Brain fog with no obvious cause is one of the more frustrating symptoms to investigate. Vitamin B12 deficiency is a common contributor and one of the easier to check. Levels can be low long before classic anaemia symptoms appear, which is why testing matters.
Why B12 affects brain function
B12 is essential for the protective myelin sheath around nerves and for several brain biochemistry pathways. Deficiency can cause fatigue, brain fog, memory problems, tingling or numbness, mood changes and, in severe cases, irreversible nerve damage if untreated.
Who is at higher risk
Vegans and strict vegetarians (B12 is found almost exclusively in animal foods). Adults over 50 (stomach acid naturally declines, reducing B12 absorption). People on long-term metformin or proton pump inhibitors. Those with coeliac disease, Crohn's or gastric surgery.
What level is enough
UK NHS thresholds classify B12 below 150 ng/L as deficient and above 200 ng/L as adequate. Many clinicians prefer levels above 400 ng/L for optimal nervous system function. Active B12 (holotranscobalamin) is a more sensitive marker when results are borderline.
Treatment options
Oral B12 supplements (cyanocobalamin or methylcobalamin) work well for most people. Pernicious anaemia (autoimmune destruction of B12 absorption) typically needs B12 injections under medical supervision. Chxhealth is a biomarker and genetic data provider. We do not diagnose, treat or prescribe. Our service supports your wellbeing journey alongside your healthcare professional.
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Frequently asked questions
Should I supplement B12 if I am vegan?
Yes. The NHS recommends a daily B12 supplement for vegans and strict vegetarians. Test if you have not been supplementing and have symptoms.
Why does metformin lower B12?
Metformin interferes with B12 absorption in the small intestine. Up to 30 percent of long-term users develop B12 deficiency. Annual testing is recommended.
About this article. Educational content. Chxhealth is a biomarker and genetic data provider. We do not diagnose, treat or prescribe. Our service supports your wellbeing journey alongside your healthcare professional. For medical advice about your health or results, please speak to a qualified clinician.
