How Much Vitamin B12 Should I Be Taking?

I have anemia and ataxia and want to know how much vitamin B12 I should be injecting. My doctor is having me inject only 100mcg per month. That doesn’t seem like much, and after six months or more I have noticed no improvement in my ataxia. I am also having hearing problems.

I am assuming you have pernicious anemia, which causes anemia, can cause neurological problems including ataxia, and is treated with monthly injections of vitamin B12.

Pernicious anemia is an autoimmune disease, in which antibodies formed by the immune system slowly destroy the cells in the stomach that produce a substance known as intrinsic factor. Intrinsic factor is required for adequate absorption of B12 in the intestine. The disease usually appears insidiously, meaning that the symptoms develop gradually, and may not be noticed. Most of us have large stores of B12 in our bodies built up during the years when we did absorb it well, and therefore it may take several years after we stop absorbing the vitamin before any symptoms develop. Vitamin B12 is only available from animal sources. Strict vegans who eat nothing of animal origin will not take in any B12. Surprisingly this usually does not lead to anemia, either because they have large stores of the vitamin built up before they became vegans, or because they are often aware of this problem and take an oral B12 supplement. Infants born to strict vegans have been reported with this anemia, probably because they do not get an adequate supply of the vitamin from their mothers during intrauterine development, and then may get none after birth if they are also fed a strict vegan diet. The vitamins normally given to infants do not contain B12.

B12 deficiency can cause quite a few neurological problems, including the ataxia you mentioned. Ataxia is a loss of muscular coordination. Peripheral neuropathy (loss of function in the nerves outside the spinal column) can occur. This will often cause numbness and abnormal sensations in the feet and legs. The spinal cord can be affected, causing weakness and ataxia, and loss of position sense, which greatly interferes with balance. The deficiency can also affect the cerebrum, the topmost level of the brain, and this is one of the recognized causes of dementia. Lack of B12 causes the individual nerves to deteriorate, and if not corrected, the nerves will die. Once this stage is reached even massive B12 therapy will not correct the problems, since there is no way at present to cause the nerves to regenerate once the cells have died. I doubt if your hearing problems are related to your B12 deficiency.

The anemia of B12 deficiency is similar to the anemia of folic acid deficiency, and in fact, taking large doses of folic acid will usually correct this anemia, although they will have no beneficial effect on the neurological problems. Therefore, someone taking folic acid regularly may have no anemia, but the neurological problems from the B12 deficiency will continue to progress. It is for this reason that many doctors opposed the recent legislation mandating folic acid supplements in milk. Although the reason for such supplements, the prevention of neural tube (brain and spinal cord) defects in the developing fetus is obviously desirable, the fear is that many more people will develop the neurological complications of B12 deficiency because they will not have the easily-diagnosed anemia.

I wonder if you have mistaken the dose of B12 that you are getting in your monthly injections. The standard B12 preparation for injection contains 1000 mcg/ml, and 1 ml is usually injected. To inject only 100 mcg would mean injecting only one tenth of 1 ml, a tiny amount which would be hard to draw up in the syringe accurately, unless you are using very small tuberculin syringes. If your anemia has been corrected since starting the B12, assuming you are not also taking folic acid, then you are getting an adequate dosage. The fact that your ataxia has not cleared may be due to the fact I mentioned above — that some of the nerves had already died before you started treatment. Larger doses will not improve the ataxia in that case.

There are now nasal forms of vitamin B12 that can be used once the anemia has been corrected by the injectable form. You might want to discuss one of these preparations with your doctor so that you can get away from the injections.

The information provided on Health Search Online is for educational purposes only and is not a substitute for medical advice, diagnosis or treatment.