Which Vitamin Deficiencies Cause Psychosis?

Several vitamin deficiencies can trigger or contribute to psychotic symptoms, including hallucinations, delusions, and disordered thinking. The best-documented culprits are vitamin B12, folate (B9), niacin (B3), thiamine (B1), and vitamin D, though emerging evidence implicates vitamins B6 and C as well. What makes these deficiencies clinically treacherous is that psychiatric symptoms sometimes appear months or years before any of the physical signs doctors are trained to look for, which means the real cause can go unrecognized while patients receive psychiatric diagnoses and medications they may not need long-term.

Vitamin B12 and Psychosis

B12 deficiency is the most thoroughly studied nutritional cause of psychosis. The psychiatric picture can include auditory and visual hallucinations, paranoid delusions, disorganized thinking, agitation, and severe cognitive decline.¹ What catches many clinicians off guard is that these mental changes can show up without anemia or any of the classic blood-count abnormalities traditionally associated with B12 deficiency.² A patient may walk into a psychiatric emergency room with florid psychosis, normal-looking blood work, and no obvious reason for a doctor to order a B12 level. One case report described a patient whose presentation was so purely psychiatric that B12 deficiency was not identified until after other diagnoses had been explored.³

The psychiatric symptoms can appear months or even years before the hematological signs that textbooks describe as hallmarks of the condition.⁴ In severe cases, B12 deficiency has been linked to seizures alongside psychosis, suggesting that the neurological damage can become extensive.⁵ The mechanism involves B12’s role in producing myelin, the insulating sheath around nerve fibers, and in the chemical reactions that produce neurotransmitters like serotonin and dopamine. When B12 is absent, both the structural wiring and the chemical signaling of the brain deteriorate.

Folate and First-Episode Psychosis

Folate, also called vitamin B9, works hand-in-hand with B12 in the same biochemical pathway. Low folate levels show up with striking frequency in people experiencing their first psychotic episode. A systematic review and meta-analysis found that people with first-episode psychosis had markedly lower blood levels of folate compared to healthy individuals, and that lower folate predicted more severe negative and general psychiatric symptoms.⁶ A separate study of 188 young patients with psychosis found that about a third had an abnormality in the metabolic pathway that folate supports, with folate deficiency itself present in roughly one in five patients and closer to one in four among those with a first episode.⁷

In that same study, male patients had lower folate levels than female patients, and lower folate correlated with more severe illness overall. An analysis of the largest available cohort of first-episode schizophrenia-spectrum patients found that about 18% had decreased B12 or folate levels.⁸ The question of whether low folate causes psychosis or whether the early stages of psychosis lead people to eat poorly and become folate-deficient remains one of the harder puzzles in the field. The association, however, is consistent enough that most researchers agree routine screening is warranted.

The Genetic Angle on Folate

Some people are genetically predisposed to folate-related trouble. A common genetic variation in the MTHFR gene, which encodes an enzyme critical for processing folate, has been linked to an increased risk of schizophrenia. A review of genetic association studies found that people carrying two copies of certain MTHFR variants had a roughly 25% to 60% higher risk of schizophrenia compared to those without the variants.⁹ People with these variants process folate less efficiently, which means they may need higher dietary intake or supplementation to maintain the same functional levels as someone without the variant. This is a case where “normal” folate intake might not be enough for a person whose biochemistry handles it poorly.

Niacin and Pellagra

Niacin deficiency causes pellagra, a condition historically described by a grim set of symptoms: dermatitis, diarrhea, dementia, and, if untreated, death. The “dementia” in that list is a catch-all for a wide range of psychiatric symptoms that frequently includes frank psychosis. In one documented case, a patient was admitted to a psychiatric hospital for disorderly behavior and initially diagnosed with unspecified psychosis. Despite having the classic skin rash and eventually developing diarrhea, it took 20 days for clinicians to recognize that pellagra was the actual problem.¹⁰

Another case involved a patient presenting with altered mental status who developed diarrhea during the hospital stay. After extensive testing, pellagra was identified, and the patient improved with niacin supplementation.¹¹ A third case documented a young man who developed auditory hallucinations, suspiciousness, and agitated behavior on top of years of weakness and poor appetite, with the characteristic scaly skin rashes appearing on his hands, face, and neck.¹² Pellagra is considered rare in developed countries, but it still shows up in people with severe alcohol dependence, eating disorders, malabsorption conditions, and extreme dietary restriction. Niacin is essential for producing neurotransmitters, and without it, brain function breaks down in ways that can look identical to a primary psychiatric illness.

