Why is vitamin B12 important to vegetarians?
Vitamin B12, an essential B vitamin, is of special interest to vegetarians since it is not found in any significant amounts in plant foods. In addition, vitamin B12 deficiency can result in detrimental changes in certain body functions. It is required for the normal maturation of red blood cells and also for the synthesis of the myelin sheath of nerve tissue.
Vitamin B12 deficiency manifests itself in a number of ways. Bone marrow makes fewer red blood cells and many of the cells that form are large and immature resulting in macrocytic anemia. The blood levels of B12 may decrease below normal levels.What are the signs of deficiency?
Other characteristic features seen with B12 deficiency include paresthesia (numbness and tingling in the hands and legs), inability to maintain balance when walking, weakness and excessive fatigue, loss of vibration and position sense, irregular menstrual cycles, and a range of psychiatric disorders including disorientation, depression, mood disturbances, irritability, memory loss, and dementia. Vitamin B12 deficiency is fairly common in the elderly and is associated with dementia and other neurological disorders seen in the geriatric population.
For years it was believed that the first sign of vitamin B12 deficiency wasmegaloblastic anemia characterized by large, immature red blood cells. There have been reports recently of neurologic damage due to B12 deficiency occurring in patients without anemia. The neurologic abnormalities due to B12 deficiency were corrected by vitamin B12 therapy. Neurological damage may require weeks and months of recovery or may be too advanced for recovery.
Does this affect all vegetarians?
Reports from around the world reveal that may long-term total vegetarians (vegetarians who do not use any eggs, meat, fish, poultry or dairy products) are especially at risk of vitamin B12 deficiency. Unfortunately, many total vegetarians fail to recognize the seriousness of B12 deficiency.
Total vegetarians often have low serum B12 levels and may manifest neuropsychiatric disorders. While oral B12 supplements can restore serum levels of B12 and eliminate macrocytic anemia, the neurological disorders may persist even months after treatment. In some cases the damage done to the nervous system is not reversible.
On rare occasions a lacto-ovo-vegetarian (one that uses dairy products and eggs, but no meat, fish or poultry) may also have a low serum B12 level if their intake of vitamin B12 containing foods is very low. Most of those with low serum B12 levels can correct the macrocytic anemia with oral B12 supplements or an injection of B12.
In one study, the serum B12 levels of adult lacto-ovo-vegetarians dropped 35 percent only two months after switching to a total vegetarian diet. This rapid drop may be the result of low B12 stores in the liver. It should be emphasized, however, that vitamin B12 deficiency most often occurs in total vegetarians.
What causes vitamin B12 deficiency?
Although vitamin B12 deficiency may result from a number of factors, the major reason is lack of adequate B12 absorption. In order to be absorbed in the small intestine, vitamin B12 in food must be combined with an intrinsic factor-a protein made by the stomach. Receptors for B12 absorption occur in the ileum, the lowest portion of the small intestine. Adults secrete about 5-7 micrograms of B12 in the bile daily. Normally we reabsorb most of this. As long as vitamin B12 absorption is effective, a deficiency may not readily develop. However, it can take only about three years to become B12 deficient if one stops absorbing the vitamin.
The lack of B12 absorption usually results from:
A lack of B12 in the diet because of poor food selection.
A lack of intrinsic factor secretion due to aging, gastritis, or the partial removal of the stomach by surgery (gastrectomy).
Lack of hydrochloric acid in the stomach, especially in the elderly.
Ileal (small bowel) resection or ileitis.
Vitamin B12 deficiency in humans may be slow to develop because of large liver stores. Typical American diets contain about 5-15 micrograms per day, allowing substantial liver storage to take place. It is estimated that about 3000 micrograms are stored in an adult, and 30-50 micrograms are stored in an infant or child. Persons who completely give up animal products may go for years before showing any signs and symptoms of a B12 deficiency or before any nervous system disorders are manifest.
From what sources is vitamin B12 available?
