Everything You Wanted to Know About B12 (Part 1)

In this comprehensive episode of Nutrition Facts with Dr. Michael Greger, the critical importance of vitamin B12 for plant-based eaters is explored in depth. Dr. Greger emphasizes that B12 deficiency can lead to severe neurological, psychiatric, and life-threatening conditions—including coma, psychosis, and irreversible nerve damage—especially in infants born to unsupplemented mothers. Despite widespread recommendations, there is no consensus on how quickly deficiency develops in those avoiding animal products, with estimates ranging from weeks to decades, but evidence from bariatric surgery patients and real-world cases shows functional deficiency can emerge in months. The episode highlights the limitations of standard blood tests, which often fail to detect true deficiency due to variability, false negatives, and the fact that symptoms can occur even with 'normal' B12 levels. Functional markers like methylmalonic acid (MMA) and homocysteine are more reliable but still influenced by other factors like kidney function and folate levels. The discussion concludes with a strong endorsement of B12 supplementation as the only reliable prevention strategy, debunking myths about plant sources like chlorella, spirulina, and nori, which often contain unusable pseudo-B12 or are contaminated. Dr. Greger also clarifies that cyanocobalamin is the most effective and cost-efficient form for most people, countering misleading claims from AI and supplement marketing.