Why are strict vegans at risk of vitamin B12 deficiency?

Strict vegans are at risk of vitamin B12 deficiency because this essential nutrient is found naturally only in animal-derived foods, such as meat, eggs, and dairy products.12

While vitamin B12 is synthesized by microorganisms, it is not produced by plants. Because vegans exclude all animal products from their diets, they cannot obtain the vitamin through standard food sources. To prevent deficiency, which can lead to serious health issues like megaloblastic anemia and irreversible nerve degeneration, it is essential for vegans to consume fortified foods or take vitamin supplements.12

It is important to note that although bacteria in the human colon also produce vitamin B12, it cannot be absorbed at that site, making dietary intake or supplementation necessary for those who do not consume animal products.3