Are We Getting Enough Vitamin B12?

By Wayne Persky

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According to recent research, most MC patients probably need more B12 than we realize. B12 is absorbed in the stomach, implying that anyone with compromised digestion is at increased risk of developing a B12 deficiency. And digestion is certainly compromised when MC or any other IBD is active.

Interestingly, a B12 deficiency can cause many of the same symptoms as MC.

​A B12 deficiency can cause gastrointestinal symptoms such as bloating, constipation, diarrhea, gas, and nausea, for example. Is it possible that some of the cases where MC seems to be refractive to dietary treatment, despite careful attention to a restricted diet, might be associated with a B12 deficiency? That certainly appears to be a possibility.

​B12 deficiency seems to be associated with many autoimmune diseases.

For example, B12 deficiency is common among diabetes patients (Kibirige, and Mwebaze, 2013).1 Published research has clearly shown that not only is neuropathy common among diabetics, but for patients who have diabetic neuropathy, the degree of neuropathy is inversely proportional to the level of B12 in their blood. In other words, diabetes patients who have the most serious levels of neuropathy. also have the lowest plasma levels of B12.

New research questions the adequacy of adult B12 RDA.

The possibilities discussed in the previous paragraphs gain substance in view of recent research led by scientists at the University of California, San Francisco (UCSF), 2025, February 19.2 The findings of the study challenge the long-held belief that maintaining vitamin B12 levels within the currently accepted "normal" range is sufficient to prevent neurological decline, particularly in older adults. Published in the Annals of Neurology, the study found that even individuals with B12 levels considered healthy by existing standards may be at risk for cognitive impairment and brain damage (Beaudry-Richard, et al., 2025).3

​The study involved 231 healthy older adults with an average age of 71 years. Participants had an average blood B12 level of 414.8 pmol/L, well above the U.S. minimum standard of 148 pmol/L. Despite being within the normal range, individuals with lower B12 levels showed signs of neurological impairment and cognitive decline.

Brain scans revealed the neurological effects of low "normal" B12 levels.

MRI scans revealed increased white matter damage in participants with lower B12 levels. White matter lesions are associated with cognitive decline, stroke risk, and dementia. Participants with lower active B12 levels had slower reaction times and impaired visual processing speeds.​

Older participants were especially vulnerable, with age amplifying the negative effects of low B12. Elevated levels of Tau protein (a marker associated with neurodegenerative diseases like Alzheimer’s disease), were linked to high levels of biologically inactive B12 fractions (holo-haptocorrin).

Vitamin B12 plays a vital role in:

• DNA synthesis and red blood cell production.
  
• ​Fatty acid and amino acid metabolism, which are critical for maintaining the myelin sheath that surrounds and protects nerve fibers.
• Supporting the production of neurotransmitters essential for cognitive functions like memory, focus, and processing speed.

A deficiency (even within the so-called normal range) may lead to brain damage through:

• ​Demyelination (damage to the myelin sheaths) of nerve fibers, impairing electrical signal conduction in the brain.
• Reduced synthesis of neurotransmitters, slowing down cognitive processing

Notice that this research was based on measurements of active B12.

B12 in food and cheap vitamins is in the inactive form (cyanocobalamin), which must be converted (by a methylation process) to the active form before our body can use it. About half the general population has one or more methylenetetrahydrofolate reductase (MTHFR) gene mutations which can limit our ability to convert vitamins into the active form. Some of us have major MTHFR gene mutations, which prevents our body from being able to use normal amounts of the B12 in our food, or most common vitamins. In such cases, a blood test may show our B12 level to be normal, or above the normal range, yet our body is screaming for the active form of B12.​

This deficiency can be resolved either by receiving regular B12 injections at our doctors office, or by taking an active form (methylcobalamin, for example) of B12. And according to the study cited above, our ability to absorb and/or convert B12 into the active form decreases as we age.

MC depletes water-soluble vitamins.

And since MC (and the other IBDs) deplete water-soluble vitamins, our chances of developing a B12 deficiency are much higher than someone who doesn't have a gastrointestinal disease that causes diarrhea. Considering our disease symptoms, and our general age bracket, it appears quite likely that B12 deficiency is common among MC patients.

Long-term brain fog and fatigue are common symptoms of MC.

Could a high prevalence of B12 deficiency be responsible for the brain fog and long-term fatigue associated with MC?

​Since the risk of deficiency increases with age, maintaining adequate vitamin B12 levels is particularly important for older adults. The decline is mostly due to a natural decline in the stomach’s ability to produce intrinsic factor (a protein required for B12 absorption from food).

