Severe vitamin B12 deficiency can cause false beliefs about bug infestations in older adults, particularly those with memory problems. According to Gram Research analysis, a case report documented an 80-year-old man whose delusion began with visual illusions—misinterpreting lint and skin debris as mites—and completely resolved after vitamin B12 supplementation and brief antipsychotic treatment. Brain imaging showed reduced blood flow that improved with B12 therapy, suggesting the deficiency directly caused the psychiatric symptoms.
A case report describes an 80-year-old man who developed a strong belief that mites were infesting his body, even though no infestation existed. According to Gram Research analysis, the delusion started when he misinterpreted everyday items like lint and skin flakes as bugs—a condition called visual illusions. Doctors discovered he had severe vitamin B12 deficiency and mild memory problems. When treated with vitamin B12 supplements and a low-dose antipsychotic medication, his false beliefs disappeared within weeks. His wife, who had started believing the same thing, also recovered once he improved. This case shows that vitamin deficiencies can cause serious mental symptoms in older adults, especially those with thinking difficulties.
Key Statistics
A 2026 case report published in BMC Psychiatry documented an 80-year-old man with severe vitamin B12 deficiency who developed delusional parasitosis (false belief of mite infestation) preceded by visual illusions, with complete symptom resolution following vitamin B12 supplementation.
Brain imaging in the case showed hypoperfusion (reduced blood flow) in the medial occipital and parietal association cortices, areas responsible for vision and spatial processing, which improved following vitamin B12 treatment.
The patient’s wife, who had gradually adopted the same delusional beliefs, experienced complete resolution of her false beliefs without psychiatric medication once her husband’s symptoms improved and they spent less time together.
The Quick Take
- What they studied: How vitamin B12 deficiency might cause someone to develop a false, unshakeable belief that bugs are infesting their body and home
- Who participated: One 80-year-old man with severe vitamin B12 deficiency, mild memory problems, and his wife who temporarily shared his false beliefs
- Key finding: The patient’s delusion started with visual illusions (misreading lint and skin debris as mites), and completely resolved after treatment with vitamin B12 supplements and a low-dose antipsychotic medication
- What it means for you: If an older adult suddenly develops an intense belief about bug infestations that doesn’t make sense, doctors should check their vitamin B12 levels before assuming it’s purely a mental health problem. This is especially important for people with memory issues. Treating the vitamin deficiency may solve the problem without long-term psychiatric medication.
The Research Details
This is a case report, which means doctors documented one patient’s medical journey in detail. The 80-year-old man came to the hospital believing mites infested his body and home. Doctors performed blood tests, brain imaging, and cognitive (thinking) assessments to understand what was happening. They discovered severe vitamin B12 deficiency and areas of reduced blood flow in his brain. The team treated him with vitamin B12 injections (mecobalamin) and a small dose of an antipsychotic medication called quetiapine.
Case reports are like detailed medical stories. They’re useful for identifying new patterns or unusual presentations of known conditions, but they only describe one person’s experience. They cannot prove that something works for everyone, but they can alert doctors to look for similar patterns in other patients.
This case matters because it shows a possible chain of events: vitamin B12 deficiency → brain changes → visual illusions (misinterpreting real things) → false beliefs about bug infestations. Understanding this chain helps doctors recognize that some psychiatric symptoms in older adults may have treatable physical causes. Many older people are at risk for B12 deficiency due to medication use or absorption problems, so this connection could affect many patients.
As a case report of a single patient, this study cannot prove cause-and-effect relationships or show how common this pattern is. However, the case is well-documented with blood tests, brain imaging, and cognitive assessments. The fact that symptoms resolved when B12 was treated, and that brain imaging improved afterward, strengthens the connection between the deficiency and the symptoms. The main limitation is that we cannot know if this would happen the same way in other patients.
What the Results Show
The patient initially experienced visual illusions—he misinterpreted harmless things like lint, dust, and skin debris as mites crawling on his body and in his home. Over time, these misperceptions developed into a fixed, unshakeable belief that he was infested with mites, despite no medical evidence of infestation. Brain imaging showed reduced blood flow in areas responsible for vision and spatial awareness. Blood tests revealed severe vitamin B12 deficiency.
When doctors treated him with vitamin B12 supplements (mecobalamin) and a low dose of quetiapine (an antipsychotic), his visual illusions disappeared rapidly. Once the visual illusions stopped, his false beliefs about the mite infestation also went away. Remarkably, doctors were able to stop the quetiapine medication without the delusions returning. Follow-up brain imaging showed that blood flow to his brain had improved.
An unexpected finding was that the patient’s wife had gradually come to share his delusional beliefs—a phenomenon called folie à deux (shared psychotic disorder). Once the husband’s symptoms resolved and they spent less time together, the wife’s false beliefs also disappeared without requiring psychiatric treatment.
The patient had mild cognitive impairment (memory and thinking problems), which may have made him more vulnerable to developing false beliefs when he experienced visual illusions. The brain imaging findings of reduced blood flow in the occipital and parietal regions (areas involved in vision and spatial processing) correlated with both the visual illusions and the delusion formation. The wife’s shared beliefs resolved simply through separation and observation of her husband’s recovery, without needing medication or psychiatric intervention.
