The body needs vitamin B-12, a nutrient naturally present in most animal products, to produce red blood cells, metabolize fat and protein and maintain proper neurological function. Inadequate intake or absorption of vitamin B-12 can lead to vitamin B-12 deficiency anemia, a condition with potentially serious side effects. Excess vitamin B-12, on the other hand, is unlikely to cause adverse effects, according to the Institute of Medicine.
Tolerable Upper Intake Level
The Institute of Medicine establishes a tolerable upper intake level, or UL, for nutrients that can cause adverse effects in large amounts. The UL value represents the highest daily intake of a nutrient or substance that would not be likely to cause adverse effects in most of the population. The Institute of Medicine did not establish a UL value for vitamin B-12, because no evidence suggests that this nutrient causes adverse effects.
Recommended Daily Intake
Adolescents and adults ages 14 and older should get 2.4 mcg of vitamin B-12 per day, according to the National Institutes of Health Office of Dietary Supplements. Pregnant women should get 2.6 mcg per day, and lactating women should get 2.8 mcg. Food sources of vitamin B-12 include beef liver, clams, fortified cereals, salmon, trout, haddock, tuna, turkey and milk.
Vitamin B-12 Deficiency
Vitamin B-12 deficiency causes symptoms of weakness, fatigue, dizziness, shortness of breath, difficulty concentrating, pale skin, sore tongue, constipation and weight loss. Long-term vitamin B-12 deficiency can cause nerve damage or neurological changes, with symptoms such as numbness or tingling in hands and feet, confusion, difficulty maintaining balance, depression, poor memory and dementia.
Need for Vitamin B-12 Supplements
Data from the Framingham Offspring Study shows that individuals who take vitamin B-12 supplements or eat fortified cereals more than four times per week are less likely to have vitamin B-12 deficiency, according to the National Institutes of Health Office of Dietary Supplements. Individuals at risk for vitamin B-12 deficiency should consider taking a supplement. Vegetarians and vegans who do not eat animal products may not get enough vitamin B-12 in their diets. A variety of health conditions can hinder the body's absorption of vitamin B-12, including atrophic gastritis, pernicious anemia, celiac disease and Crohn's disease.
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