- Vitamin B12 is needed for the development and function of nerve tissue and the brain, and for the formation of red blood cells and DNA.
- It is found in protein foods such as fish, meat, eggs and dairy, as well as fortified breakfast cereals and nutritional yeast, and can be taken as a supplement.
- Vitamin B12 deficiency is rare, but low or marginal levels are common, affecting up to 40% of Western populations.
- A new study has found that, in older people, both lower and higher levels of vitamin B12 may be associated with cognitive issues, even when these levels are within the normal range.
Vitamin B12, also known as cobalamin, is a water-soluble vitamin that is essential for developing and maintaining a healthy central nervous system, red blood cells and
The National Institutes of Health (NIH) recommend that people over the age of 14 should get 2.4 micrograms of B12 per day, and that dairy products, fish, meat, poultry, and eggs are
However, a new study in healthy older adults has found that, even within the normal range of vitamin B12, lower and higher levels may have effects on cognition.
The study, which is published in
“This study […] noted elderly patients with low B12 levels had slowing of an electrical impulse from their eye to their occipital lobe and proposed this could be due to B12 affecting the insulation of brain nerves. […] It concluded rethinking what a low B12 level should be in clinical practice. [This] is very reasonable as I routinely treat patients with B12 levels that are technically within normal though have memory loss.”
— Clifford Segil, DO, neurologist at Providence Saint John’s Health Center in Santa Monica, CA, not involved in the study.
The older adults in the study were all recruited for the Brain Aging Network for Cognitive Health at the University of California San Francisco.
From all the adults in the study, researchers enrolled 231 healthy older volunteers (mean age 71.2 years). These participants gave blood samples for measurement of serum total B12 and levels of holo-transcobalamin (holo-TC), or ‘active B12’ — the B12 that is biologically available to cells.
All but 2 of the participants, whose B12 was deficient, had levels within the normal range.
For analysis, the researchers divided the participants into those with B12 levels below and above the mean of 408pmol/L. They also corrected for age, sex at birth, cardiovascular risk factors,
They found that B12 levels below the mean were significantly associated with a delay in
People with lower B12 levels also had slower processing speeds, an effect that the researchers found increased with age, and larger volumes of white matter hyperintensities, brain changes that are associated with cognitive impairment.
Ari J. Green, MD, Chief of the Division of Neuroimmunology and Glial Biology, UCSF, and lead author on the study, told Medical News Today:
“Our work shows what appear to be multiple negative effects for some people when their B12 levels are in the lower range of what has long been considered adequate or normal (and would not qualify as deficient). This includes slowed transmission of signals in the brain, slowed processing speed on cognitive tests and MRI evidence of white matter injury. Most importantly, these effects are strongest when looking at the ‘active’ fraction of B12 (which is not routinely checked) rather than just total blood B12 levels.”
At the other end of the scale, the researchers found that higher levels of B12 also had effects that may impact cognition.
Those people with higher B12 levels had increased levels of T-Tau protein, which is associated with neurodegeneration and dementia. This association was strongest when there were low levels of active B12 and high levels of holo-HC, or ‘inactive B12’.
Segil suggested that further research was needed to verify why the study might have found this. Green concurred:
“We also saw that high levels of ‘inactive’ B12 in the blood may be associated with a blood marker of axon injury. It should be noted that we did not have a means of directly measuring inactive B12 levels in the paper but had to calculate the level from other measurements. The full meaning of this result needs further study but it suggests that measuring total blood B12 may mislead doctors and patients in some situations to think that active B12 levels are adequate.”
“We believe that recommendations for B12 should be very likely be reconsidered — and not just based on B12 blood levels but considering measures of active vs inactive B12 and looking at measures of neurological and cognitive function. Measuring what is adequate by just measuring what is average (and the distribution) in the population does not prove that the levels are adequate for any nutrients,” Green told us.
The authors suggest that the observed detrimental effect of low B12 on cognitive processes may be caused by changes in the integrity of the myelin surrounding nerve cells. However, they emphasise that their study did not look into how these changes might occur.
However, they suggest that elderly people may be particularly vulnerable to declining levels of B12, so the guidelines for healthy B12 levels may need to be revised for this population.
“There is lots of additional research that needs to be done. The reasons why inadequate B12 causes neurological dysfunction— specifically which cell types in the brain and which parts of the nervous system most require B12 — is completely unclear. This needs careful scientific and laboratory work which is currently going on in our laboratory and affiliated labs.”
— Ari J. Green, MD, lead author of the study
To ensure adequate B12, people should include foods that are rich in the vitamin in their diet. Segil advised that salmon and beef are two of the best sources of B12. As plant foods do not contain B12, vegetarians and vegans might benefit from supplements to ensure Healthy levels.
The
“Both kids and adults can get B12 deficiencies from absorption issues even if they eat a diet high in B12 products,” adding, “for the general public, I would recommend using a multivitamin with B12 in it rather than a B12 supplement, which can come in a liquid form, gel cap or regular tab,” Segil said.
