Can B12 cause anxiety? This question arises as more people take vitamin B12 supplements for deficiency or general wellbeing. Vitamin B12 (cobalamin) is essential for neurological function, DNA synthesis, and red blood cell formation. Whilst B12 deficiency is well known to cause psychiatric symptoms including depression and cognitive impairment, concerns about whether adequate or elevated B12 levels might trigger anxiety require careful examination. This article explores the scientific evidence, clarifies when B12 supplementation might be associated with anxiety-like symptoms, and provides guidance on safe management aligned with UK clinical practice and NICE recommendations.

Understanding Vitamin B12 and Its Role in Mental Health

Vitamin B12 (cobalamin) is an essential water-soluble vitamin that plays a crucial role in numerous physiological processes, including DNA synthesis, red blood cell formation, and neurological function. Within the central nervous system, B12 is vital for maintaining the myelin sheath that protects nerve fibres and for methylation processes that support neurological function, indirectly affecting neurotransmitters involved in mood regulation.

The relationship between B12 and mental health is well established in medical literature, though it is primarily characterised by the psychiatric consequences of deficiency rather than excess. Low B12 levels have been associated with depression, cognitive impairment, irritability, and in severe cases, psychosis. The vitamin's role in homocysteine metabolism is particularly relevant—deficiency leads to elevated homocysteine levels and methylmalonic acid, which may contribute to neurological dysfunction.

B12 is obtained exclusively from animal-derived foods (meat, fish, dairy, eggs) or fortified products, making vegans and vegetarians particularly vulnerable to deficiency. Other risk groups include older adults, pregnant women, people taking metformin or long-term acid-suppressing medications (PPIs, H2 blockers), those with conditions affecting the gastrointestinal tract (pernicious anaemia, Crohn's disease, coeliac disease), and individuals who have undergone gastric or ileal surgery. The body stores B12 in the liver, with reserves typically lasting several years. However, absorption requires intrinsic factor, a protein produced in the stomach.

Understanding B12's neurological importance helps contextualise concerns about its potential effects on anxiety. Whilst deficiency clearly impacts mental health, the question of whether adequate or elevated B12 levels might paradoxically cause anxiety requires careful examination of the available evidence.

Can B12 Cause Anxiety? Examining the Evidence

The short answer is that there is no established scientific evidence that vitamin B12 supplementation or elevated B12 levels directly cause anxiety in most individuals. The overwhelming body of research focuses on deficiency-related psychiatric symptoms rather than toxicity or adverse effects from adequate intake. B12 is a water-soluble vitamin, meaning excess amounts are typically excreted in urine rather than accumulating to toxic levels, which distinguishes it from fat-soluble vitamins like A and D.

However, some individuals report experiences that suggest possible associations between B12 and anxiety-like symptoms in certain contexts:

• High-dose supplementation: Some individuals report feeling 'overstimulated' or experiencing changes in energy levels when initiating B12 supplements. However, these reports are largely anecdotal and not substantiated by controlled clinical studies.

• Underlying deficiency correction: When severe B12 deficiency is corrected, some patients experience temporary neuropsychiatric symptoms as nerve function recovers—a phenomenon sometimes called 'unmasking' of symptoms.

• Individual variation: People may respond differently to supplements based on their underlying health status, though controlled studies examining formulation-specific effects on anxiety are lacking.

Elevated serum B12 levels (hypercobalaminaemia) detected on blood tests may indicate underlying conditions such as liver disease, kidney dysfunction, or myeloproliferative disorders rather than representing a direct cause of symptoms. Unexplained persistent high B12 levels should prompt evaluation for these conditions.

According to MHRA product information for hydroxocobalamin (the standard injectable form used in the UK), common side effects include injection site reactions and occasional hypersensitivity reactions, but anxiety is not listed as a recognised adverse effect of B12 supplementation.

