Vitamin B12 is essential to keeping your body's cells healthy. While its benefits could be considered subtle, this vitamin is so important that your nervous system won't function properly without it.
Consuming too little vitamin B12 can result in side effects that range from gastrointestinal discomfort to serious neurological problems.
Here's what you should know about this crucial nutrient, including how to know if you're getting enough.
Benefits of Vitamin B12
Vitamin B12, also known as cobalamin, is an essential nutrient that is important for the health and maintenance of your cells. Your body needs it to make red blood cells, create DNA and maintain the functionality of your nervous system. Plus, per a 2014 study in BioMed Research International, vitamin B12 (along with other B-complex vitamins) can even help decrease the severity of migraines. Most people need just 2.4 micrograms of B12 each day to obtain its benefits, according to the National Institutes of Health's Office of Dietary Supplements.
Vitamin B12 in foods and B12 supplements are two different things. When you eat food containing B12, your body needs to isolate it in order to absorb it. This involves the hydrochloric acid in your stomach separating the vitamin from the food it's found in and combining it with intrinsic factor, a glycoprotein in your stomach. This process allows your body to absorb and use the vitamin.
Artificially produced vitamin B12 found in a supplement doesn't need to be broken down the way the natural vitamin does. However, it is poorly absorbed by the body in this state, and only about half of each microgram of synthetic B12 actually gets absorbed. (This is why the dosage may be high.)
Vitamin B12 deficiency can be a serious health problem, according to the European Journal of Clinical Nutrition. If you don't get enough, you might experience side effects like:
- Tiredness and weakness
- Gastrointestinal problems, like constipation or unexplained weight loss
- Loss of appetite
- Tingling or numbness in your hands and feet
- Balance issues
- Confusion and memory issues
- Problems with your oral health, like sore tongue and mouth
Certain people are more likely to be vitamin B12-deficient than others. Those who are over age 50, people with certain health conditions and pregnant women should consider taking supplements.
Vitamin B12 is most commonly found in animal products, so vegetarians and vegans tend to be more likely to experience B12 deficiency. Those who otherwise don't consume animal products, plant-based sources of vitamin B12 or fortified foods should consider supplements.
Some people don't produce enough intrinsic factor, which makes it difficult for their bodies to absorb enough vitamin B12 from food. This happens regardless of whether or not they're eating foods rich in this nutrient. Without intrinsic factor, your body may only be able to absorb about 1 percent of a B12 supplement. This means that people lacking intrinsic factor may need a high dosage to avoid a deficiency.
Natural Sources of B12
Animal products like shellfish, fish, meat, milk products and eggs are all well-known sources of vitamin B12. Many of these products can provide you with far more than the recommended dietary allowance (2.4 micrograms) of vitamin B12. For example, a single 3-ounce serving of cooked clams has about 99 micrograms of vitamin B12, while a serving of pan-fried beef liver has 83 micrograms.
You can also grab some B12 from certain vegetables and other foods. Mushrooms — like black trumpet, golden chanterelle and shiitake mushrooms — contain the vitamin. Every 100 grams of mushrooms may supply between 1.09 to 5.61 micrograms of vitamin B12, according to a May 2014 study published in Nutrients.
Furthermore, many different types of algae, as well as sea plants, like sea buckthorn berries, sidea couch grass and elecampane, all contain B12 — some in substantial amounts, per a January 2018 paper in Experimental Biology and Medicine. While certain sea plants have no vitamin B12, many have about 11 to 37 micrograms per 100 grams of the food. Certain types of algae can have even more vitamin B12, with about 77 micrograms per 100 grams on average, and as much as 415 micrograms per 100 grams in specific varieties.
Since B12 is most commonly found in animal products, many plant-based products, grains and yeast are fortified with it in order to make it more accessible to everyone, according to an August 2014 review in the Journal of Food Science and Technology. Many breakfast products you're probably familiar with — like Cheerios, Raisin Bran, Corn Flakes and Honey Bunches of Oats — contain this essential nutrient. And it's actually possible to obtain all of your recommended dietary allowance of B12 from cereals like these. In fact, there's even some concern that certain products are excessively fortified.
Fermented foods also contain vitamin B12. A December 2016 study published in Nutrients showed that B12 content can increase in fermented foods through the use of lactic acid or propionic bacteria. This means that foods like tempeh, sauerkraut and kimchi can all contain the vitamin. The amount of B12 in these products can range between 0.7 and 10 micrograms per 100 grams of food.
The way your vegetables are grown also influences their vitamin B12 content. Both organic fertilizers and hydroponic techniques are able to increase levels of vitamin B12 in produce. However, these methods can really only help supplement your diet with this nutrient, since they're not yet able to provide you with the complete recommended dietary amounts.
B12 Supplements and Side Effects
Anyone who doesn't eat enough foods containing vitamin B12 and may be deficient should consider taking supplements. A 2018 study in the Cochrane Database of Systematic Reviews showed that both oral and injectable B12 supplements can resolve even serious deficiency-related side effects.
Another study, though, found that there may be a drawback to B12 supplementation. In the study, which included 75,000 American women and was published May 2019 in JAMA Network Open, researchers found that high intakes of vitamins B6 and B12, through food and supplements, was associated with a higher risk of hip fracture. But supplementing with B12 alone does not increase this risk.
Although the normal vitamin B12 dosage is just 2.4 micrograms per day, vitamin B12 supplements may be sold in pills containing thousands of micrograms. Granted, this might seem excessive, but large amounts of B12 supplements have been clinically recommended for many years. Such large amounts are particularly necessary for people who lack intrinsic factor, and remember that only a small amount of synthetic vitamin B12 is absorbed by your body.
Lastly, since vitamin B12 is a water-soluble vitamin, it's excreted whenever you urinate. Whether you're getting this nutrient naturally from foods or from a supplement, any excess will usually be removed from your body. In fact, your body will struggle to absorb B12 after a certain point since you only have so much intrinsic factor. This means that even if you take in too much vitamin B12, any side effects will be limited and will likely go away as soon as you stop supplementation.
- BioMed Research International: "Vitamin Supplementation as Possible Prophylactic Treatment Against Migraine With Aura and Menstrual Migraine"
- National Institutes of Health Office of Dietary Supplements: "Vitamin B12: Fact Sheet for Health Professionals"
- European Journal of Clinical Nutrition: "The Prevalence of Cobalamin Deficiency Among Vegetarians Assessed by Serum Vitamin B12: A Review of Literature"
- Nutrients: "Vitamin B12-Containing Plant Food Sources for Vegetarians"
- Experimental Biology and Medicine: "Vitamin B12 Sources and Microbial Interaction"
- Journal of Food Science and Technology: "Significance of Coarse Cereals in Health and Nutrition: A Review"
- Environmental Working Group: "How Much Is Too Much?: EWG Identified 23 Excessively Fortified Cereals"
- Nutrients: "Vitamin B12 Among Vegetarians: Status, Assessment and Supplementation"
- Cochrane Database of Systematic Reviews: "Oral Vitamin B12 Versus Intramuscular Vitamin B12 for Vitamin B12 Deficiency"
- Harvard Health Publishing: "Getting Enough Vitamin B12"
- USDA FoodData Central: "Beef, variety meats and by-products, liver, cooked, pan-fried"
- USDA FoodData Central: "Mollusks, clam, mixed species, cooked, moist heat"
- JAMA Network Open: "Association of High Intakes of Vitamins B6 and B12 From Food and Supplements With Risk of Hip Fracture Among Postmenopausal Women in the Nurses’ Health Study"