Vitamin B12 is crucial to the human body, which needs it to produce new DNA, red blood cells, proteins, hormones and lipids (fats). Vitamin B12 is also key to the health of nerves.
Vitamin B12 is part of the vitamin B complex, which includes thiamin, niacin, vitamin B6, folate and vitamin B12. 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 to produce energy," said Heather Mangieri, a spokeswoman for the Academy of Nutrition and Dietetics and owner of Nutrition Checkup in Pittsburgh.
The typical American diet meets or exceeds the daily recommended amount of vitamin B12. However, vitamin B12 deficiency remains a common problem in the United States because it can be affected by other factors, like age and digestion. Seniors, vegans and pregnant women are especially prone to vitamin B12 deficiency. People may not realize vitamin B12 is missing from their diets because the liver can store a 5-year supply in reserve.
Symptoms of vitamin B12 deficiency
A vitamin B12 deficiency has a wide range of symptoms. Someone with low vitamin B12 may lose their appetite, lose weight or feel tired and weak. Depression, poor memory and trouble thinking can all be symptoms of a vitamin B12 deficiency. Other symptoms of a vitamin B12 deficiency include a numb or tingling feeling in the hands and feet, a loss of balance, a sore mouth or tongue and constipation. Yellowed skin, anemia, paranoia and hallucinations may also indicate a vitamin B12 deficiency, according to Harvard Health Publications.
If you notice any of these symptoms, you should consult a health care professional, rather than trying to self-treat with supplements, experts say.
"People shouldn't jump to supplements if they have these symptoms," said Vandana Sheth, a registered dietitian nutritionist and spokeswoman for the Academy of Nutrition and Dietetics. Many of these symptoms can be signs of another condition, Sheth said, adding that blood tests can confirm a deficiency, and a diet assessment may help people get their needed nutrients without resorting to supplements.
Age and digestive problems can cause a vitamin B12 deficiency, even if a person gets plenty of vitamin B12 from food. Nearly one-third of people over age 50 suffer from atrophic gastritis, a thinning of the stomach lining that interferes with vitamin B12 absorption. The U.S. Centers for Disease Control and Prevention estimates that 3.2 percent of adults over age 50 are deficient in vitamin B12. Another 20 percent of adults may have borderline deficient levels of vitamin B12. In fact, the CDC recommends "all people 51 years of age and older should get most of their daily vitamin B12 through supplements containing vitamin B12 or foods fortified with vitamin B12."
Pregnancy can also lower vitamin B12 levels, as can hyperthyroidism (overactive thyroid) if it causes the person to produce too much body heat, according to the NIH. Pregnant or breastfeeding women who do not get enough vitamin B12 may cause their babies to have low vitamin B12 levels.
Low levels of stomach acid can also lead to overgrowth of bacteria in the small intestine. These bacteria, in turn, leach vitamin B12 from the body.
What vitamin B12 supplement makers say
Supplement makers market vitamin B12 as an energy and endurance booster, particularly for athletes. People also take vitamin B12 to improve their mood and concentration as well as their immune system.
Vitamin B12 supplements are purported to reduce the risk of breast cancer, lung cancer and cervical cancer. Vitamin B12 supplements are also said to protect against the poisons in tobacco smoke. Some people use vitamin B12 supplements to help treat male infertility, sleep disorders, depression, inflammatory bowel disease, asthma, multiple sclerosis, allergies and the skin condition vitiligo.
Vitamin B12 supplements are frequently touted to prevent osteoporosis, diabetes, cardiovascular disease and stroke. Vitamin B12 is also said to help some sleep disorders, some mental disorders and slow the progression of dementia in the elderly.
Supplement makers also say vitamin B12 supplements can help treat conditions such as Lyme disease, gum disease, some skin infections, liver disease and kidney disease. Combining avocado oil and vitamin B12 in a topical treatment can supposedly improve psoriasis or eczema symptoms, and vitamin B12 is also said to help reduce ringing in the ears and swollen tendons.
Do vitamin B12 supplements work?
