Vitamin B12 Deficiency in Plant-Based Diets

Risk Assessment and Clinical Significance

Strict vegans and vegetarians are at high risk of vitamin B12 deficiency, which can lead to serious and potentially irreversible neurological damage if left undetected, according to the British Medical Journal guidelines 1, 2
Vitamin B12 occurs in substantial amounts only in foods derived from animals, making it unavailable in plant-based diets unless fortified or supplemented, as stated by the Critical Reviews in Food Science and Nutrition 2
Deficiency can lead to serious neurological complications including peripheral neuropathy, balance issues, impaired gait, and cognitive difficulties, as reported by the British Medical Journal 1
Other manifestations include macrocytic anemia, optic neuropathy, glossitis, and unexplained fatigue, as noted by the British Medical Journal 1

First-line testing should include either total B12 (serum cobalamin) or active B12 (serum holotranscobalamin), as recommended by the British Medical Journal and Praxis Medical Insights 1, 3
Active B12 measures the biologically active form available for cellular use and may be more accurate, though more expensive, according to the British Medical Journal and Praxis Medical Insights 1, 3

Certain medications (colchicine, H2 receptor antagonists, metformin, phenobarbital, pregabalin) can further increase the risk of B12 deficiency in vegetarians, as reported by the British Medical Journal and Praxis Medical Insights 1, 4
Normal serum B12 levels may not accurately reflect tissue stores, potentially masking functional deficiency, as noted by Praxis Medical Insights 3