Vitamin B12 is made by bacteria and fungi, but not by yeasts or higher plants. Friendly bacteria resides in large quantities in the gastrointestinal tract of animals and humans. Since the manufacturing site of B12 in humans is not located where absorption occurs, humans can not rely on its availability. The total vegetarian must find vitamin B12 from other reliable sources.
For the lacto-ovo-vegetarian, reliable sources would include dairy products and eggs which can supply substantial amounts of B12. For example, one cup of milk contains 0.9 micrograms of vitamin B12 while 8 ounces of yogurt has 1.5 micrograms. Sterilized, boiled, or canned milk destroys about one-half of the vitamin B12.
Since most of the vitamin B12 resides within the cholesterol-laden yolk, it would be better for the lacto-ovo-vegetarian to rely on low-fat dairy products for their source of B12. Vegetarians who use a B12 supplement should ensure that it contains an active form of the vitamin-namely, cyanocobalamin or hydroxocobalamin.
Fermented soy products, such as miso and tempeh, shiitake (dried mushrooms) and algae such as spirulina and nori contain practically no vitamin B12. While these foods are often sold in health food stores as “excellent souces of B12” and are widely used by the macrobiotic community, they actually contain little, if any active B12 (cobalamin). Instead they contain analogs of B12 that are not active and may actually block the absoprtion of true vitamin B12.
What Are B12 Intake Recommendations for Vegetarians?
The General Conference Nutrition Council recommends the total vegetarian should include fortified food high in vitamin B12 or use a vitamin B12 supplement. This would be especially true of one who is pregnant or breast-feeding a child.
During the latter half of pregnancy the fetus removes significant amounts of B12 from the mother’s stores, and a nursing mother secretes vitamin B12 in her breast milk. Without adequate fetal stores and low breast milk levels, blood levels of vitamin B12 may fall to very low levels, especially in the offspring of a total vegetarian consuming a diet without any B12 sources.
An infant born to a mother who has been a total vegetarian for many years is clearly at high risk of vitamin B12 deficiency. Even though the mother may not show signs of vitamin B12 deficiency, her fetus may not receive adequate intake of the vitamin since most of the infant’s B12 stores comes from the mother’s diet during pregnancy rather than from her stores. Vitamin B12 deficiency may develop in the breast-fed infant within 3-6 months of age. The B12 deficient child may have seizures, become apathetic, lethargic, anemic, and show signs of developmental delay and failure to thrive.
Since there isn’t a reliable and adequate souce of vitamin B12 in plant foods, total vegetarians should obtain their dietary needs either from foods fortified with B12, such as some fortified ready-to-eat cereals, fortified soy beverages, fortified meat analogs, or from the regular use of a vitamin B12 supplement.
A B12 supplement of five micrograms taken daily is probably adequate. Some suggest that B12 supplements should be thoroughly chewed for better absorption. As mentioned earlier, the B12 supplement for the total vegetarian should contain an active form of cyanocobalamin or hydroxocobalamin.
Seaweed and soy products do not contain significant levels of active B12 despite the claims made for such products. The basis for the erroneous claims stems from the fact that the method that is often used to measure B12 does not distinguish between the active and inactive forms of the vitamin.
To prevent the risk of psychiatric problems and permanent neurological damage, a total vegetarian who avoids all animal products should have their serum B12 levels checked periodically. Total vegetarians who are pregnant should rooutinely have their serum B12 levels checked. Anyone found to have a serum B12 level below 300 pg/ml should be tested for urinary methylmalonate levels.
For the lacto-ovo-vegetarian the present recommended dietary allowance is two micrograms per day for adults and teenagers, about 2.5 micrograms of pregnant and breast feeding women and one microgram or less for children. The lacto-ovo-vegetarian should consume a variety of foods actually containing B12 such as low-fat milks and yogurts and/or B12 fortified foods such as commercial cereals, meat analogs, and soymilks.