vitamin B12

What is vitamin B12?

Vitamin B12 is one of the B vitamins that are primarily involved in metabolism.  Different types of vitamin B12 are referred to as cobalamins, and the forms of B12 seen in humans are methylcobalamin and 5-deoxyadenosylcobalamin.  It is an essential vitamin, which means that it is not synthesized in the body and it must be obtained through the diet.  It is also a water-soluble vitamin, which means that it is not readily stored in the body and it must be consumed on a regular basis to ensure optimal health.

Where is vitamin B12 found?

Vitamin B12 is found in animal products such as fish, meat, eggs, milk, and poultry.  Vitamin B12 is not usually seen in plant foods, but some plant foods are fortified including breakfast cereals, nutritional yeast, plant milks, and plant-based mock meat products.  Make sure you check the label to ensure these products are actually fortified with B12. 

Since vitamin B12 is not found in significant amounts in plant-based foods naturally, it is often recommended for people who limit their intake of animal products, such as vegans and vegetarians, to take a vitamin B12 supplement.  Supplemental vitamin B12, or cyanocobalamin, is often added to multivitamins, multi-B complex vitamins, and supplements containing only vitamin B12.

Why is it important?

Vitamin B12 is important because it helps carry out many vital functions in the body.  Firstly, it helps form red blood cells and DNA, which are both essential. 

Vitamin B12 is thought to help the nervous system by maintaining the myelin sheath around neurons (nerve cells).  Myelin surrounds the neurons and insulates them, allowing neurons to communicate more quickly and effectively. 

Vitamin B12 is essential to the function of two different enzymes: methionine synthase and L-methylmalonyl-CoA mutase.  Methionine synthase helps convert homocysteine to the amino acid methionine.  L-methylmalonyl-CoA mutase helps convert L-methylmalonyl-CoA to succinyl-CoA, which helps metabolize fats and proteins.

What is the RDA for vitamin B12?

The Recommended Dietary Allowance (RDA) for vitamin B12 is 2.4mcg for men and women, and 2.6mcg and 2.8mcg for pregnant and lactating women, respectively.

The RDA is 1.8mcg for children between nine and thirteen years of age, 1.2mcg for children between four and eight years of age, 0.9mcg for toddlers between one and three years, 0.5mcg for infants between seven and twelve months, and 0.4mcg for infants under seven months of age.  Vitamin B12 is transmitted through breast milk, and it is also added to infant formulas.

These values are given by the National Institutes of Health, and the RDA represents the daily intake that is sufficient to meet the needs of 97-98 percent of healthy individuals.  The RDA for vitamin B12 can be met through food or supplements; three ounces of cooked sockeye salmon contains 200 percent of the RDA, and one serving of nutritional yeast fortified with 100% of the daily value for vitamin B12 contains 100 percent of the RDA.

How much is too much?

The upper limit (UL) for vitamin B12 is not established, as there are no recorded adverse effects from taking too much vitamin B12.  In fact, in two different clinical trials, vitamin B12 supplementation at doses of 0.4 mg for 40 months and 1.0mg for five years did not result in any serious side effects. 

The Upper Limit (UL) represents the maximum daily intake of a vitamin or mineral that is unlikely to cause negative health effects.  Although there is no recorded toxicity from excess vitamin B12, it has the potential to interfere with certain medications, including proton pump inhibitors and H2 receptor antagonists.  To help prevent this, it is important that you tell your doctor and pharmacist about any supplements you may be taking.

What are the benefits of vitamin B12?

Some researchers hypothesized that vitamin B12 supplementation could potentially help protect against dementia in older adults.  This was supported by the fact that one study found a positive relationship between low vitamin B12 levels and cognitive decline.  However, there is insufficient evidence to support that adequate B12 levels are associated with lower levels of dementia, and so this is inconclusive.

Vitamin B12 was also believed to potentially help prevent cardiovascular disease, as low levels of vitamin B12 can result in elevated homocysteine levels.  Elevated homocysteine levels are a risk factor for cardiovascular disease.  However, there is not enough evidence to support vitamin B12 as a preventative measure against cardiovascular disease according to the American Heart Association.

Vitamin B12 deficiency

Some people have a higher risk of vitamin B12 deficiency than others.  Firstly, people following a vegetarian or vegan diet should watch their vitamin B12 levels and consider incorporating a supplement because plant foods generally do not naturally contain vitamin B12.  This risk is amplified in pregnant and lactating women following plant-based diets because they have higher B12 requirements.

Some people absorb less vitamin B12 than average, which can put them at an increased risk of deficiency.  Some groups include older adults, people with pernicious anemia, or gastrointestinal disorders such as Crohn’s disease or celiac disease.

Vitamin B12 deficiency can result in many symptoms, including fatigue, weakness, appetite and weight loss, constipation, numbness of the extremities, and megaloblastic anemia.  Some people may experience neurological symptoms such as poor memory, dementia, confusion, or depression.  If this is not treated, it could potentially result in damage to the nervous system, so early detection is important.

Vitamin B12 supplementation

Vitamin B12 is usually treated by intramuscular B12 injections because these can work for people who do not absorb vitamin B12 through their digestive system.  However, in some cases, high-dose oral vitamin B12 supplements work well also.  This deficiency can also be prevented by taking vitamin B12 supplements or meeting your nutritional needs through the diet. 

If you think you have a vitamin B12 deficiency or are at an increased risk, consider getting your blood levels tested.  As always, consult your doctor before you begin taking any vitamin or mineral supplement, to make sure your medications or health conditions don’t make it a serious risk.

References:

Clarke, R., Birks, J., Nexo, E., Ueland, P. M., Schneede, J., Scott, J., . . . Evans, J. G. (2007). Low vitamin B-12 status and risk of cognitive decline in older adults. The American Journal of Clinical Nutrition, 86(5), 1384-1391. doi:10.1093/ajcn/86.5.1384

Leishear, K., Boudreau, R. M., Studenski, S. A., Ferrucci, L., Rosano, C., Rekeneire, N., . . . Strotmeyer, E. S. (2012). Relationship Between Vitamin B12 and Sensory and Motor Peripheral Nerve Function in Older Adults. Journal of the American Geriatrics Society, 60(6), 1057-1063. doi:10.1111/j.1532-5415.2012.03998.x

Lichtenstein, A. H., Appel, L. J., Brands, M., Carnethon, M., Daniels, S., Franch, H. A., . . . Wylie-Rosett, J. (2006). Diet and Lifestyle Recommendations Revision 2006. Circulation, 114(1), 82-96. doi:10.1161/circulationaha.106.176158

Lonn, E., Yusuf, S., Arnold, M. J., et al (2006). Homocysteine lowering with folic acid and B vitamins in vascular disease. N Engl J Med, 354(15), 1567-1577. doi:10.1056/NEJMoa060900

Office of Dietary Supplements – Vitamin B12. (2020, March 30). Retrieved September 02, 2020, from https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/

Skerrett, P. (2019, February 11). Vitamin B12 deficiency can be sneaky, harmful. Retrieved September 02, 2020, from https://www.health.harvard.edu/blog/vitamin-b12-deficiency-can-be-sneaky-harmful-201301105780

Vitamin B12. (2019, June 04). Retrieved September 02, 2020, from https://www.hsph.harvard.edu/nutritionsource/vitamin-b12/

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