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Beware of B12 deficiency


April 21, 2017

As noted in last week’s column about vitamin D, vitamins are substances that the body can’t make that are necessary in trace amounts for normal metabolic functioning. Vitamin B12 (cobalamin) is a water-soluble vitamin (as opposed to fat-soluble). Unlike other vitamins, which are made by plants (vitamin D is an exception because it is produced by exposure to sunlight), B12 comes from bacteria in dirt. Animals eat food that contains dirt, and B12 is stored in their livers and muscles. B12 also ends up in eggs and dairy. The average adult needs 2.3 micrograms of B12 a day, which is adsorbed in the lower part of the small intestine (ileum). Intrinsic factor, made by parietal cells in the stomach, is necessary for absorption.

B12 is involved in every cell in the human body and in particular it is necessary for brain, nervous system and red blood cell health. Deficiency in B12 can result in the following health problems:

Anemia associated with abnormally large red blood cells.


Numbness and tingling in hands and feet, poor balance, which can be irreversible.

Memory trouble, depression and even psychosis.

Elevated homocysteine, a risk factor for cardiovascular disease.

For the most part, people who eat animal products do not experience B12 deficiency. However, the following conditions can result in deficiency, even if intake is adequate:

Pernicious anemia, which is an autoimmune disease that destroys the intrinsic factor necessary for B12 absorption.

Obesity surgery such as stomach stapling, and other GI tract surgery involving the stomach or small intestine.

Celiac and severe Crohn’s disease.

The commonly-used diabetic drug metformin.

Drugs that prevention secretion of stomach acid taken for more than two years (PPIs such as Nexium and Prilosec; H2 blockers such as Pepcid and Zantac).

Advanced age: people 65 and older don’t absorb B12 as well.

In addition, a vegan lifestyle can result in deficiency. People often ask me why, if plant-based nutrition is a “natural” diet, they have to take a B12 supplement. The answer is that we don’t eat as much dirt, with B12-containing bacteria, as we did when the human genome was evolving. For example, our water is treated (which is a good thing in that we don’t get cholera or giardia). And our produce is often pre-washed.

How do you tell if you are deficient in B12? If you have any of the symptoms of B12 deficiency noted above, if your red blood cells are abnormally large, or if you have any of the above risk factors for deficiency, you should have a blood test done to check your level of B12. A more accurate test is a serum methylmalonic acid.

Deficiency is treated with supplements. For the most part, oral supplements are sufficient. In rare situations such as Celiac disease or severe Crohn’s disease injections are necessary. To prevent deficiency, all vegans should supplement with 250 micrograms a day of B12 (cyanocobalamin), which is inexpensive and which you can buy at any drug store in pill form (sublingual preparations offer no advantage). People 65 and older should take 1,000 micrograms a day. It is especially important that vegan women who are pregnant supplement, to ensure that the growing fetus gets adequate B12. Unlike other vitamins, you can’t get too much vitamin B12 with oral supplementation because you can only absorb a certain amount.

Years ago doctors would give B12 injections to patients who complained of feeling tired. However this practice is a bad idea. There are many causes of feeling tired, and B12 deficiency is an uncommon one. So if you feel tired, you need a workup to see what the cause is and then you should be treated appropriately.


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