Vitamin B12 deficiency is common in vegan diets because B12 is naturally found almost exclusively in animal products, and plant foods typically lack reliable active forms, making it difficult to meet needs without fortification or supplements; this can lead to issues like anemia, fatigue, nerve damage, and cognitive problems, since B12 plays a key role in red blood cell formation, DNA synthesis, and nervous system function. Vegans can meet their needs through B12-fortified foods such as plant milks, breakfast cereals, and nutritional yeast, or by taking supplements like cyanocobalamin or methylcobalamin. To prevent deficiency, it’s recommended to take regular supplements (e.g., 250–500 mcg daily or 2000 mcg weekly), check levels periodically via blood tests (including B12 and homocysteine), and maintain consistent intake, as relying solely on unfortified plant foods is not a dependable strategy for long-term health.