Thiamine and Wernicke-Korsakoff Syndrome

Thiamine, vitamin B1, is most famous for its role in Wernicke-Korsakoff syndrome, a condition seen almost exclusively in people with chronic heavy alcohol use or severe malnutrition. Wernicke’s encephalopathy is the acute phase, involving confusion, coordination problems, and eye movement abnormalities. If untreated, it can progress into Korsakoff syndrome, defined by severe memory and learning deficits that are out of proportion to other cognitive abilities in an otherwise alert patient.¹³

While Korsakoff syndrome is technically more of a memory disorder than a psychotic one, the confusion and confabulation (filling in memory gaps with fabricated stories that the patient genuinely believes) can look psychotic to an untrained observer. The acute Wernicke phase can also involve hallucinations and paranoia. Thiamine deficiency does not just affect people with alcohol use disorders. A meta-analysis found that roughly 27% of patients who undergo bariatric surgery develop thiamine deficiency, making lifelong supplementation necessary for this population.¹⁴ Anyone with significantly reduced food intake or absorption is at risk.

Vitamin D and Schizophrenia Risk

Vitamin D’s relationship to psychosis is different from the B vitamins discussed above. Rather than causing acute psychotic symptoms in an otherwise healthy adult, vitamin D deficiency during development appears to increase the long-term risk of schizophrenia. Two large studies based on dried blood spots from newborns in Denmark found that babies born with low vitamin D levels went on to develop schizophrenia at higher rates than those with adequate levels.¹⁵ Animal research has shown that vitamin D deficiency during brain development alters neurological and behavioral outcomes in ways that parallel schizophrenia features.¹⁶

Separately, vitamin D deficiency is common in people already experiencing first-episode psychosis. The same meta-analysis that documented low folate levels in first-episode patients also found significantly lower vitamin D levels in that group compared to controls, with an even larger effect size than folate.⁶ Whether low vitamin D in adults actively worsens psychotic symptoms or is simply a consequence of the lifestyle changes that come with psychosis (staying indoors, poor diet) remains an open question. Researchers have described the developmental link as “plausible and warranting ongoing research” while noting that vitamin D deficiency in adulthood produces subtler effects in animal models and does not reliably reproduce psychosis-like behavior.

Vitamin B6 and Vitamin C

The evidence for vitamins B6 and C is thinner but worth knowing about. In mice, vitamin B6 deficiency caused a surge in noradrenaline release in the prefrontal cortex and striatum, leading to social deficits and cognitive impairment. When researchers supplemented B6 directly into the brain or used a drug to counteract the excess noradrenaline, the behavioral problems resolved.¹⁷ This is animal research and does not directly prove that B6 deficiency causes psychosis in humans, but it does identify a plausible brain mechanism. B6 is essential for synthesizing several neurotransmitters, so severe deficiency could theoretically disrupt the chemical balance enough to produce psychiatric symptoms.

Vitamin C deficiency, better known as scurvy, has traditionally been thought of as a physical disease with bleeding gums, bruising, and fatigue. But a case series documented a patient who developed new-onset psychotic symptoms with only borderline-low vitamin C levels and no physical signs of scurvy at all. The psychotic symptoms improved significantly with vitamin C supplementation alone.¹⁸ The researchers coined the term “neuropsychiatric scurvy” to describe cases where psychiatric symptoms appear in isolation, before the classic physical signs develop. Given that vitamin C plays a role in neurotransmitter synthesis, this makes biological sense even if clinical documentation is still sparse.

