Dear Doctor: I’m 19 years old, and I switched to a vegan diet six months ago. I’m careful about getting enough vitamin B12. However, some of my girlfriends say it’s not that important and your body makes all the B12 you need. Is that true?

Dear Reader: This is a serious issue, and the answer is that nothing your friends are telling you about vitamin B12 is correct. In fact, their advice puts you and any vegans who heed it in real danger. First, vitamin B12 is vital to good health. (More about that in a moment.) And no, your body does not manufacture it. That makes it imperative for everyone following a plant-based diet to make getting adequate B12 a priority.

For those not familiar with the specifics, a vegan diet excludes all animal-based food. That means no meat, fish, seafood, dairy products and eggs. The restrictions also cover honey, which comes from bees, and gelatin, a protein obtained from the bones and connective tissue of animals, often cows or pigs. Because B12 is naturally available only in the major animal products that vegans don’t eat, getting enough becomes a daily goal.

So what is B12 exactly? It’s the most complex of the 12 B vitamins, and it is categorized as an essential vitamin. That means the body requires it, but doesn’t make it. Instead, B12 is produced by certain bacteria that flourish in the gut microbiomes of animals. The B12 they make gets distributed throughout the animal’s body, where it binds to proteins. When you eat an egg, drink some milk or have a burger, the process of digestion releases the B12 from the animal protein and makes it available for your body to use.

A B12 deficiency can result in chronic weakness; mental issues such as poor thinking, confusion or depression; heart palpitations; vision loss; exhaustion; pain and tingling in the extremities; loss of balance; muscle weakness; or difficulty walking. And it’s not just vegans who are at risk. If you’re not sure about your B12 status, your health care provider can check your levels with a simple blood test.

Eve Glazier, M.D., MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and assistant professor of medicine at UCLA Health.

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