Vitamin B12 is necessary for healthy blood cells and nerves, as well as DNA production. B12 is attached to protein in food, but stomach acid separates the two. Your body then combines vitamin B12 with intrinsic factor, a protein made by your stomach and needed for vitamin B12 absorption. Some people cannot make intrinsic factor, which leads to difficulty in absorbing vitamin B12. Your body stores the vitamin, so deficiencies caused by low intake are rare, but they can occur with celiac and other digestive diseases. Because the main dietary source of vitamin B12 is food from animal sources, a deficiency is a possibility with vegan diets.
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Vitamin B12 Test
You should be fasting for six to eight hours before a B12 blood test. Although reference ranges can vary from lab to lab, the normal readings for vitamin B12 are approximately 200 to 900 picograms per milliliter, or pg/ml, of blood. Below 200 pg/ml indicates deficiency. If your levels are this low, you likely have symptoms of deficiency. Older adults may have symptoms if their levels are below 500 pg/ml.
Symptoms of Vitamin B12 Deficiency
Symptoms of vitamin B12 deficiency include fatigue, weakness, loss of appetite, weight loss, constipation and soreness of the mouth or tongue. A deficiency can also cause neurological symptoms, such as numbness and tingling in the extremities, balance problems, depression, confusion, poor memory and dementia. Babies who are deficient in vitamin B12 may have failure to thrive, meaning they do not grow or gain weight as they should. They also may not reach developmental milestones as expected.
Complications of Vitamin B12 Deficiency
Megaloblastic anemia is a serious result of vitamin B12 deficiency. Red blood cells grow larger than is normal, meaning there are not enough healthy red blood cells, which leads to anemia. Megaloblastic anemia can also be caused by a folate deficiency, so folate testing is often done with a vitamin B12 test. Large amounts of folate supplementation can correct megaloblastic anemia and hide a vitamin B12 deficiency; however, neurological damage still occurs if the vitamin B12 deficiency is not addressed. Pernicious anemia is a form of megaloblastic anemia caused by your stomach not making intrinsic factor. Because lack of intrinsic factor makes it impossible to absorb vitamin B12, injections of vitamin B12 are needed.
From age 14 years and up, you need 2.4 mcg of vitamin B12 per day. If you are pregnant, your need increases to 2.6 mcg, and if breastfeeding, to 2.8 mcg. Up to six months of age, a baby needs 0.4 mcg and then 0.5 mcg until 1 year old. Children from 1 to 3 years need 0.9 mcg, from 4 to 8 years need 1.2 mcg and from 9 to 13 years need 1.8 mcg.
Dietary Sources of Vitamin B12
Vitamin B12 is found naturally only in foods from animal sources, including dairy products and eggs. Beef liver and clams contain the highest amount. Many packaged foods are fortified with vitamin B12. People who follow a strict vegan diet by avoiding all foods from animal sources and those who have absorption problems because of disease or surgery should talk to their doctor about vitamin B12 supplementation.