Disease-related malabsorption exacerbates the problem.

For adults over 50, not only age-related changes, but diseases such as MC and other IBDs, lead to malabsorption of B12 from dietary sources. Low stomach acid (atrophic gastritis) or the use of medications such as proton pump inhibitors (PPIs) or metformin, can further reduce B12 absorption. As mentioned above, a deficiency in this vitamin can lead to serious health issues, including:
​

• Anemia
• Cognitive decline and memory loss
• ​Peripheral neuropathy (tingling and numbness in the hands and feet)

Fortunately, supplementation can help address this problem effectively.

Instead of basing our B12 intake on the government's RDA guidelines,

it appears that following the recommendations of the Linus Pauling Institute (LPI) may be more appropriate, especially for individuals such as us, who have MC, or some other IBD.

Their recommendations state that adults over 50 should take 100–400 μg (micrograms) of supplemental vitamin B12 daily. These doses help overcome the body's natural decline in absorption by providing much higher amounts than would be possible through food alone.

The good news is that most multivitamins already meet or exceed these recommendations, making it easy for most seniors to get the right amount through daily supplementation. The bad news is that a major caveat regarding multivitamins exists for MC patients, due to the fact that multivitamins tend to contain so many ingredients that most such products on the market pose a significant reaction risk for MC patients​

There are several forms of vitamin B12 available in supplements,  

although not all are equally effective for everyone:​

• Cyanocobalamin is the most common and affordable form, and it's effective for most people. However, it may not be ideal for those who have methylation issues, or kidney disease. For those who have kidney disease, there are concerns about cyanide accumulation in impaired kidneys.
• Methylcobalamin is a naturally occurring, bioactive form that's much better suited for people who have kidney issues or genetic methylation defects.
• Hydroxycobalamin is often used in injections, particularly for treating severe deficiencies or specific medical conditions.​

These forms of B12 are available as:

• Oral supplementation in the form of tablets or capsules is usually effective even in cases of poor absorption due to the high available doses.
• Sublingual tablets or sprays are absorbed directly into the bloodstream through tissues under the tongue, and are useful for those who have severe or absorption issues.
• Intramuscular injections that are administered by healthcare providers for individuals who have severe deficiency, or conditions such as pernicious anemia can resolve even the most severe cases of B12 deficiency.
• B12 can also be found in fortified cereals, nutritional yeast, and plant-based milks. And such foods can complement supplementation, although they are generally insufficient for seniors when used without additional supplementation.

Does a risk of overdose exist?

No toxic effects have been associated with high vitamin B12 intake in healthy individuals, even at doses as high as 2,000 μg/day. This is because the body absorbs only a small fraction of large doses, with the rest excreted in urine. However, as is the case when taking supplemental magnesium, those who have compromised kidney function should consult their healthcare provider before starting high-dose cyanocobalamin (methylcobalamin bypasses this risk).

In summary:

For seniors, and especially those who have MC or some other IBD, the easiest and most effective way to maintain adequate B12 levels is:

• A daily oral supplement containing 100–400 μg of vitamin B12, ideally in the form of methylcobalamin for those who have methylation issues or compromised kidney function.
• Regular blood tests to monitor B12 levels, especially if there are signs of deficiency.

This approach ensures that we can maintain healthy B12 levels, supporting brain function, nerve health, and energy metabolism well into our senior years.

References:

1. Kibirige, D., and Mwebaze, R. (2013). Vitamin B12 deficiency among patients with diabetes mellitus: is routine screening and supplementation justified? Journal of Diabetes & Metabolic Disorders, 12(1), p17. Retrieved from https://pmc.ncbi.nlm.nih.gov/articles/PMC3649932/

2. University of California, San Francisco, (2025, February 19). 'Healthy' vitamin B12 levels not enough to ward off neuro decline: Experts call for new recommendations for older adults. Medical Xpress, Retrieved from https://medicalxpress.com/news/2025-02-healthy-vitamin-b12-ward-neuro.html

3. Beaudry-Richard, A., Abdelhak, A., Saloner, R., Sacco, S., Montes, S. C., Oertelm F. C., . . . Green, A. J. (2025). Vitamin B12 Levels Association with Functional and Structural Biomarkers of Central Nervous System Injury in Older Adults. Annals of Neurology, Retrieved from https://onlinelibrary.wiley.com/doi/10.1002/ana.27200