, not enough has been known about the optimal amounts when it comes to cognitive functions and protection against localized neurological damage. The purpose of the new American study was therefore to examine this relationship more closely among older people.
The study was conducted at the University of California, San Francisco, and included 231 healthy older volunteers with an average age of 71 years. The participants' average blood vitamin B12 level was measured at 414.8 pmol/L, which should be considered acceptable since the lower reference value in the United States is 148 pmol/L. The participants were also subjected to various tests of, among other things, their visual and cognitive responsiveness, as well as MRI scans to assess their neurological status.
In addition, the researchers measured various biomarkers associated with damage to the nervous system. More specifically, the biomarkers concerned damage to the axons of nerve cells, which are the cholesterol-containing "wires" that nerve cells use for communication and which make up the brain's white matter. The researchers also measured damage to astrocytes, which are support cells (glial cells) in the central nervous system.
Furthermore, the researchers measured accumulations of harmful proteins called amyloids, which can cause the pathological changes seen in dementia and Alzheimer's disease and which increase the risk of stroke.

More cognitive and neurological problems

The study showed that a low level of active vitamin B12 (holo-transcobalamin) was associated with a slower visual and cognitive response. This can have serious consequences and interfere with everything from driving a car to other everyday activities.
In addition, a low vitamin B12 level was associated with more pathological changes in the brain's white matter, indicating poorer connections between nerve cells and an increased risk of cognitive decline, dementia, and stroke.
Overall, the researchers found that healthy older individuals who had vitamin B12 values within the normal range but in the lower end of that range showed signs of more cognitive and neurological problems. This means that even though these older individuals may be told that their vitamin B12 level is fine, a genuine deficiency may still be present, causing damage to the central nervous system. Moreover, these changes appear to worsen with age.

Why are older adults more vulnerable?

Vitamin B12 is found only in animal-based foods, and absorption from the small intestine requires a carrier protein called intrinsic factor.
The researchers behind the study focused on older participants because the aging process itself can impair the absorption and utilization of vitamin B12. In addition, certain gastrointestinal disorders as well as various medications such as metformin, methotrexate, and acid-reducing medications can impair the absorption or utilization of vitamin B12. It is also problematic if older adults eat very little or consume a plant-based diet without vitamin B12.

More focus on adequate vitamin B12 and supplementation for older adults

According to the researchers behind the study, the vitamin B12 requirements of older adults should be redefined, and in practice health authorities should also consider recommending supplements if older individuals have vitamin B12 levels in the lower end of the normal range. In this way, providing more vitamin B12 to older adults may help prevent cognitive decline, dementia, and related diseases.
It may be advantageous to choose vitamin B12 supplements in the form of lozenges, since vitamin B12 is more easily absorbed directly into the bloodstream through the mucous membrane of the mouth.

References:

Alexandra et al. Vitamin B12 Levels Association with Functional and Structural Biomarkers of Central Nervous System Injury in Older Adults. Annals of Neurology. 2025

University of California – San Francisco. Scientists warn that current vitamin B12 guidelines may be putting your brain at risk. ScienceDaily 2026