Vitamin B12, or cobalamin, is a vitamin that helps you break down food for energy. Your body uses it to form red blood cells and DNA. You also need it for proper neurological function and to make SAMe, a compound your body needs to make genetic material, proteins, hormones, and fats. Vitamin B12 is found in clams, liver, fortified cereal, fish, meat, dairy products, and eggs. A vitamin B12 deficiency may lead to fatigue, weakness, constipation, weight loss, loss of appetite, and neurological trouble including depression, memory problems, confusion, dementia, difficulty with balance, and numbness and tingling in the hands and feet. People at risk for B12 deficiency include those with gastrointestinal disorders that affect nutrient absorption (celiac disease, pernicious anemia, atrophic gastritis), vegetarians, and pregnant women or those who are lactating who are vegetarians. Their infants may suffer from B12 deficiency as well. People in these groups should take a vitamin B12 supplement.