How Much Vitamin B12 Can You Have Per Day?

The body needs vitamin B-12, a water-soluble vitamin found in many animal products, to produce healthy red blood cells, synthesize DNA, metabolize protein and fat and maintain healthy neurological function. Many factors limit the body's absorption of vitamin B-12. As a result, vitamin B-12 has a very low potential for toxicity, and no evidence suggests that it causes adverse health effects.

Upper Intake Level

The Institute of Medicine of the National Academies has not established a Tolerable Upper Intake Level, or UL, for vitamin B-12 because of the low potential for adverse effects from this nutrient. Studies have found that doses of vitamin B-12 as high as 0.4 mg, or 4,000 mcg, have not caused adverse effects when administered for as long as 40 months, reports the National Institutes of Health Office of Dietary Supplements.

Recommended Intake

Recommended Dietary Allowances for vitamin B-12 vary according to age. Children ages 1 to 3 should get 0.9 mcg per day, children ages 4 to 8 should get 1.2 mcg day and children ages 9 to 13 should get 1.8 mcg per day, according to the National Institutes of Health Office of Dietary Supplements. Adolescents and adults ages 14 and over should get 2.4 mcg per day, while pregnant women should get 2.6 mcg per day and lactating women should get 2.8 mcg per day.

Food Sources

Vitamin B-12 exists naturally only in animal products. Good sources of vitamin B-12 include beef liver, clams, trout, salmon, haddock, yogurt, milk, cheese and eggs. Many fortified breakfast cereals contain synthetic vitamin B-12, a form of B-12 more easily absorbed by some people. Dietary supplements also contain synthetic vitamin B-12.

B-12 Deficiency Risk

Vitamin B-12 deficiency poses a much more serious risk than excess vitamin B-12. Vitamin B-12 deficiency can cause anemia, with symptoms such as weakness, fatigue and shortness of breath. Other symptoms of vitamin B-12 deficiency include constipation, loss of appetite, weight loss and sore tongue. Prolonged vitamin B-12 deficiency can damage neurological function, causing depression, memory loss, confusion and dementia. Individuals at high risk for vitamin B-12 deficiency include vegetarians and vegans and people with pernicious anemia, atrophic gastritis, Crohn's disease, tropical sprue and celiac disease.