Vitamin B12

Dear Dr. B: Thank you for your columns on Vitamin C and other vitamins. What about vitamin B12? Many people are on B12 injections on regular basis. Why is B12 important? Yours, Ms. B12.

Dear Ms. B12: Vitamin B12 deficiency is a common problem that affects the general population and the elderly in particular. Persons with the deficiency may have no symptoms or may have symptoms related to blood disorder or disorders of the nervous system including psychiatric problems.

Vitamin B12, also known as cobalamin, was first isolated in 1948 and was immediately shown to be effective in the treatment of pernicious anaemia. Recently, interest in the vitamin has been renewed because of the recognition that B12 deficiency occurs in 3% to 40% of the general population.

Vitamin B12 is essential for good health. It is obtained primarily from animal proteins (i.e., red meat, poultry, fish, eggs, and dairy). But the vegetarians can get enough of it from legumes. The cause of B12 deficiency is not usually poor diet but problems with absorption in the gastro-intestinal tract.

Absorption of vitamin B12 from foods is complex; a defect in any step can lead to deficiency. In the stomach, gastric acid and pepsin is required for digestion of B12. In the upper small intestine, pancreatic enzymes and an alkaline pH is necessary. B12 is absorbed from the terminal ileum (last part of the small intestine where it joins the colon).

The liver contains most of the body’s B12 (about 1.5 mg), followed by the kidneys, heart, spleen, and brain. Normal body stores of vitamin B12 range from 2 to 10 mg; daily losses are 2 to 5 micrograms. The stored B12 can last us two years in conditions where our body is deprived of B12.The latest Recommended Dietary Allowance (RDA) for vitamin B12 is 2.4 micrograms/day for persons aged 14 to 70 years; the average diet contains about 5 micrograms daily.

The diagnoses of B12 deficiency is made by checking the blood levels in patients who have symptoms or who are prone to B12 deficiency. Treatment is by B12 injections on regular basis for the rest of person’s life.


A reader wants to know the following:

What is the difference between micrograms (ugm.), milligrams (mg.) and International Units (IU)?

1000 micrograms is 1 milligram.

International unit (IU):
Is a unit used to measure the activity (that is, the effect) of many vitamins and drugs. For each substance to which this unit applies, there is an international agreement specifying the biological effect expected with a dose of 1 IU. Other quantities of the substance are then expressed as multiples of this standard. Examples: 1 IU represents 45.5 micrograms of a standard preparation of insulin or 0.6 microgram of a standard preparation of penicillin. Consumers most often see IU’s on the labels of vitamin packages: in standard preparations the equivalent of 1 IU is 0.3 microgram (0.0003 mg) for vitamin A, 50 micrograms (0.05 mg) for vitamin C, 25 nanograms (0.000 025 mg) for vitamin D, and 2/3 milligram for vitamin E. Please note: for many substances there is no definite conversion between international units and mass units (such as milligrams). This is because preparations of those substances vary in activity, so that the effect per milligram of one preparation is different from that of another.

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