Vitamin B12 supplements can treat a deficiency, but dietitians recommend getting your vitamin B12 from food, if possible, before trying a supplement. Many meat and dairy products have vitamin B12. Clams, crab, beef liver and many fish are particularly high in vitamin B12. Eliminating meat, dairy and fortified cereals from your diet may require you to supplement vitamin B12, Sheth said.
"In general, vitamin B12 is found in animal products," Sheth said, so, strict vegetarians and vegans must actively seek out another source of the vitamin. In people who are making the transition to a vegan diet, a vitamin B12 deficiency may not show up for a while, Sheth said.
Nutritional yeast is the best vegetarian source of vitamin B12, Sheth said. Just 2 teaspoons (6 grams) a day of nutritional yeast should cover an adult's vitamin B12 needs. Additionally, most multivitamins contain the daily recommended amount of vitamin B12, and fortified cereals typically provide ample vitamin B12.
Other strict diets may unintentionally cut vitamin B12. "A lot of people have cut grains, and a lot of B vitamins are fortified in our grain products," Mangieri said. "If you're going to eliminate something from your diet, investigate what you have eliminated and where else you can get those nutrients. You have to really work with a registered dietitian or do your homework."
The average adult should get 2.4 micrograms of vitamin B12 per day. Women who are pregnant or breastfeeding need more — about 2.8 micrograms a day, according to recommendations from the National Institutes of Health's Office of Dietary Supplements.
When vitamin B12 pills don't help
The body requires both stomach acid and a protein made in the stomach, called intrinsic factor, to digest vitamin B12. First, stomach acid breaks off a protein that comes attached to vitamin B12. Then, the intrinsic factor is attached to the vitamin B12 molecule. Once in this form, vitamin B12 can be used in cells throughout the body. A problem with either stomach acid or intrinsic factor can lead to a vitamin B12 deficiency.
Oral vitamin B12 supplements contain a form of vitamin B12 that is easy to absorb without stomach acid, but these pills may not treat all causes of vitamin B12 deficiency. People who have undergone gastric bypass surgery, for example, can develop a deficiency in the intrinsic factor.
"They could be taking all the B12 orally that they want, and they won't be absorbing it properly," Mangieri said.
Some autoimmune conditions, such as pernicious anemia, attack and destroy intrinsic factor, according to the NIH's Office of Dietary Supplements. People with celiac disease or Crohn's disease may also have difficulty absorbing the vitamin B12 from food or vitamin supplements.
A Schilling test can determine if a person is absorbing vitamin B12 properly. Doctors may prescribe vitamin B12 injections to treat people who have a deficiency but would not benefit from vitamin B12 pills. Vitamin B12 can also be administered in a nasal gel, according to the NIH's Office of Dietary Supplements.
Does extra vitamin B12 boost health?
Thanks to its association with the amino acid homocysteine, vitamin B12 is touted for its supposed ability to help several conditions. Someone with low vitamin B12 levels typically has high levels of homocysteine in the blood. High levels of homocysteine are commonly found in people with osteoporosis, dementia, heart disease, cognitive impairment and depression.
Studies have shown a combination of vitamin B12, folic acid and vitamin B6 can lower homocysteine levels. However, research has not confirmed that using vitamins to lower homocysteine levels actually treats or prevents health problems.
For example, one study of 5,522 people with vascular disease showed a vitamin B supplement did not reduce the risk of dying from heart attack. Researchers assigned some volunteers to a placebo and others to a combination of folic acid, vitamin B6 and vitamin B12 supplement. Vitamins reduced homocysteine levels in the study participants, but the placebo group and the group taking vitamins had a similar risk of dying from major cardiovascular events during the five-year study, according to the paper, published in August 2006 in the New England Journal of Medicine.
Vitamin B12 supplements most likely won't reduce your risk for heart disease, according to the NIH's Office of Dietary Supplements. It's still unknown whether vitamin B12 supplements have an effect on diabetes, high cholesterol or preventing arteries from reclogging after a stent procedure, according to the U.S. National Library of Medicine.
