Deficiency is common, especially in people who follow a vegetarian or vegan diet. In fact, it’s thought that up to 90% of people following these diets have a deficiency. This is because B12 is only found naturally in animal foods. However, vegans and vegetarians are not the only ones who are deficient. Even some meat eaters don’t absorb it very well. Unlike other vitamins, the absorption of vitamin B12 depends on a protein produced in your stomach, called intrinsic factor. Intrinsic factor binds to vitamin B12, so that you can absorb it into the blood. People who don’t produce enough intrinsic factor can become deficient. Deficiency is particularly common in elderly people, because the ability to absorb vitamin B12 can decrease with age. Other people at risk of deficiency include those who have had intestinal surgery, including weight loss surgery or those with diseases that affect the gut, such as Crohn’s disease or celiac disease, are also at risk.