Why These Deficiencies Get Missed

The core problem is one of clinical habit. When a patient arrives in an emergency department with hallucinations or paranoia, the standard workup focuses on psychiatric diagnoses. Vitamin levels are not routinely measured. Several of the case reports in the literature describe patients who were started on antipsychotic medications before anyone thought to check their nutritional status. In one case series, once vitamin B12 deficiency was identified and treated, patients were able to taper off or completely discontinue antipsychotics within one to six months.¹⁹ That outcome is dramatically different from the trajectory of someone placed on lifelong antipsychotic therapy for a primary psychiatric disorder.

The difficulty is compounded by the fact that vitamin deficiencies can cause psychiatric symptoms before they cause anything else. A person can have psychosis from B12 deficiency without anemia, without nerve tingling, without a single physical clue.⁴ The same is true of niacin-related psychosis before the skin rash appears, and of vitamin C-related psychosis before bleeding symptoms emerge. If a clinician waits for the “typical” physical signs before ordering a vitamin panel, the window for early correction has already passed.

Who Is Most at Risk

Certain groups are disproportionately vulnerable to developing vitamin deficiencies severe enough to affect the brain:

Older adults: Absorption of B12 declines with age, and medications commonly prescribed to older patients, especially proton pump inhibitors and metformin, further reduce B12 levels in a dose- and duration-dependent pattern.²⁰
People who have had bariatric surgery: The altered gut anatomy reduces absorption of thiamine, B12, folate, and fat-soluble vitamins like vitamin D.
Strict vegans: B12 is found almost exclusively in animal products. Without supplementation, deficiency is inevitable over time.
People with alcohol use disorders: Alcohol impairs absorption of thiamine, folate, and niacin, while also increasing the body’s demand for these vitamins.
People with eating disorders or very restricted diets: Any severe dietary limitation raises the risk of multiple concurrent deficiencies.
People with autoimmune conditions: Pernicious anemia, an autoimmune destruction of the cells that help absorb B12, is a well-known cause of severe deficiency.

Does Supplementation Help Once Psychosis Has Developed

The answer depends heavily on which vitamin is missing and how early it is caught. For B12 deficiency, the evidence is encouraging. In one case series, all patients with B12-deficiency psychosis improved significantly with a combination of low-dose antipsychotics and B12 replacement, and most were able to reduce or stop antipsychotic medication entirely within a year of follow-up, with regular B12 monitoring ensuring they remained well.¹⁹ Similarly, the pellagra cases resolved once niacin was provided, and the vitamin C psychosis case improved with supplementation.

The picture is less clear-cut for people who already have an established psychotic disorder like schizophrenia and happen to also have low vitamin levels. A double-blind trial giving B-vitamin supplements (B12, B6, and folic acid) to people with first-episode psychosis found no significant improvement in symptoms or cognitive function compared to placebo.²¹ There is a critical difference between psychosis caused by a deficiency and a primary psychiatric illness that happens to coexist with a deficiency. In the first scenario, correcting the deficiency treats the root cause. In the second, the vitamins are treating a bystander, not a driver.

Vitamin D supplementation showed more promise in one randomized trial of patients with schizophrenia, where the supplementation group had a significant reduction in overall symptom severity compared to placebo.²² A review concluded that there is growing evidence that supplementation with folate, B12, and vitamin D may be important for certain subgroups of patients with schizophrenia, even if it does not help everyone across the board.²³ The challenge is identifying which patients will benefit, a task that routine blood testing could at least begin to address.

