Vitamin B12 doesn't exactly top the list of the most talked-about nutrients. (All too often, that distinction goes to calcium or vitamin D.) But take a closer look, and you'll see B12 is a vital nutrient that helps keep just about every part of your body healthy.
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"Vitamin B12 is critically important for the development and function of the central nervous system," says Leslie Bonci, MPH, RD, a dietitian based in Pittsburgh and former spokesperson for the Academy of Nutrition and Dietetics, who calls B12 the "puppeteer" of the body. "And it's really important that we have enough B12 for red blood cell formation and for the synthesis of DNA."
Here's a closer look at the benefits of vitamin B12, as shown by research — along with some of the yet unproven claims.
Proven Benefits of Vitamin B12
There's no denying the importance of B12. We know this because people who are deficient in the vitamin are at risk for conditions such as anemia — and deficiencies may be more common than you think.
Because vitamin B12-rich foods include animal products such as fish, meat, poultry, eggs and milk, vegetarians and vegans are especially at risk for a deficiency, according to a March 2014 review in the European Journal of Clinical Nutrition.
An increase in strict vegan and vegetarian diets has led to an uptick in people who have vitamin B12 deficiencies, says Naveen Mahmood, MD, a family medicine physician at UT Health, The University of Texas Health Science Center in Houston, Texas. "We see vitamin B12 deficiencies all the time," she says.
People with certain autoimmune conditions — such as Crohn's disease (an inflammatory bowel disease that causes bloating, gas, abdominal cramps and more), for example — are also at risk for a deficiency, Dr. Mahmood says.
"Vitamin B12 is absorbed in your gut, mainly in the last part of your small intestine called the ilium," she explains. Because people with Crohn's disease have inflammation in the ileum, they can also have trouble absorbing the vitamin.
Here's why it's important to make sure you're getting enough B12.
How Much B12 Do You Need?
People over the age of 18 — both those assigned male at birth (AMAB) and assigned female at birth (AFAB) — need 2.4 micrograms (mcg) of vitamin B12 daily (pregnant people need 2.6 mcg; those who are lactating need 2.8 mcg), according to the National Institutes of Health’s Office of Dietary Supplements (ODS).
1. Helps Prevent Anemia
This differs from iron-deficiency anemia, which is caused by low iron levels; iron is a mineral that's in red blood cells. People with heavy periods are at risk for iron-deficiency anemia because they lose blood during menstruation.
People who've had gastrointestinal surgery or those who have celiac disease or inflammatory bowel diseases (IBD) such as Crohn's disease may also have trouble absorbing vitamin B12 in the small intestine, which can lead to anemia.
Excessive alcohol consumption can lead to anemia as well, because it decreases your body's ability to absorb vitamins in the GI tract, according to the American Addiction Centers. Heavy drinking is defined as more than four drinks per day (or more than 14 per week) for people AMAB and more than three drinks per day (or more than seven per week) for people AFAB.
But even moderate alcohol consumption can affect your B12 absorption over time, especially if you have other risk factors for a deficiency.
2. Helps Reduce the Risk of Birth Defects
Vitamin B12 is important for a developing baby's brain, and a deficiency during pregnancy can cause permanent brain and spine defects.
A September 2014 study in Pediatrics found babies born to people with the lowest blood levels of vitamin B12 were two to three times more likely to have a neural tube defect, or severe defects of the brain and spine, than babies born to those with the highest blood levels of B12. (The neural tube forms the baby's early brain and spine; common neural tube defects include spina bifida and anencephaly).
A September 2017 paper in American Family Physician noted being deficient in vitamin B12 during pregnancy can also lead to developmental delays, decreased muscle tone and more.
Many prenatal vitamins contain more than enough of the recommended amounts, but pregnant people who don't take a prenatal and follow a vegetarian or vegan diet may not be getting enough B12.
Vitamin B12 is not the same as folate (vitamin B9), which is typically found in prenatal vitamins in the form of folic acid and is known to help prevent birth defects of the brain and spine. However, the two B vitamins work together in the body to help make red blood cells, help iron work better in the body and to support immune function and mood, per Mount Sinai. That's why it's so important to get adequate amounts of both vitamins, especially if you're pregnant.
Unproven Claims About Vitamin B12
Sure, your body needs vitamin B12, but you only need so much of it. The problem is, many people think by taking B12 supplements, they can increase their energy levels, boost their memory and improve their mood.
But unless you're deficient in the vitamin, upping your intake isn't likely to bring about any more benefits, Dr. Mahmood says.
Here's a list of what vitamin B12 hasn't been proven to do (at least, not yet), according to science.
1. Heart Disease
It's true that vitamin B12 can help lower a person's levels of homocysteine — an amino acid found in the body that, in too-high amounts, can increase the risk of heart disease.
