Special Report: Vitamin B12, How Much to Take and What Kind to Take.
What is the health risk of too little B12?
People who not get enough B12 may suffer from anemia, stroke, heart disease, muscular disorders, fatigue, nerve damage. Even with adequate consumption of cobalamin, a pre-cursor of the B12 co-enzyme, many people suffer B12 deficiency because of poor absorption, especially people over 50 and those on certain medications.
Young adults in a survey also showed inadequate B12 intake, but did not display symptoms, which may take many years to develop. Vegetarians are at greatest risk, especially pregnant and lactating women.
Ordinary vitamin tablets providing cobalamin may be ineffective in remedying deficiency because of absorption problems. High doses of folate may mask symptoms of B12 deficiency, but not remove the risk of nerve damage. B6 may also be deficient. Some people have difficulty in absorbing B6 and folate as well as B12 and may have to supplement with the co-enzymes instead of the precursors found in most vitamin tablets.
Dr. David J. Spence of the Stroke Prevention and Atherosclerosis Research Centre in Canada studied the effect of B vitamims on risk for stroke and heart disease, comparing the effect of low-dose versus high-dose vitamin therapy, they found that high-dose vitamin supplements reduced recurrent stroke, death and heart disease by 21 percent. Taking high doses of a B12 supplement reduced the risk of stroke and heart disease, the biggest reduction ocurring in those with poor ability to absorb B12 from food, Stroke, November 2005.
What is the health risk of too much B12?
The Institute of Medicine of the National Academy of Sciences did not establish a Tolerable Upper Intake Level for this vitamin because Vitamin B12 has a very low potential for toxicity. The Institute of Medicine states that "no adverse effects have been associated with excess vitamin B12 intake from food and supplements in healthy individuals". In fact, the Institute recommends that adults over 50 years of age get most of their vitamin B12 from vitamin supplements or fortified food because of the high incidence of impaired absorption of B12 from animal foods in this age group.
Reference: Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes: Thiamin, riboflavin, niacin, vitamin B6, folate, vitamin B12, pantothenic acid, biotin, and choline. National Academy Press. Washington, DC, 1998.
National Institute of Health: Factsheets
Read the complete report on B12.
- Most vitamin tablets that indicate B12 on the label contain cobalamin, an inactive analogue of B12. Cobalamin, whether in food or supplement form must be converted in the body to the active co-enzyme of B12. Unfortunately, some people cannot convert cobalamin. because of pathological conditions, genetic defects, digestive problems associated with age, or interactions with prescription drugs.
For example, as people age, secretion of pepsin declines and with it the ability to convert cobalamin into the active form of B12. Diuretics used to treat heart disease may leach B vitamins from the body. Prescription drugs used for gastric disorders may limit absorption of B12.
Two cobalamins are active as coenzymes in the human body: adenosylcobalamin and methylcobalamin. The body has the ability to convert at least some other cobalamins into one of these active forms.
Methylcobalamin is readily available as a supplement. Once every 15 days, I take one tablet containing 500 micro-gram (half a milligram). During the first week, I loaded with one tablet per day. If you eat red meat regularly you might skip the loading phase.
- The NORVIT study: "Researchers from Norway have found that treating patients who have had a heart attack with high doses of B vitamins [B6, B12, folic acid] does not lower the risk of getting another heart attack or stroke. Contrary to expectations, B vitamins may do more harm than good," Press release.
The surprising result of this large study is contrary to almost all other studies worldwide. Action on the basis of this trial should await confirmation from ongoing major trials in the USA and elsewhere.
One explanation for the unexpected outcome of NORVIT might be the following. The relatively isolated Norwegian population may differ genetically in ability to convert the inactive forms of the study vitamins into their active forms, the only forms the body can use. The NORVIT study used high doses of common vitamin tablets containing inactive forms of the vitamins and did not measure blood levels of the active form of the vitamins. Thus, NORVIT tells us nothing about effect of the active forms of the vitamins, the forms tested by sampling blood. Note: the inactive forms are: pyroxidine (B6), cobalamin (B12), folic acid (folate).
Because NORVIT was a controlled trial involving several participating hospitals, this critique would apply only if: the non-active forms of these vitamins interact adversely in some yet unknown way; adverse effects arise when repairing the deficiency of one of these vitamins while deficiency in another of the vitamins continues owing to malabsorption (a known hazard); or because of varying interactions with prescription drugs not controlled during the study; or because of varying dietary changes not controlled during the study.
DisclaimerThis information should not be substituted for the advice of a physician. Please consult with your family doctor before taking vitamins or food supplements.
Fred Colbourne It's never too late!
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