Vitamin B12 is one of eight B vitamins needed for a range of important physiological functions. It’s found naturally in animal products and fortified foods, or can be taken via supplement form or administered via injection.

“Vitamin B12 is crucial to the human body, which needs it to produce new DNA, red blood cells, proteins, hormones and fats,” explains Heather Mangieri, a registered dietitian nutritionist. “Vitamin B12 is also key to the health of nerves. It’s part of the vitamin B complex, which includes thiamin, niacin, vitamin B6 and folate. Each of these vitamins has its own unique role in the body, but most B vitamins have a role in helping your body's cells produce energy.”

The typical American diet meets or exceeds the daily recommended amount of vitamin B12 (2.4 micrograms). However, vitamin B12 deficiency remains a common problem in the United States because it can be affected by other factors, like age and digestion. Older adults, those on a vegan diet and pregnant women are especially prone to being deficient.

What’s more, people may not realize that vitamin B12 is missing from their diets because the liver can store a five-year supply in reserve. Without treatment, a deficiency can lead to mood swings or depressive symptoms, fatigue, gastric problems, muscle weakness, nerve damage and anemia.

In this article we’ll dive into the benefits of B12, as well as common sources to add to your diet, and signs of deficiency.

Why do we need vitamin B12?

Vitamin B12 has many roles in the body:

Making red blood cellsKeeps the nervous system healthyReleases energy from foodDNA synthesisHelps the body use folateSupports a healthy pregnancyImportant for prevention of brain and spinal cord birth defectsRegulates mood (B12 is needed to produce the feel-good chemical serotonin)

How much vitamin B12 should you consume?

The recommended daily intake (RDI) of vitamin B12 for American adults is 2.4 mcg a day, according to the National Institutes of Health (NIH) guidelines. Pregnant and breastfeeding women will need slightly more. Only animal foods contain B12 naturally, so if you’re vegan or vegetarian, you will need to take a supplement to up your intake or eat fortified foods.

Most Americans get enough of the vitamin from food, but some have trouble absorbing B12. The body absorbs vitamin B12 from food in a two-step process:

1. Hydrochloric acid in the stomach separates B12 from the protein it is attached to.

2. The vitamin B12 then combines with a glycoprotein made by the stomach, called gastric intrinsic factor, and the body absorbs them together.

The process is slightly different when it comes to B12 supplements, as they aren’t attached to protein and bypass the first step. But even B12 in supplement form needs to combine with intrinsic factor in the stomach to be absorbed by the body.

People who suffer from the autoimmune disease pernicious anemia can’t make intrinsic factor, so they have difficulty absorbing B12 from both food and dietary supplements.

The best sources of vitamin B12

BeefLiverKidneysMilkCheeseYogurtEggsFortified breakfast cerealsTunaSalmonShellfishSome fortified mushroomsMarmitePlant-based milks

Symptoms of vitamin B12 deficiency

If you have a B12 deficiency you could experience a wide range of symptoms, including weight loss, lack of appetite, fatigue, depression, poor memory and difficulty thinking straight. You could also experience a numb feeling in the hands and feet, loss of balance, sore mouth or tongue and constipation. Yellow skin, anemia, paranoia and hallucinations could indicate a vitamin B12 deficiency, according to Harvard Health Publications.

Talk to your doctor rather than self-medicating with supplements as many of the symptoms can be signs of another condition, says Mangieri.