However, recent studies have found supplementing with vitamin B12 (along with other B vitamins) hasn't prevented heart attacks or lowered the risk of heart disease, according to the ODS.
People get energy from calories — and the only sources of calories are protein, carbs and fat, Bonci says. Because vitamins don't contain calories, they can't technically boost your energy levels, she says.
However, if someone is deficient in vitamin B12, they can develop anemia, which can cause symptoms like fatigue, muscle weakness, pale skin and weight loss, per the Mayo Clinic.
Once that person corrects the deficiency, they may feel like they have more energy, but that's not because vitamin B12 is a source of energy itself, Bonci says.
Don't expect it to give you an advantage in the gym, either: An older but still-cited July-August 2004 review in Nutrition found unless someone was deficient in B12, supplementing with the vitamin didn't boost athletic performance.
Being deficient in vitamin B12 is associated with dementia and lower levels of cognition (i.e., memory and thought processes), according to the Mayo Clinic. But so far, research hasn't found that taking vitamin B12 supplements can improve a person's cognitive function, according to a January 2007 systematic review of randomized trials in JAMA Internal Medicine (the most current review of its kind on the topic).
One caveat: Being deficient in vitamin B12 can cause confusion and memory loss, Dr. Mahmood says, so treating the deficiency can improve those symptoms.
Keep in mind, too, that the risk for vitamin B12 deficiency increases with age. According to a September 2014 study in The BMJ, the prevalence of vitamin B12 deficiency is about 6 percent in people under the age of 60 — after the age of 60, that number jumps to nearly 20 percent.
Part of the reason is, as we age, our bodies don't absorb vitamin B12 as well, Dr. Mahmood says. Medications, such as those for acid reflex, can also interfere with our ability to absorb B12, and older adults are more likely to take medications to manage conditions.
4. Macular Degeneration
Age-related macular degeneration is an eye disease in which people lose their central vision. In developed countries, it's the leading cause of vision loss in older people, according to the U.S. National Library of Medicine.
Research on vitamin B12 and macular degeneration is limited, but one February 2009 study in the Archives of Internal Medicine found, among people AFAB who were at a high risk of cardiovascular disease, those who took a folic acid, vitamin B6 and vitamin B12 supplement were about 35 to 40 percent less likely to develop age-related macular degeneration than those who took a placebo.
While promising, this research is still in its early stages: A more recent editorial in The American Journal of Clinical Nutrition from July 2013 concluded that, while it's too early to recommend taking B vitamins to prevent age-related macular degeneration, scientists should continue to study the possible link.
Because B vitamins are essential for proper nerve function, some people believe taking B12 can help with nerve repair or treating neuropathy. It's true that people who don't get enough B12 may be at higher risk for neuropathy and other nervous system problems, according to the Mayo Clinic, but it's not clear whether supplementing with B12 can help the condition.
The exception here may be if you're deficient in B12, although the few studies that show a benefit to supplementing have been small.
Indeed, a June 2021 review and meta-analysis in the European Journal of Neurology concluded the available research is too limited, and more well-designed studies are needed.
When it comes to vitamin B12 and cancer, the research is mixed, according to the ODS. That may be putting it mildly — while some studies have found B12 may help prevent some cancers, others have shown high doses of the vitamin can increase the risk of cancer.
For example, one March 2018 meta-analysis in Medicine found getting 10 mcg per day of vitamin B12 can reduce the odds of developing pancreatic cancer by 27 percent. Another September 2015 study in Public Health Nutrition found a link between increased vitamin B12 intake and colorectal cancer.
Of the research that's found a link between high B12 intake and increased cancer risk, one April 2019 study in Cancer Epidemiology, Biomarkers & Prevention, which tracked more than 33,000 people, found those with high blood levels of vitamin B12 were more likely to be diagnosed with cancer after one year than those with lower levels.
Yet another study, published August 2017 in the Journal of Clinical Oncology, found taking vitamin B6 and B12 supplements was linked to a 30 to 40 percent increased risk of lung cancer in people AMAB. What's more, people AMAB who took high doses of vitamins B6 and B12 for 10 years were almost twice as likely to develop lung cancer compared to those who took lower doses.
In short: The jury is still out when it comes to the link between B12 and cancer.
Research hasn't shown that vitamin B12 can help prevent or alleviate depression, a condition that affects about 16 million people in the U.S. each year, according to the Centers for Disease Control and Prevention (CDC).
One October 2020 review in Cureus examined more than 30 studies and concluded there was currently no evidence proving vitamin B12 could improve the symptoms of depression.
The research did, however, find a link between people who had lower levels of vitamin B12 and an increased risk of developing depression. But more research needs to be done to understand that link.
8. Bone Health
Vitamin B12 plays an important role in DNA production, and some researchers have wondered whether the vitamin can also help boost bone formation. So far, the research is mixed.
