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Scientific Studies

Vitamin B12 & health

Vitamin B12 & health


Vitamin B12 is required for proper red blood cell formation, neurological function, and DNA synthesis. In dietary supplements, vitamin B12 is usually present as cyanocobalamin , a form that the body readily converts to the active forms methylcobalamin and 5-deoxyadenosylcobalamin. Dietary supplements can also contain methylcobalamin and other forms of vitamin B12.

Vitamin B12 deficiency is characterized by megaloblastic anemia, fatigue, weakness, constipation, loss of appetite, and weight loss [1,3,27]. Neurological changes, such as numbness and tingling in the hands and feet, can also occur [5,28]. Additional symptoms of vitamin B12 deficiency include difficulty maintaining balance, depression, confusion, dementia, poor memory, and soreness of the mouth or tongue [29]. The neurological symptoms of vitamin B12 deficiency can occur without anemia, so early diagnosis and intervention is important to avoid irreversible damage [6].

Groups at Risk of Vitamin B12 Deficiency

Atrophic gastritis, a condition affecting 10%–30% of older adults, decreases secretion of hydrochloric acid in the stomach, resulting in decreased absorption of vitamin B12 [5,11,32-36]. Decreased hydrochloric acid levels might also increase the growth of normal intestinal bacteria that use vitamin B12, further reducing the amount of vitamin B12 available to the body [37].

Individuals with atrophic gastritis are unable to absorb the vitamin B12 that is naturally present in food. Most, however, can absorb the synthetic vitamin B12 added to dietary supplements. As a result, the IOM recommends that adults older than 50 years obtain most of their vitamin B12 from vitamin supplements [5]. However, some elderly patients with atrophic gastritis require doses much higher than the RDA to avoid subclinical deficiency [38].

Individuals with gastrointestinal disorders. Individuals with stomach and small intestine disorders, such as celiac disease and Crohn’s disease, may be unable to absorb enough vitamin B12 from food to maintain healthy body stores [12,23].


Strict vegetarians and vegans are at greater risk than lacto-ovo vegetarians and nonvegetarians of developing vitamin B12 deficiency because natural food sources of vitamin B12 are limited to animal foods [5].

Pregnant and lactating women who follow strict vegetarian diets and their infants

Vitamin B12 crosses the placenta during pregnancy and is present in breast milk. Exclusively breastfed infants of women who consume no animal products may have very limited reserves of vitamin B12 and can develop vitamin B12 deficiency within months of birth [5,43]. Undetected and untreated vitamin B12 deficiency in infants can result in severe and permanent neurological damage.

Interactions with Medications

Vitamin B12 has the potential to interact with certain medications. In addition, several types of medications might adversely affect vitamin B12 levels. A few examples are provided below :

Proton pump inhibitors

Proton pump inhibitors, such as omeprazole and lansoprazole , are used to treat gastroesophageal reflux disease and peptic ulcer disease. These drugs can interfere with vitamin B12 absorption from food by slowing the release of gastric acid into the stomach [83-85].

H2 receptor antagonists, used to treat peptic ulcer disease, include cimetidine , famotidine , and ranitidine . These medications can interfere with the absorption of vitamin B12 from food by slowing the release of hydrochloric acid into the stomach.


Metformin, a hypoglycemic agent used to treat diabetes, reduce the absorption of vitamin B12 [91-93], possibly through alterations in intestinal mobility, increased bacterial overgrowth, or alterations in the calcium-dependent uptake by ileal cells of the vitamin B12-intrinsic factor complex [92,93].

Vitalin and Vitalin Plus contain the optimal dose of vitamin B12 – actually the active form methylcobalamine, combined with folic acid –  the best option for metformin treated patients to maintain  the normal vitamin B12 level.