A few preliminary studies — some that provided supplements and some that simply recorded vitamin B12 levels in people over time — have found a weak link between vitamin B12 supplements and a reduced risk of osteoporosis. However, more studies are needed to see if vitamin B12 could help reduce osteoporosis risk, according to the Linus Pauling Institute at Oregon State University.
Some preliminary studies have found a weak link between vitamin B12 and a reduced cancer risk, but the connection is still unclear. One study compared blood samples and diet questionnaires of 712 breast cancer patients and 712 women without breast cancer. Diet questionnaires (taken from 1980 through 1990) and blood samples (taken in 1990) showed that higher levels of vitamin B12 were associated with a lower risk of breast cancer, but only among women who had not yet hit menopause. Levels of folate and vitamin B6 had a stronger link to breast cancer risk in the study, according to the March 2003 paper, published in the Journal of the National Cancer Institute.
Preliminary evidence has not found that vitamin B12 blood levels affect lung cancer, according to the National Library of Medicine, but combining folic acid, thiamine, riboflavin and vitamin B12 may help prevent cervical cancer.
Low levels of vitamin B12 are commonly linked to health problems, but recent research found that having abnormally high levels of vitamin B12 in the blood may indicate a cancer risk. Researchers examined lab tests and cancer diagnoses of more than 300,000 patients in a Danish medical registry from 1998 to 2010. Only 6 percent of the people in the study had vitamin B12 levels higher than the recommended upper limit, and these people had a higher risk of being diagnosed with cancer within one year of their abnormal blood tests, especially a cancer related to smoking (lung cancer) or alcohol, according to the December 2013 paper, published in the Journal of the National Cancer Institute.
It is not likely that vitamin B12 is an effective treatment for sleep disorders in seniors — at least when it's used in combination with vitamin B6 and folic acid, according to the National Library of Medicine.
Low vitamin B12 levels are commonly found with other physical signs of mental decline, such as high homocysteine levels or low folate levels. And people diagnosed with Alzheimer's disease and dementia often have low vitamin B12 levels. However, studies have not conclusively shown that vitamin B12 supplements will improve memory or thinking skills in the elderly, in Alzheimer's patients, in dementia patients or among stroke survivors. The NIH's Office of Dietary Supplements says that more large clinical trials are needed to prove whether vitamin B12 can influence cognitive function and the risk of developing dementia.
A study published in 2014 in the journal Neurology, which included nearly 3,000 older adults, found that taking a combination of vitamin B12 and folic acid (another type of B vitamin) didn't improve people's performances on thinking and memory tests.
More studies are needed to determine whether vitamin B12 supplements can improve depression symptoms. Preliminary evidence suggests that depressed people respond better to treatment if they have healthy levels of vitamin B12. Researchers in Finland took blood samples from 115 patients diagnosed with major depression disorder. The patients underwent six months of treatment, including therapy and medication, before giving another blood sample. Those with higher levels of vitamin B12 at the start and end of the study were more likely to "fully" respond to treatment, according to the study, published in December 2003 in the online journal BMC Psychiatry. Researchers considered 40 people in the study to have a "full response" to depression treatment, 34 had a partial response and 41 people had no response.
Yet other preliminary studies have failed to show that vitamin B12 supplements alone can help depression. A two-year study of 909 elderly people examined whether groups assigned to exercise, mental health education or vitamin supplements had fewer depression systems. In the study, folic acid and vitamin B12 supplements did not change depression symptoms any more than a placebo did. Four follow-up surveys over the span of two years found that only mental-health education changed depression symptoms, according to the July 2012 paper in the British Journal of Psychiatry.
Vitamin B12 will not enhance athletic performance or increase energy levels in people who are not deficient in vitamin B12, according to the NIH's Office of Dietary Supplements.
There is not yet enough scientific evidence to determine if vitamin B12 supplements have an effect on allergies, multiple sclerosis, psoriasis and other immune system problems. And there is too little evidence to see if vitamin B12 has an effect on Lyme disease, signs of aging, fatigue or chronic fatigue syndrome, according to the National Library of Medicine.