One older, January 2005 study in the Journal of Bone and Mineral Research found a link between low levels of B12 and lower levels of bone mineral density. (Bone density, or mass, is a way of gauging the strength of your bones — if your bone mass is low, you may have osteoporosis, or weak bones.)
Other research has shown some negative effects of too much B12: A May 2019 study in JAMA Network Open found, among people AFAB, those with high intake of both vitamins B6 and B12 (more than 35 mg per day and 20 mcg per day, respectively) had almost a 50 percent increased risk of hip fracture compared with those who had a low intake (less than 2 mg and 10 mcg per day, respectively).
9. Hair, Skin and Nails
Vitamin B12 is found in many supplements that promise better hair, nails and skin. But if you're already getting enough of the vitamin, it's not clear — and may be unlikely — that you'll reap any extra benefits.
A deficiency, on the other hand, has been linked to skin discoloration, poliosis (a condition in which white patches appear on the hair), and more, according to a January 2015 review in the American Journal of Clinical Dermatology.
Vitamin deficiencies are common in theories about the cause of autism spectrum disorder (ASD), but the truth is we still don't know, and it's likely more complicated than a single deficiency.
With that said, an August 2021 systematic review and meta-analysis in the Journal of Personalized Medicine — which looked at 17 studies that had used B12 as a treatment for ASD — found there's preliminary evidence to suggest supplementing (especially with shots of a form of B12 known as methylcobalamin) may help improve symptoms of the condition.
The authors noted, though, that larger, well-designed studies are necessary to confirm these findings.
11. Other Unproven Benefits
There's no evidence at all to support claims that vitamin B12 can help with the following:
- Canker sores
- Detoxing or "flushing" your system
- Colds or immune health
- Bloating and gas
When to See a Doctor
Some of the most common symptoms of a vitamin B12 deficiency include fatigue, shortness of breath and tingling in the hands and feet, according to the Mayo Clinic. See a doctor if these symptoms sound familiar.
If your doctor suspects you're running low, they may check your levels with a blood test, Dr. Mahmood says. (The results usually come back in a few days, she adds.)
People who have trouble absorbing B12 — such as older adults or those with autoimmune conditions — may need to schedule a routine injection of the vitamin to boost their levels, she says.
But oftentimes, people may just need to take a supplement, which you can find over the counter, or increase their intake by including B12-rich foods in their diet, including fortified cereals and nutritional yeasts.
- American Journal of Clinical Dermatology: "A Review of Vitamin B12 in Dermatology"
- U.S. National Library of Medicine: "Bone Density"
- Centers for Disease Control and Prevention: "Mental Health Conditions: Depression and Anxiety"
- Journal of Clinical Oncology: "Long-Term, Supplemental, One-Carbon Metabolism–Related Vitamin B Use in Relation to Lung Cancer Risk in the Vitamins and Lifestyle (VITAL) Cohort"
- Public Health Nutrition: "A Dose-response Meta-analysis Reveals an Association Between Vitamin B12 and Colorectal Cancer Risk"
- Medicine: "Vitamin Intake and Pancreatic Cancer Risk Reduction"
- National Institutes of Health Office of Dietary Supplements: "Vitamin B12 Health Professional"
- The American Journal of Clinical Nutrition: "Should We Be Taking B Vitamins to Prevent Age-related Macular Degeneration? Not Yet, but Worth Doing More Research"
- Archives of Internal Medicine: "Folic Acid, Vitamin B6, and Vitamin B12 in Combination and Age- related Macular Degeneration in a Randomized Trial of Women"
- U.S. National Library of Medicine: "Age-Related Macular Degeneration"
- The BMJ: "Vitamin B12 Deficiency"
- Mayo Clinic: "Vitamin B-12"
- Centers for Disease Control and Prevention: "Facts About Neural Tube Defects"
- Mayo Clinic: "Iron Deficiency Anemia"
- Pediatrics: "Maternal Vitamin B12 Status and Risk of Neural Tube Defects in a Population With High Neural Tube Defect Prevalence and No Folic Acid Fortification"
- Cancer Epidemiology, Biomarkers & Prevention: "Elevated Vitamin B12 Levels and Cancer Risk in UK Primary Care: A THIN Database Cohort Study"
- Mayo Clinic: "Diabetic neuropathy: Can dietary supplements help?"
- European Journal of Neurology: "Association between neuropathy and B-vitamins: A systematic review and meta-analysis"
- Journal of Personalized Medicine: "The Effectiveness of Cobalamin (B12) Treatment for Autism Spectrum Disorder: A Systematic Review and Meta-Analysis"
- Centers for Disease Control and Prevention: "Folic Acid Helps Prevent Serious Birth Defects of the Brain and Spine"
- Mount Sinai: "Vitamin B12 (Cobalamin)"
- American Addiction Centers: "Anemia and Alcohol Abuse"