The nervous system needs more vitamin B12

- especially in older adults

When blood levels of vitamin B12 are at the low end of the normal range, there's no guarantee that there is enough to support DNA synthesis, red blood cell formation, and nerve tissue maintenance. The official reference values may be particularly problematic for older adults, who, according to an American study, have an increased risk of developing cognitive decline and dementia.

This new study was led by researchers from the University of California, San Francisco, USA.
The researchers found that a group of healthy elderly volunteers with vitamin B12 levels in the lower end of the normal range showed signs of neurological and cognitive impairment. The relatively low blood levels of vitamin B12 were associated with greater damage to the brain’s white matter. In other words, there was more damage to the myelinated nerve fibers responsible for the extensive communication between nerve cells and brain regions. These participants also had lower cognitive test scores compared to those with higher blood levels of vitamin B12. The study was published in Annals of Neurology, and according to the authors, the findings suggest a need to revisit what we consider optimal blood levels of vitamin B12.
The study included 241 healthy participants with no signs of dementia or cognitive decline. They were recruited from a study called Brain Aging Network for Cognitive Health, and the average age was 71. The participants' average blood level of vitamin B12 was 414.8 pmol/L - well above the lower reference value of 148 pmol/L. After adjusting for potential confounders such as age, gender, education, and cardiovascular risk, the researchers examined levels of the active methylated form of vitamin B12, which gives a better indication of how well the body can utilize the vitamin.
In the cognitive tests, participants with low B12 levels showed slower reaction times, which are linked to early signs of cognitive decline. This trend worsened with age. Participants with lower B12 also responded more slowly to visual stimuli, which generally indicates impaired nerve conduction. MRI scans also showed that these individuals had more white matter lesions, which may be associated with cognitive decline, dementia, or stroke.
According to the researchers, older adults appear to be at greater risk of B12 deficiency, and the current lower limit for B12 levels may be set too low. This could have more serious consequences for the general population than previously thought. The actual need for vitamin B12 should therefore be re-evaluated. In addition, health authorities might consider recommending vitamin B12 supplements for older patients with neurological issues - even if their B12 levels fall within the normal range. More research is needed, as sufficiently high levels of active vitamin B12 help protect against cognitive decline.

Sources of vitamin B12, required activation, and relevant supplements

Vitamin B12 (cobalamin) is found only in animal-based foods such as meat, fish, eggs, and dairy products. Absorption requires adequate stomach acid and a transport protein called intrinsic factor.
Foods contain the form called hydroxycobalamin, and most supplements contain cyanocobalamin, which is more stable. These forms must be converted via methylation into methylcobalamin (the form found in the blood) and 5′-deoxyadenosylcobalamin (stored in the liver). However, aging, alcohol abuse, and liver damage can impair the body’s ability to methylate vitamin B12. Acid-suppressing medications, methotrexate (used for rheumatoid arthritis), and metformin (used for type 2 diabetes) also impair the absorption or utilization of vitamin B12.
Poor ability to absorb or methylate vitamin B12 automatically increases the need for it. Vitamin B12 supplements are also available as lozenges containing methylcobalamin, which offer high absorption via the oral mucosa.

• A vitamin B12 deficiency can cause neurological damage and anemia
• Neurological damage may occur even without anemia
• Such neurological conditions are often underdiagnosed, leading to misdiagnosis and mistreatment, potentially resulting in irreversible harm
• Older adults and other vulnerable groups often have increased needs.

References

Alexandra Beaudry-Richard 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. `Healthy` vitamin B12 levels not enough to ward off neuro decline. ScienceDaily 2025

Heather Yoshimura Ang-pc. The Role of B Vitamins in Methylation Process: Clinical Applications. RUPA HEALTH 2024