Harm in B12 supplementation?


Kathy Pollard, MS


Any harm in supplementing with 5000mcg of B12 daily?


No harm, just expensive urine. Since vitamin B12, or cobalamin, is water-soluble vitamin and excess will be excreted out, there is no risk of toxicity and no upper limits established, but neither is there any benefit from large doses.1

The bodys ability to absorb B12 from supplements is limited by its capacity to produce intrinsic factor, a glycoprotein which binds to the vitamin in the upper intestine
to usher it into intestinal cells. For most healthy people roughly 10 mcg of a 500 mcg oral supplement can actually be absorbed, so there is no benefit to taking a higher dose.2

Though we are able to store some B12 in our bodies for up to three years, we are finding that many people can become deficient more quickly, and since this vitamin is not found in our sterile, modern food supply, supplementation is often appropriate. But very small amounts ovitamin B-12 are needed daily. The RDA is 2.micrograms (mcg) per day for adults, 2.6 mcg for pregnant females, and 2.8 mcg for lactating females. Vitamin absorption does decrease with age and those over 50 years are advised to supplement. Keep in mind that many foods are fortified with this vitamin, including soy products, plant milks, cereal products, meat analogs and nutritional yeast.

Vitamin B12 is such a vital nutrient for many systems in our body, including energy production, red blood cell formation, and both DNA and fatty acid synthesis, that this vitamin is worth consideration. Since our food comes from soil bereft of the bacteria that produces this vitamin, we take in less than our body expects. Deficiency is associated with increased risk for neurological, cardiovascular and cognitive, dysfunction, as well as megaloblastic anemia. Though animal foods offer vitamin B12, it may not be the best source to rely on, as with them come cholesterol, excess fat and animal protein. Supplementation appears to be most effective.Further, understand that vitamin B12 works with many other nutrients to provide proper function, particularly folate (vitamin B9), and though we do find lower levels of vitamin B12 in vegans, plant-based diets offer all of the other vitamins and minerals needed.4

Also note that though B12 supplementation is considered nontoxic, some medications may interact with B12 supplementation.5


  1. Gropper SS, Smith JL & Groff JLAdvanced Nutrition and Human Metabolism, 5th edition. Belmont, CA. Pp. 359-363
  2. Carmel R. How I treat cobalamin (vitamin B12) deficiency. Blood.2008;112:2214-21.
  3. Tucker, K. L., Rich, S., Rosenberg, I., Jacques, P., Dallal, G., Wilson, P. W., & Selhub, J. (2000). Plasma vitamin B-12 concentrations relate to intake source in the Framingham Offspring study. Am J Clin Nutr, 71(2).
  4. Woo, K. S., Kwok, T. C., & Celermajer, D. S. (2014). Vegan diet, subnormal vitamin B-12 status and cardiovascular health. Nutrients, 6(8), 3259-3273. doi:10.3390/nu6083259
  5. National Institutes of Healthy Dietary Supplement Fact Sheet. https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/