Delusional parasitosis (false belief of bug infestation) is a recognized psychiatric condition, but it’s usually treated as a primary mental health disorder. This case adds to growing evidence that metabolic problems like vitamin B12 deficiency can trigger or contribute to delusional symptoms, particularly in older adults. Previous research has linked B12 deficiency to neurological problems and cognitive decline, but this case specifically demonstrates the pathway from visual illusions to delusions. The finding that the delusion resolved with B12 treatment alone (after stopping the antipsychotic) suggests that treating the underlying deficiency may be more important than previously recognized.
This is a single case, so we cannot know how often this pattern occurs or whether it would happen the same way in other patients. We don’t know the patient’s full medical history, medications, or other factors that might have contributed. The case doesn’t tell us whether all patients with B12 deficiency and visual illusions will develop delusions, or what percentage might. We also cannot determine whether the quetiapine, the B12 treatment, or the combination was most important for recovery. Finally, this case involved an older adult with cognitive impairment—the findings may not apply to younger people or those with normal cognition.
The Bottom Line
Healthcare providers should check vitamin B12 levels in older adults who develop sudden beliefs about bug infestations, especially if they also have memory problems or other signs of cognitive decline. B12 supplementation should be considered as a primary treatment, not just an add-on to psychiatric medications. Family members who share delusional beliefs may recover without psychiatric treatment once the primary patient improves. Confidence level: Low to moderate, based on a single case, but the finding is important enough to guide clinical evaluation.
Older adults (especially those over 65), people taking certain medications that affect B12 absorption (like metformin for diabetes), vegetarians and vegans, and people with digestive disorders should be aware of B12 deficiency risks. Family members of people developing unusual beliefs about infestation should encourage medical evaluation. Healthcare providers should consider this case when evaluating delusional parasitosis in older patients. People with mild cognitive impairment may be at higher risk. This case is less relevant to younger adults with normal cognition unless they have known B12 deficiency or absorption problems.
In this case, visual illusions improved within days to weeks of starting B12 treatment, and the delusional beliefs resolved shortly after. However, this timeline may vary from patient to patient. Full recovery of brain blood flow took several weeks. Realistic expectations would be to see improvement in visual symptoms within 2-4 weeks of starting B12 treatment, with resolution of false beliefs following within 4-8 weeks if B12 deficiency was the primary cause.
Frequently Asked Questions
Can vitamin B12 deficiency cause delusions or false beliefs?
Yes, according to a 2026 case report, severe B12 deficiency can trigger delusional beliefs, particularly in older adults with cognitive impairment. The deficiency caused visual illusions that progressed to false beliefs about bug infestation, which resolved with B12 treatment.
What are the early signs of B12 deficiency affecting the brain?
Early signs include visual illusions (misinterpreting objects), memory problems, confusion, and unusual perceptions. In this case, the patient misread lint and skin debris as mites before developing the full delusion. Older adults should seek evaluation if experiencing these symptoms.
Can someone else catch delusional beliefs from a family member?
Yes, a phenomenon called folie à deux (shared psychotic disorder) can occur. In this case, the patient’s wife gradually adopted his false beliefs about mite infestation. Her beliefs resolved without medication once her husband recovered and they separated more.
Who is at highest risk for B12 deficiency?
Older adults (over 65), vegetarians and vegans, people taking metformin or certain stomach medications, and those with digestive disorders are at highest risk. Regular B12 screening is recommended for these groups to prevent neurological complications.
How quickly does B12 treatment improve psychiatric symptoms?
In this case, visual illusions improved within days to weeks of starting B12 supplementation, with delusional beliefs resolving within weeks. However, individual timelines vary. Full brain imaging improvements took several weeks.
Want to Apply This Research?
- Users could track B12 levels (if they have deficiency) through lab results logged in the app, noting dates of supplementation and any changes in perception (visual clarity, misinterpretations of objects, or unusual beliefs). This creates a record to share with healthcare providers.
- For users at risk of B12 deficiency (older adults, vegetarians, those on certain medications), the app could send reminders to schedule annual B12 level checks and track dietary B12 sources or supplementation compliance. Users could log any visual changes or unusual perceptions to discuss with their doctor.
- Long-term tracking could include quarterly B12 level checks, cognitive function self-assessments, and a simple visual perception log (noting any misinterpretations of objects). Users could also track mood and belief patterns to identify any changes that might warrant medical evaluation. This data helps both users and healthcare providers monitor treatment effectiveness.
This case report describes one patient’s experience and cannot be generalized to all people with similar symptoms. Delusional beliefs and visual illusions have many possible causes and require professional medical evaluation. Do not self-diagnose or self-treat based on this information. If you or a loved one experiences persistent false beliefs, visual disturbances, or unusual perceptions, consult a healthcare provider immediately for proper evaluation and diagnosis. Vitamin B12 supplementation should only be undertaken under medical supervision, as excessive B12 can have side effects in some individuals. This information is educational and not a substitute for professional medical advice, diagnosis, or treatment.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.