Food is medicine: The science behind vitamin B12

Key takeaways:

• Vitamin B12 supplements may offer neurological benefits for those who are deficient.
• Some researchers have studied its supplementation for other benefits, like sleep, but the evidence is uncertain.

Vitamin B12 supplementation may be helpful for those with deficiencies, according to an expert, but evidence among the general population is inconclusive.

Vitamin B12 is necessary for DNA synthesis, healthy red blood cell formation and the function, myelination and development of the central nervous system, Carol J. Haggans, MS, RD, scientific and health communications consultant the NIH Office of Dietary Supplements, told Healio.

“Vitamin B12 is found only in animal products, including fish, meat, poultry, eggs and dairy products,” Haggans said. “Therefore, people who follow vegan diets need to obtain vitamin B12 from either fortified foods, such as many breakfast cereals and fortified nutritional yeasts, or dietary supplements.”

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For men and most women, the recommended dietary allowance (RDA) of vitamin B12 is 2.4 µg per day. During pregnancy, that increases to 2.6 µg per day, and during lactation, it increases again to 2.8 µg per day.

“Vitamin B12 supplementation is used mainly to correct vitamin B12 deficiency which can cause megaloblastic anemia and neurological changes such as numbness and tingling in the hands and feet,” Haggans said. “In addition, vitamin B12 deficiency affects people with pernicious anemia. Pernicious anemia is an autoimmune disease that causes a lack of intrinsic factor, resulting in malabsorption of vitamin B12 and thus, vitamin B12 deficiency. People with pernicious anemia are often treated with intramuscular vitamin B12 injections to bypass any barriers to absorption of oral vitamin B12.”

Patients who follow vegan diets are older, have had surgery or have disorders more likely to be deficient than others, Haggans said.

“Many older adults, especially those with atrophic gastritis, have trouble absorbing vitamin B12, so people 50 should get most of their vitamin B12 from fortified foods and/or dietary supplements,” Haggans said. “These forms are more easily absorbed than the vitamin B12 in food.”

Summary of evidence

Evidence on the benefits of vitamin B12 supplementation is largely mixed.

In 2020, a review of 35 studies revealed no evidence showing positive effects of vitamin B12 on depressive symptoms. However, researchers wrote that lower levels of vitamin B12 in the body were linked to a higher risk for developing depression, and therefore concluded that early vitamin B12 supplementation can delay depression onset improve the effect ofantidepressants.

Other research is less clear.

A 2021 systematic review, meta-analysis and meta-regression of 16 randomized controlled trials also found no evidence that vitamin B12 supplements had any effect on cognitive function outcomes or measures of depression for patients without advanced neurological disorders.

Additionally, a 2023 community-based, double-blind, randomized, placebo-controlled trial in Nepal found that supplementation improved vitamin B12 status, but it had no effect on infant neurodevelopment and growth. The researchers therefore concluded that there is no evidence to support routine vitamin B12 supplementation during pregnancy.

Also, a 2021 randomized controlled trial in Nepal that included 600 infants evaluated vitamin B12 supplementation’s impact on sleep. The researchers found that, for infants and other high-risk subgroups, vitamin B12 supplementation did not impact sleep; it had no effect on total sleep duration, wake after sleep onset or sleep duration at night.

More information

Unlike some other supplements, Haggans said there is no tolerable upper intake level for vitamin B12, “so it is considered safe at any dose.”

“Vitamin B12 is bound to protein in food and must be released by the action of hydrochloric acid and gastric protease in the stomach before it can be absorbed,” Haggans said. “Vitamin B12 then combines with intrinsic factor, a transport and delivery binding protein, and the resulting complex is absorbed in the small intestine. Disruptions in this process can result in vitamin B12 deficiency even in the presence of sufficient intakes.”

The Office of Dietary Supplements offers resources for health care providers and consumers. To learn more about vitamin B12 and other supplements, check out the Office of Dietary Supplements Fact Sheets.

Editor’s Note: Healio is highlighting the clinical value of various supplements. See other installments of the series here:

• Melatonin
• Omega-3
• Zinc and other supplements for immune function
• Vitamin D
• Calcium
• Ashwagandha
• Magnesium
• Folic acid
• Iodine

References:

• Chandyo RK, et al. Lancet. 2023;doi:10.1016/S0140-6736(23)00346-X.
• Hysing M, et al. Clin Nutr. 2022;doi:10.1016/j.clnu.2021.11.040.
• Markun S, et al. Nutrients. 2021;doi:10.3390/nu13030923.
• Sangle P, et al. Creus. 2020;doi:10.7759/cureus.11169.