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Providing perspectives on recent research into vitamins and nutritionals


Using the Tolerable Upper Limit to Avoid Excessive Vitamin Supplementation

By Julia Bird

Vitamins are essential: there is absolutely no doubt about that. However, as with everything, moderation is the best strategy. While it is important to avoid too little, too much is also a problem, as was found recently in a case study of vitamin B6 intoxication, described by Cupa and co-workers. A woman was admitted to hospital with vomiting and diarrhea, and an increasingly brown colored skin. She had had bariatric surgery 10 months earlier. Bariatric surgery patients can be at risk of various vitamin and mineral deficiency as the surgery necessarily involves reducing the size of parts of the digestive system, as discussed by Alvarez-Leite, and supplementation can be prudent to avoid deficiency. The patient had been taking various vitamin and mineral supplements on the advice of her doctor. The daily doses were considerably higher than the RDA: 300 mg vitamin B1 (300 times the RDA), 20 mg vitamin B2 (20 times the RDA), 300 mg vitamin B6 (200 times the RDA), 1000 μg vitamin B12 per 3 months intramuscularly (400 times the oral RDA), 20,000 IU vitamin D per week (3 times the RDA), 93 mg iron (10 times the RDA) and 2550 µg folic acid (6 times the RDA). For vitamins B6, iron and folate, the amounts were higher than the “Tolerable Upper Limit”. This limit reflects the maximum amount that can be taken over the long term that will pose no risk of adverse health effects for almost all individuals in the population. There has been no Tolerable Upper Limit developed for vitamins B1, B2 and B12.

High doses in the short term may be justified in order to bring deficient levels into the normal range. The patient in the case study had her vitamin levels measured as part of a range of tests. It turned out that the concentrations of the active form of vitamin B6 in her blood were exceedingly high, over 20 times higher than the maximum of the normal range. Vitamin B6 is also used to treat various conditions such as carpal tunnel syndrome, seizures and sickle cell disease. While sensory neuropathy and loss of control of body movements are classic side effects according to the Office of Dietary Supplements, sensitivity to light and gastrointestinal symptoms are also found with high doses. If large doses are taken over the long term, patients should be warned about possible side effects and monitored for excessive levels.

The patient stopped taking the vitamin B6 supplements immediately, and 5 months later her blood levels had returned to normal. The gastrointestinal complaints stopped and her skin lightened over time. The other micronutrient supplementation was continued, although vitamin B1 dosing was reduced by two thirds.

Tolerable Upper Limits for vitamins and minerals are provided for a reason: to prevent negative health effects from excessive intakes. People who deliberately exceed the Tolerable Upper Limit should do so under the careful supervision of a doctor, and be alert for the known side effects. It is also important to avoid intakes of vitamin B6 that are too low. Vitamin B6 deficiency is surprisingly common. For example, around 10% of the US population is deficient in vitamin B6, according to the CDC. In addition, data from the Micronutrient Calculator show that about 12% of the population aged over 2 years does not meet the EAR for vitamin B6. Like with anything that we ingest, too little is a problem. So is too much. If you are taking high doses, check the Tolerable Upper Limit, and be wary. Vitamin B6 is no different. Get the right amount to protect your health.


Main article:

Cupa N, Schulte DM, Ahrens M, Schreiber S, Laudes M. Vitamin B6 intoxication after inappropriate supplementation with micronutrients following bariatric surgery. European Journal of Clinical Nutrition (2015) 69, 862–863; doi:10.1038/ejcn.2015.83; published online 3 June 2015


Supporting citations:

Alvarez-Leite JI. Nutrient deficiencies secondary to bariatric surgery. Curr Opin Clin Nutr Metab Care. 2004 Sep;7(5):569-75.

Centers for Disease Control and Prevention. Second National Report on Biochemical Indicators of Diet and Nutrition in the U.S. Population; 2012.

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