In the world of integrative medicine and functional psychiatry, we talk a lot about the importance of nutrition and micronutrient status for mental health. Yet, one of the most overlooked and underdiagnosed deficiencies—one that can have a profound impact on mood, cognition, and overall well-being—is vitamin B12.
The Problem with Current B12 Testing
Most clinicians rely on standard serum B12 tests to assess levels, but this method is deeply flawed. A so-called “normal” B12 level—typically defined as above 200 pg/mL in the U.S.—does not necessarily mean optimal. In fact, neurological symptoms can begin even in the lower end of the normal range.
A recent study found that older adults with B12 levels in this low-normal range were more likely to experience cognitive and neurological symptoms, as well as structural brain changes consistent with neurodegeneration (Beaudry-Richard et al., 2025). The researchers concluded, “These findings suggest that current parameters for defining adequate B12 levels may be inappropriate when considering neurophysiological, neuropsychological, serological, and neuroradiological outcomes.”
Even worse, serum B12 doesn’t tell us how well the body is utilizing the vitamin at the cellular level. Functional markers such as methylmalonic acid (MMA) and homocysteine provide a much clearer picture. Holotranscobalamin (holoTC), though less accessible in the U.S., is another important marker for B12 status and absorption.
How Many People Are Affected? More Than You Think…
B12 deficiency is often associated with vegan or vegetarian diets, but many omnivores also suffer from low levels. Absorption issues are common, particularly in:
- Older adults
- People with gut conditions (IBS, IBD, celiac, low stomach acid)
- Individuals on acid-blocking meds (like PPIs)
- People exposed to certain chemicals, like nitrous oxide
- Patients with methylation issues (e.g., MTHFR mutations)
This isn’t just a minor nutritional gap. B12 is essential for red blood cell formation, nerve function, and DNA synthesis. Without it, both the body and the brain suffer.
The Mental Health Connection
Vitamin B12 plays a critical role in mental and emotional health. Deficiency has been linked to:
- Depression – Often correlates with low B12 (Fatima et al., 2023)
- Cognitive Decline – Associated with memory issues, brain fog, and even early dementia (Jatoi et al., 2020)
- Fatigue & Low Motivation – Neurological symptoms can present as persistent fatigue (Pfnür, 2022)
- Psychosis & Paranoia – Severe deficiencies may cause psychiatric symptoms (Sahu et al., 2022)
Because these symptoms mimic many psychiatric conditions, B12 deficiency is frequently misdiagnosed. Instead of addressing the root cause, patients may be placed on psychiatric medications, which do not correct the underlying issue.
What Can We Do?
- Rethink Testing – Don’t rely on serum B12 alone. Consider MMA, homocysteine, and intrinsic factor antibodies for a more complete assessment.
- Look Beyond Diet – Absorption matters. Patients on certain medications or with gut issues may need B12 even if their diet includes animal products.
- Use the Right Form – Methylcobalamin, adenosylcobalamin, and hydroxycobalamin are most bioavailable. Avoid over-relying on cyanocobalamin.
- Consider Injections – For those with severe deficiencies or poor absorption, intramuscular B12 injections can be transformative.
The Bottom Line
Vitamin B12 deficiency is a silent but significant contributor to mental health struggles and cognitive decline. Given the limitations of conventional testing, a more thorough and functional approach to assessment is crucial. With the right form and delivery method of B12, many patients can experience meaningful improvements in energy, mood, and cognitive clarity.
This is one small but powerful example of how integrative psychiatry can change lives—by finding and treating the root cause.
Sources available upon request. For more information or to schedule a micronutrient evaluation, contact Mindset & Body Reset today.