However, vitamin B12 is possibly effective at preventing age-related macular degeneration, a common eye condition that leads to vision loss. Limited research supports that vitamin B12 supplements are effective at treating shaky leg syndrome, eczema and canker sores. However more studies are needed to prove the connection, according to the National Library of Medicine.
How do B12 levels change as people age?
In a 2016 study, researchers measured the levels of vitamin B12 in the brains of more than 60 deceased individuals, ranging in age from a fetus in a late stage of gestation to 80 years. The study, published in the journal PLOS ONE, was the first to compare the levels of vitamin B12 in the brain across the human lifetime.
The researchers found that levels of vitamin B12 in the brain were 10 times lower in the oldest people compared with the youngest, reflecting a gradual, natural and consistent decline over time. But in people with certain medical conditions, the researchers detected levels of the vitamin that didn't fit into this pattern. For example, the brains of young people with autism and the brains of middle-age people with schizophrenia had about one-third the levels of vitamin B12 compared with similarly aged people who did not have these conditions.
The study, however, found only an association between vitamin B12 levels and these neurological conditions; it did not find that low levels of the vitamin lead to the conditions.
Are vitamin B12 supplements safe?
Vitamin B12 has a low risk of overdose in the body. Supplement makers put a lot of B vitamins into capsules — sometimes as much as 200 percent of the recommended daily intake.
"Because they are water soluble, humans can pee out excess vitamins safely," Mangieri said.
For this reason, the Institute of Medicine does not set a limit on how much vitamin B12 a person can safely take in a day. Vitamin B12 also appears to be safe when applied to the skin to treat psoriasis, according to the National Library of Medicine.
Vitamin B12 may increase the risk that an artery narrows around a stent, a device that widens a blocked artery. And vitamin B12 supplements can potentially harm the optic nerve and cause blindness in people with the rare hereditary condition called Leber's disease.
Medications that interfere with vitamin B12 supplements
Common treatments for heartburn and GERD (gastroesophageal reflux disease), also known as acid reflux, such as H2 blockers and proton-pump inhibitors, may contribute to a vitamin B12 deficiency.
Proton-pump inhibitors slow the release of gastric acid, which is needed to start digesting and absorbing vitamin B12 found in food. But studies have yet to conclude if proton-pump inhibitors interfere enough with digestion to result in low vitamin B12 levels. The NIH's Office of Dietary Supplements recommends that doctors monitor the vitamin B12 status of patients on proton-pump inhibitors.
H2 blockers can interfere with vitamin B12 absorption because they slow the release of hydrochloric acid in the stomach. H2 inhibitors could cause problems in people who do not get enough vitamin B12 and who take the medication for more than two years, according to the NIH's Office of Dietary Supplements.
Other drugs that affect stomach acid have been linked to poor vitamin B12 absorption, including the cholesterol drug cholestyramine; the antibiotics chloramphenicol and neomycin; and the gout treatment colchicine.
The diabetes drug metformin may interfere with the body's absorption of vitamin B12 not through stomach acid, but because of the drug's effect on calcium, which is also needed to absorb vitamin B12. More research is needed to determine if calcium supplements may help vitamin B12 absorption in diabetes patients, according to the Linus Pauling Institute at Oregon State University.
Potassium supplements may reduce the body's ability to absorb vitamin B12, as can heavy drinking for more than two weeks, according to the National Library of Medicine.
Large amounts of folic-acid supplements don't interfere with vitamin B12 absorption, but folic acid can mask the symptoms of a vitamin B12 deficiency. Folic acid can correct a condition called megaloblastic anemia, which is caused by low vitamin B12 levels. A person who has this condition won't experience symptoms of anemia, but an underlying vitamin B12 deficiency will still damage the nervous system. The NIH's Office of Dietary Supplements recommends healthy people get no more than 1,000 micrograms of folic acid per day.
This article is for informational purposes only, and is not meant to offer medical advice.
Editor's Note: This article was first published on Aug. 15, 2014. Live Science's Rachael Rettner updated the article on June 21, 2017.