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B12: Dosage, Health Benefits, Uses and Deficiency

Question:
What is vitamin B12 and how much do I need?
Reviewed and edited by Tod Cooperman, M.D. Tod Cooperman, M.D.
Initial Posting: 6/30/2017    Last Update: 4/20/2020
Vitamin B12 Dosage, Benefits, Uses & Deficiency -- B12 Bottle and Tablets
Answer:
What is vitamin B12 and how much do I need?
What are the benefits of supplementing with B12?
Who is likely to have a B12 deficiency?
What is the best way to take vitamin B12?
Should I consider vitamin B12 injections or patches?
What are side effects of vitamin B12?

Vitamin B12 is a water-soluble vitamin that is part of the B vitamin family. Many people do not get enough B12 either due to their diets or absorption issues. Our CL Answer below explains why B12 is important, the recommended dosages for different people, the different forms of B12, the best way to take B12 supplements, B12 side effects, and more. If you need to take a B12 supplement, be sure to see our Top Pick for B12 among products that we have tested in our B Vitamin Supplements Review.

What is vitamin B12 and how much do I need?

Vitamin B12, an essential nutrient also known as cobalamin, helps make the genetic material in cells. Typically, people are not considered B12 deficient until levels go below 200 pg/mL, although older adults may have symptoms at blood levels of 200 to 500 pg/mL. It is medically recommended that people over age 50 get at least 2.4 mcg of B12 daily from supplements or foods fortified with B12.

For more about why B12 is important and how much you need (depending on age and gender), see the Vitamin B12 section of the B Vitamin Supplements Review. Also see our Top Pick for B12 supplements.

What are the benefits of supplementing with B12?

In addition to treating a B12 deficiency or maintaining healthy B12 levels, supplementing daily with vitamin B12 (100 mcg to 500 mcg) and, possibly, folic acid (400 mcg), may help slow age-related declines in memory and cognition if you're not already getting enough vitamin B12 from your diet or not able to extract it from foods -- a common problem in older people.

This benefit may be enhanced when you're also getting a good amount of omega-3 fatty acids (DHA and EPA), such as from oily fish like salmon. Getting the recommended daily allowance of B6 (about 1.7 mg), which is easily obtained from foods, is also important.

For more details see the Memory, Cognition, and Alzheimer's Disease section of the B Vitamins Review, which includes our Top Pick for B12 among products we have tested. The Review also includes information about good food sources of vitamins B12.

Who is likely to have a B12 deficiency?

Older adults are more likely to experience B12 deficiency. Strict vegetarians and people taking medications that decrease stomach acid, such as Prevacid and Prilosec, or those taking the anti-diabetes drug metformin, are also more likely to become deficient. B12 supplements can correct a deficiency, and B12 injections are typically not necessary.

A B12 deficiency can have wide-ranging effects. These commonly include anemia, as well as fatigue, depression, tingling in the arms and legs, loss of balance, as well as skin and hair changes. In some cases, B12 deficiency may reduce immunity.

For more details about B12 deficiency, see the Vitamin B12 section of the B Vitamin Supplements Review. Also see our Top Pick for B12 supplements.

What is the best way to take vitamin B12?

There are different forms of B12 available (cyanocobalamin, methylcobalamin, and hydroxocobalamin). Although there are some differences among them, for most people any of these will be effective. (Some people are concerned about the cyanide molecule in cyanocobalamin, but this form of B12 is very safe except for individuals with kidney failure.)

Vitamin B12 is commonly sold as pills, but also as quick-dissolving tablets, sublingual tablets, and sprays. It's not clear that any of these other formulations offer a biological advantage as most of the B12 from these is likely just swallowed and absorbed through the gut. Be aware that to improve taste, some formulations other than pills include sugar substitutes (such as mannitol, sorbitol, and/or sucralose) and, in some people, these can cause gas, bloating, and diarrhea. These side-effects are more likely if taking multiple units.

Most importantly, be aware that your body can only efficiently absorb a small amount of B12 within a given period of time. To absorb more B12, divide the dose over the course of the day and take separately from a B12-containing meal. If you take a higher dose, such as 100 mcg, you will absorb only about 1% of the amount above 2.4 mcg -- although this may be appropriate in some situations. For details, see the Vitamin B12 section of the B Vitamin Supplements Review.

Should I consider vitamin B12 injections or patches?

Vitamin B12 injections may be necessary if you have severe neurological symptoms due to a B12 deficiency. If you do not have severe neurological symptoms, however, research suggests that oral supplementation can effectively treat B-12 deficiency — even in people who have compromised absorption due to lack intrinsic factor or other reasons. For more about this and symptoms of B12 deficiency, see the Vitamin B-12 section of the B Vitamin Supplements Review.

Patches containing vitamin B12 and/or other vitamins, such as those from PatchMD and Vita Sciences, are often promoted as an alternative to oral supplements for people who have trouble swallowing pills or have difficulty absorbing nutrients in their gut. We looked into the research behind these patches. Find out if they are truly a better alternative.

What are side effects of vitamin B12?

Many vitamin supplements contain more B12 than necessary and can be absorbed. Furthermore, it is now acknowledged that you need less of many B vitamins than believed in the past, but "% Daily Value" figures on labels don't have to reflect this until the beginning of 2021. For B12, the Daily Value was reduced from 6 mcg to 2.4 mcg.

Getting too much B12 may cause adverse effects, including rosacea and acne. Additionally, a B-complex supplement providing 1,000 mcg of B12 daily was found to increase the risk of heart attack, stroke and death in people with type 1 or type 2 diabetes who had advanced kidney disease.

Be aware that certain B vitamins can interact with other drugs and supplements. For more details, see the Vitamin B12 section of the B Vitamin Supplements Review. Also see our Top Pick for B12 supplements.

Learn More About Vitamin B12:



Can taking too much vitamin B-12 be dangerous? The label on my B-complex states it contains 50,000% of the Daily Value!  >>

Is sublingual vitamin B-12 really better than the pill form? >>

I read on your website that some B-12 vitamins can cause diarrhea due to added sugar substitutes like sorbitol. I have had diarrhea and never thought it could be caused by my vitamin B-12 supplement, until I read your article and stopped taking the supplement. My diarrhea stopped immediately. Can you help me find a brand of B-12 that doesn't contain sorbitol or sugar substitutes that could cause this problem? >>

Do vitamin patches, such as for B12 or multivitamins, really work? How about those from PatchMD?  >>

See other recent and popular questions >>
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This CL Answer initially posted on 6/30/2017. Last updated 4/20/2020.
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