Vitamin B-12 is one of the B-complex family vitamins along with riboflavin, thiamin, niacin, vitamin B-6, pantothenic acid and folate. You need vitamin B-12 for normal nervous system function, formation of DNA and for regular red blood cell production. The recommended daily allowance, or RDA, for vitamin B-12 increases with age and in women who are pregnant or breastfeeding.
RDA for Adults
The U.S. Institute of Medicine sets the RDA for vitamins and minerals. The RDA for vitamin B-12 is 2.4 micrograms per day for adults. Women who are pregnant need 2.6 micrograms per day, and women who are breastfeeding need 2.8 micrograms per day. The Institute of Medicine also sets the tolerable upper limit, or UL, for nutrients, however, there is no UL for vitamin B-12 because according to the institute, no adverse effects are associated with large B-12 intakes.
RDA for Children
The Institute of Medicine doesn’t determine an RDA for vitamin B-12 for infants, but uses an adequate intake, or AI, instead. The AI is the amount believed to be sufficient. The AI is 0.4 micrograms per day for infants up to 6 months of age and 0.5 micrograms for infants up to 12 months of age. The RDA is 0.9 micrograms per day for children ages 1 to 3 years, 1.2 micrograms for ages 4 to 8 years, and 1.8 micrograms for children 9 to 13 years. Teens through age 18 need 2.4 micrograms per day.
Foods of animal origin contain vitamin B-12, so most diets provide more than enough vitamin B-12. Clams and beef liver contain more than 1,000 micrograms per serving. A 3-ounce serving of trout or salmon provides at least half of your RDA. Beef, milk, yogurt, cheese, ham, eggs and chicken are also good sources. Vegans, or strict vegetarians, may need to take supplements or choose vitamin-fortifed cereals because vitamin B-12 is not present in plant foods.
Vitamin B-12 Deficiency
Vitamin B-12 deficiency causes anemia, which means your red blood cells can't carry enough oxygen to all the parts of your body. Deficiency symptoms include fatigue, weakness, appetite loss, unexpected weight loss and constipation. Vegans and strict vegetarians can prevent deficiency by taking B-12 supplements to meet the RDA. However, deficiency is usually caused by diseases that reduce your ability to absorb vitamin B-12, rather than a lack of dietary sources, so speak to your doctor if you believe you have a B-12 deficiency.
Sheri Kay has a master's degree in human nutrition. She's the co-author of two books and has been a nutrition and fitness writer since 2004.