Medications That Quietly Deplete Vitamins

One underappreciated pathway to deficiency-related psychiatric symptoms runs through the medicine cabinet. Proton pump inhibitors, among the most widely used medications in the world, reduce stomach acid in a way that impairs B12 absorption. Metformin, the most common drug for type 2 diabetes, does the same through a different mechanism. H2 blockers, another class of acid-reducing drugs, contribute as well. A review of these interactions found that long-term use of all three drug classes was significantly associated with lower B12 levels, with metformin and proton pump inhibitor users showing a pattern where the risk grew with higher doses and longer use.²⁰

For an older adult taking a proton pump inhibitor for reflux and metformin for diabetes, the combined effect on B12 can be substantial. If that person then develops confusion, paranoia, or hallucinations, the correct diagnosis could easily be missed. The psychiatric symptoms might be attributed to dementia, delirium, or a primary psychotic disorder, while the true culprit sits in the daily pill organizer. This is one of the more practical takeaways from the literature: if you or someone you care for takes medications in these classes long-term, periodic B12 monitoring is a simple and inexpensive safeguard.

Inborn Errors of Metabolism

Beyond dietary deficiency, some people have genetic conditions that prevent their body from properly transporting or using certain vitamins regardless of how much they consume. These inborn errors of metabolism can produce psychiatric symptoms, including psychosis, that are indistinguishable from schizophrenia on clinical examination alone. A notable proportion of adults with certain metabolic conditions have been mistakenly diagnosed and treated as having psychiatric illness, usually because their initial presentation involved psychotic or schizophrenia-like symptoms.²⁴ The key clinical clue is often that these patients do not respond well to standard psychiatric treatment. Resistance to antipsychotic medication in a young patient presenting with psychosis should raise the question of whether something metabolic is being missed.

1
PubMed. Neuropsychiatric manifestations in vitamin B12 deficiency
2
PubMed. Vitamin B(12) deficiency manifested as psychosis without anemia
3
PubMed Central. Vitamin B12 Deficiency Presenting as Psychotic Symptoms in a Psychiatry Department
4
PubMed. Psychiatric manifestations of vitamin B12 deficiency: a case report
5
PubMed Central. Psychosis and Seizures Attributed to Severe Vitamin B12 Deficiency
6
PubMed Central. Nutritional Deficiencies and Clinical Correlates in First-Episode Psychosis: A Systematic Review and Meta-analysis
7
PubMed Central. Abnormalities in one-carbon metabolism in young patients with psychosis
8
PubMed Central. Blood-brain barrier dysfunction and folate and vitamin B12 levels in first-episode schizophrenia-spectrum psychosis
9
PubMed. Is there a causal link between folate status and schizophrenia? Evidence from genetic association studies
10
PubMed Central. Case report of mental disorder induced by niacin deficiency
11
PubMed Central. Pellagra: An Unusual Cause for Altered Mental Status
12
International Journal of Research in Medical Sciences. Pellagra induced psychosis: a rare presentation
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PubMed Central. Observations on the Clinical Features of the Wernicke–Korsakoff Syndrome
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PubMed Central / Springer Nature. B1 Vitamin Deficiency After Bariatric Surgery, Prevalence, and Symptoms: a Systematic Review and Meta-analysis
15
PubMed. Developmental exposure to vitamin D deficiency and subsequent risk of schizophrenia
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PubMed Central. Vitamin D and schizophrenia: 20 years on
17
Nature. Vitamin B6 deficiency hyperactivates the noradrenergic system, leading to social deficits and cognitive impairment
18
Psychiatric Annals. Psychiatric Manifestations of Modern Scurvy
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PubMed Central. Acute Psychosis as Presenting Symptoms of Vitamin B12 Deficiency
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The Egyptian Journal of Internal Medicine. Risk of Vitamin B12 Deficiency Associated with Proton Pump Inhibitors, Metformin, and H2 Blockers in Geriatric Patients
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PubMed. The Vitamins in Psychosis Study: A Randomized, Double-Blind, Placebo-Controlled Trial of the Effects of Vitamins B(12), B(6), and Folic Acid on Symptoms and Neurocognition in First-Episode Psychosis
22
PubMed. A randomized controlled trial of Vitamin D supplementation in Iranian patients with schizophrenia
23
PubMed Central. Vitamin supplementation in the treatment of schizophrenia
24
PubMed Central. Psychiatric signs and symptoms in treatable inborn errors of metabolism