vitamin b12

Vitamin B12 is a water-soluble nutrient that, per the NIH Office of Dietary Supplements, supports healthy blood and nerve cells and is needed to make DNA. Adequate B12 also helps prevent megaloblastic anemia, a blood condition that can leave people feeling tired and weak. It is found naturally in animal foods (meat, fish, poultry, eggs, dairy), is added to some fortified foods such as breakfast cereals and nutritional yeast, and is sold as a dietary supplement (commonly the cyanocobalamin form) as well as by prescription as an injection or nasal gel.

The clearest established role is preventing and treating B12 deficiency and the megaloblastic anemia it causes. For other uses the NIH describes the evidence as limited or negative: although B12 taken with other B vitamins lowers blood homocysteine, research shows these vitamins do not reduce the risk of developing cardiovascular disease or stroke. Most studies show low blood B12 does not affect the risk of cognitive decline in older adults (with or without dementia), and more clinical trials are needed. Cancer findings are mixed and inconclusive. And the NIH states B12 does not provide energy, athletic, or endurance benefits in people who already get enough from their diet.

The NIH lists average daily recommended amounts in micrograms (mcg): 2.4 mcg for teens and adults, 2.6 mcg during pregnancy, and 2.8 mcg while breastfeeding (less for infants and children). Supplements often contain much higher doses, such as 500 or 1,000 mcg, of which the body absorbs only a small percentage; the NIH says these doses are considered safe and has not found any one form (cyanocobalamin, methylcobalamin, sublingual, etc.) to be better than another. Talk to your doctor, pharmacist, or dietitian before starting B12, especially if you suspect a deficiency, since true deficiency may need testing and prescription treatment such as injections.

According to the NIH consumer fact sheet, vitamin B12 has not been shown to cause any harm, even at high doses. Even so, persistent symptoms attributed to "low energy" or possible deficiency should be evaluated by a clinician rather than self-treated, because the NIH notes that untreated B12 deficiency can damage the nervous system, even in people without megaloblastic anemia. People who are pregnant, breastfeeding, or managing a medical condition should confirm their needs with a health care provider.

The NIH consumer fact sheet does not list specific adverse effects from supplemental vitamin B12 and states it has not been shown to cause harm even at high doses. The symptoms the fact sheet describes (tiredness, weakness, numbness or tingling, balance problems, memory issues) are signs of B12 deficiency, not side effects of taking the vitamin.

The NIH notes vitamin B12 can interact with certain medicines. Gastric acid inhibitors used for reflux and ulcers — including omeprazole (Prilosec), lansoprazole (Prevacid), cimetidine (Tagamet), and ranitidine (Zantac) — can interfere with absorption of B12 from food and may lead to deficiency. Metformin, used for prediabetes and diabetes, might reduce B12 absorption and lower blood levels. Tell your doctor and pharmacist about all supplements and medicines you take so they can check for interactions.