What is Vitamin B12?

Vitamin B12, a crucial member of the B vitamin family, plays a significant role in metabolic processes. The various forms of vitamin B12, known collectively as cobalamins, include methylcobalamin and 5-deoxyadenosylcobalamin. Being an essential vitamin, it cannot be synthesized by the body and must be obtained through dietary sources. Additionally, vitamin B12 is water-soluble, meaning it is not stored in the body and needs to be regularly consumed for optimal health.

Sources of Vitamin B12

Animal Products

Vitamin B12 is predominantly found in animal-based foods, including fish, meat, eggs, milk, and poultry.

Fortified Plant Foods

While natural plant foods typically lack vitamin B12, some are fortified with this essential nutrient. Examples include breakfast cereals, nutritional yeast, plant milks, and plant-based meat alternatives. It is important to check product labels to confirm that they are fortified with B12.

Supplementation Recommendations

Individuals who limit their intake of animal products, such as vegans and vegetarians, are often advised to consider vitamin B12 supplements. Supplemental forms, particularly cyanocobalamin, are commonly included in multivitamins and B complex vitamins.

Importance of Vitamin B12

Vitamin B12 is vital for several key bodily functions. It aids in the formation of red blood cells and DNA, which are essential for overall health. Furthermore, vitamin B12 supports the nervous system by maintaining the myelin sheath that surrounds neurons, enhancing their ability to communicate efficiently.

Enzymatic Functions

This vitamin is crucial for the activity of two important enzymes: methionine synthase and L-methylmalonyl-CoA mutase. Methionine synthase facilitates the conversion of homocysteine into the amino acid methionine, while L-methylmalonyl-CoA mutase transforms L-methylmalonyl-CoA into succinyl-CoA, aiding in the metabolism of fats and proteins.

Recommended Dietary Allowance (RDA)

The Recommended Dietary Allowance (RDA) for vitamin B12 is set at 2.4 mcg for adults, with pregnant and lactating women requiring slightly higher amounts of 2.6 mcg and 2.8 mcg, respectively.

Children’s RDA

For children, the RDA varies by age: 1.8 mcg for those aged nine to thirteen, 1.2 mcg for four to eight years old, 0.9 mcg for toddlers aged one to three, 0.5 mcg for infants aged seven to twelve months, and 0.4 mcg for infants under seven months. Vitamin B12 is passed through breast milk and is also added to infant formulas.

Meeting the RDA

According to the National Institutes of Health, the RDA represents the daily intake needed to meet the needs of 97-98 percent of healthy individuals. Foods such as three ounces of cooked sockeye salmon provide 200 percent of the RDA, and fortified nutritional yeast can meet 100 percent of the daily value for vitamin B12.

Upper Limits and Safety

Currently, there is no established upper limit (UL) for vitamin B12, as no adverse effects have been documented from excessive intake. Clinical trials have shown that high doses of vitamin B12, such as 0.4 mg for 40 months or 1.0 mg for five years, did not result in serious side effects.

Medication Interactions

Although vitamin B12 is considered safe, it may interact with certain medications, including proton pump inhibitors and H2 receptor antagonists. Therefore, it is advisable to inform your healthcare provider about any supplements you are taking.

Benefits of Vitamin B12

Cognitive Health

Some studies suggest that vitamin B12 supplementation may help protect against dementia in older adults, showing a correlation between low vitamin B12 levels and cognitive decline. However, evidence supporting the link between adequate B12 levels and reduced dementia risk remains inconclusive.

Cardiovascular Health

Vitamin B12 may also play a role in preventing cardiovascular disease, as low levels can lead to elevated homocysteine, a risk factor for heart conditions. Nevertheless, the American Heart Association states that there is insufficient evidence to confirm vitamin B12 as a preventive measure against cardiovascular disease.

Vitamin B12 Deficiency

At-Risk Populations

Certain individuals are at a higher risk for vitamin B12 deficiency. Vegetarians and vegans should monitor their B12 levels and consider supplementation, particularly pregnant and lactating women on plant-based diets due to their increased requirements.

Absorption Issues

Some individuals may have difficulty absorbing vitamin B12, increasing their risk of deficiency. This includes older adults and those with conditions such as pernicious anemia or gastrointestinal disorders like Crohn’s disease or celiac disease.

Symptoms of Deficiency

Vitamin B12 deficiency can lead to various symptoms, including fatigue, weakness, appetite loss, weight loss, constipation, and numbness in extremities. Neurological symptoms may also occur, such as poor memory, confusion, or depression. If left untreated, deficiency can result in severe nervous system damage, highlighting the importance of early detection.

Treatment and Supplementation

Vitamin B12 deficiency is typically treated with intramuscular B12 injections, particularly for those who cannot absorb it through digestion. In some cases, high-dose oral supplements may be effective. Adequate intake can also be achieved through dietary sources or supplements.

Consultation with Healthcare Providers

If you suspect a vitamin B12 deficiency or are at increased risk, consider getting your blood levels tested. Always consult with your doctor before starting any new vitamin or mineral supplement to ensure they do not pose risks related to your medications or health conditions.

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/