When to Seek Medical Advice About B12 and Anxiety Symptoms

If you are experiencing anxiety symptoms—whether or not you suspect a connection to B12 supplementation—it is important to seek appropriate medical evaluation. Contact your GP if you experience:

• Persistent anxiety, panic attacks, or mood changes that interfere with daily functioning

• Physical symptoms accompanying anxiety, such as palpitations, chest tightness, breathlessness, or dizziness

• Neurological symptoms including numbness, tingling (paraesthesia), balance problems, or memory difficulties

• Symptoms that began shortly after starting B12 supplements or changing dosage

• Concerns about potential B12 deficiency (fatigue, pallor, glossitis, cognitive changes)

Your GP can conduct a thorough assessment including medical history, medication review, and physical examination. Blood tests may be arranged to evaluate:

• Serum B12 levels (though interpretation can be complex, as levels may appear normal despite functional deficiency)

• Full blood count (to identify macrocytic anaemia)

• Folate levels (often checked alongside B12)

• Intrinsic factor antibodies and possibly parietal cell antibodies (to identify pernicious anaemia)

• Methylmalonic acid or holotranscobalamin (for borderline B12 cases)

• Thyroid function (as thyroid disorders commonly cause anxiety)

• Liver and kidney function tests if B12 is unexpectedly high

According to NICE Clinical Knowledge Summaries, B12 deficiency should be considered in people with unexplained macrocytosis, neuropathy, cognitive changes, or glossitis. If you are taking B12 supplements and suspect they may be contributing to anxiety, do not abruptly discontinue without medical advice, particularly if you have been diagnosed with deficiency. Your GP can help determine whether supplementation is necessary and advise on appropriate dosing.

Call 999 or go to A&E immediately if you experience severe chest pain, severe confusion, or have immediate thoughts of harming yourself. For urgent but non-life-threatening concerns, contact NHS 111 or the NHS urgent mental health helpline. The Samaritans (116 123) also provide 24/7 emotional support.

Managing B12 Levels Safely in the UK

Safe management of B12 status involves appropriate testing, evidence-based supplementation when indicated, and regular monitoring. The reference nutrient intake (RNI) for adults in the UK is 1.5 micrograms daily, though therapeutic doses for treating deficiency are substantially higher.

Diagnosis and treatment of deficiency follows established protocols. NICE and British Society for Haematology guidelines recommend:

• Initial treatment with hydroxocobalamin (the preferred form in the UK) via intramuscular injection

• For patients without neurological involvement: 1 mg IM three times a week for 2 weeks

• For patients with neurological involvement: 1 mg IM on alternate days until no further improvement

• Maintenance: 1 mg every 3 months for patients without neurological involvement; every 2 months for those with neurological symptoms

• Oral supplementation (50–150 micrograms daily) may be appropriate for dietary insufficiency in patients with normal absorption; higher-dose oral therapy (1,000–2,000 micrograms daily) may be considered as an alternative to injections in selected cases with adequate absorption

For those taking supplements, consider these safety principles:

• Use supplements only when clinically indicated (confirmed deficiency or high-risk groups such as vegans, elderly, or those with malabsorption)

• In the UK, hydroxocobalamin is the preferred injectable form

• Avoid mega-doses without medical supervision; whilst B12 toxicity is rare, unnecessarily high doses offer no additional benefit

• Be aware of interactions: metformin and acid-suppressing drugs can reduce B12 levels; chloramphenicol may impair response to B12 therapy; nitrous oxide exposure can inactivate B12

• Important: Do not take folic acid alone when B12 deficiency is possible or uncorrected, as this may worsen neurological damage

• Avoid measuring serum B12 immediately after injections due to falsely high results

Dietary optimisation remains the preferred approach for those without absorption issues. Excellent sources include liver, oily fish (salmon, mackerel), meat, eggs, and dairy. Fortified foods (breakfast cereals, plant-based milk alternatives) provide options for vegetarians and vegans.

If you experience unexpected symptoms whilst taking B12, discuss with your GP whether continued supplementation is necessary or whether dose adjustment might help. Report suspected side effects via the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk or the Yellow Card app). Regular monitoring ensures B12 levels remain within the therapeutic range whilst minimising potential adverse effects.

Frequently Asked Questions