Scientists warn current vitamin B12 guidelines may be putting brains at risk
A joint study by the University of California Davis and the University of California San Francisco (UCSF) has suggested that current vitamin B12 threshold values should be re-evaluated in the relationship between cognitive decline and brain white-matter changes in older adults. The study's findings were published last week in the journal Annals of Neurology.
The study included 231 healthy older adults (mean age 71.8 years) as participants. All had B12 levels within the laboratory-defined 'normal' range; nevertheless, the researchers found that lower (though still within-normal) levels were associated with lower cognitive-test scores and more brain white-matter lesions on magnetic resonance imaging (MRI).
The study's lead author, Dr Ari Green from the UC Davis Health System Department of Neurology, said in a press statement that 'current authoritative guidelines may be insufficient; the optimal threshold for B12 levels, particularly in older adults, should be defined considerably above what is currently accepted'. Green said the study should restart the global conversation about lifetime B12 thresholds.
The researchers determined that participants in the lowest B12 quartile (between 134 and 209 pmol/L) performed 0.4 standard deviations below those in the highest quartile (above 300 pmol/L) on cognitive testing. MRI scans showed brain white-matter lesions (particularly in subcortical areas) were markedly more prevalent in this group.
An important nuance: the study participants were not people clinically diagnosed with B12 deficiency. The European Food Safety Authority (EFSA) and the United States National Academy of Medicine accept the current lower bound of 148 pmol/L; however, the study suggests that, for cognitive health preservation, the threshold should be above 200 pmol/L.
Mechanistically, vitamin B12 is a critical cofactor in the production of the myelin sheath, which plays a key role in nerve signal transmission. Low B12 reduces myelin production, and this provides the underlying biological explanation for the MRI findings in the study. Dr Joel Kramer from UCSF, who participated in the research, told Science Daily that 'the neurological effects of B12 are already a known phenomenon; this study provides clear evidence for why the thresholds need to be redrawn'.
What is the practical meaning for the general population? Less than half of the participants in the study (41 per cent) were taking known B12 supplements; nevertheless, even among those who supplemented, 38 per cent did not reach the 300+ pmol/L level considered optimal. B12 absorption efficiency in older adults declines with age, so individuals who are not vegan or vegetarian may also be at risk.
Independent commentator on the study, nutrition expert Dr Edith Heys of Tufts University, told BBC Health Online that 'this study marks a turning point for dietitians; when we evaluate our patients holistically, interpreting B12 levels by temporary 'normal' bounds is not the right approach'. Heys noted that supplementation can be applied with no side-effect risks such as hair loss.
A caveat that clinical translation may be slow was issued by Dr Maria Hubbard, spokesperson for the EFSA Nutrition Panel: 'a threshold revision is not made on a single study; guidelines do not change until the same findings are confirmed by multiple independent cohorts'. Hubbard said a new EFSA evaluation is planned for early 2027.
B12 levels need to be evaluated individually. This article is a science news commentary and not medical advice; if you have concerns about B12 levels, it is recommended to discuss a simple blood test with your physician. Supplementation doses are determined by considering factors such as kidney function and existing medication therapies.