Counseling Sheet

Vitamin B12

Agatha M. Thrash, M.D.

Preventive Medicine

The small intestine of healthy humans can contain bacteria that are capable of producing vitamin B12. There are at least two groups of germs normally in the small bowel: Pseudomonas and Klebsiella. These may synthesize significant amounts of the vitamin, high enough in the intestinal tract to be absorbed in the terminal ileum (Nature 283:781; February 21, 1980). Both these germs can overgrow and cause an unhealthy small bowel.

Around 3,000 men and women aged 26-83, investigated as a part of the Framingham offspring study, showed a surprising 39 percent of the participants to have blood levels of B12 below 350, the level at which neurological signs of vitamin B12 deficiency or high homocysteine levels sometimes occur. Younger people were just as likely to have low levels as older people. Those who got their B12 from supplements or fortified breakfast cereals or dairy products were less likely to be deficient than those who got their B12 from dairy products, meat, poultry, or fish. It was suggested by the researchers that the proteins in meat may make B12 less available. The RDA for B12 is from 6-25 micrograms, depending on the age, the higher levels being in older people (American Journal of Clinical Nutrition 71:51, 2000).

Factors that Affect B12 Needs

  1. Meat, other animal products, and refined carbohydrates (sugars) when used generously may more than double the amount of B12 you must have from all your sources to stay healthy.
  2. Persons who use drugs, chemicals, or beverages that destroy B12 (tobacco, alcohol, caffeine, etc.), will require more B12 to stay healthy.
  3. Megadoses of vitamin C may produce B12 deficiency by destroying the cobalamins during the time both B12 and vitamin C are in the intestinal tract together. More than 500 milligrams of vitamin C can destroy 50-95 percent of B12 in the intestinal tract. If both vitamin C and B12 must be taken for some condition, B12 should be taken at the beginning or before the meal, and vitamin C should be taken after meals.
  4. Oral contraceptives increase the need for vitamin B12.
  5. Cooked eggs decrease B12 absorption.
  6. Intestinal parasites, especially tape worms, and explosively growing bacteria in the intestinal tract such as from infected or inflamed intestines, can effectively compete with the host for B12 and make the requirements higher. Helicobacter pylori infection can cause malabsorption of vitamin B12.
  7. Almost 90 percent of older people with serum B12 levels less than 150 show evidence of tissue vitamin B12 deficiency. Older people are more subject to disability from low B12 than younger individuals (Journal of the American Geriatric Society 44:1355;1996). We can see wisdom for persons over age 60 with low B12 levels taking a supplement. About 100 micrograms daily chewed for two minutes before swallowing (to get the "salivary factor") will probably be enough to supply the system with all its needs.

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