What’s the Best Way to Take Vitamin B-12? Dosage and Absorption Tips

Answer:

Vitamin B-12 is a water-soluble vitamin that is part of the B vitamin family. Many people do not get enough B-12 either due to their diets or absorption issues. Below, we explain why vitamin B-12 is important, recommended dosages for different people, different forms of B-12, the best way to take B-12 supplements, B-12 side effects, and more. If you need to take a B-12 supplement, be sure to see our Top Pick for B-12 among products that we have tested in our B Vitamin Supplements Review.

What is vitamin B-12 and how much do I need?

Vitamin B-12, an essential nutrient also known as cobalamin, helps make the genetic material in cells. Typically, people are not considered B-12 deficient until levels go below 200 pg/mL, although older adults may have symptoms of deficiency at blood levels of 200 to 500 pg/mL (CDC, 2012). It is medically recommended that people over age 50 get at least 2.4 mcg of B-12 daily from supplements or foods fortified with B-12.

For more about why B-12 is important and how much you need (depending on age and gender), see the Vitamin B-12 section of the B Vitamin Supplements Review. Also see our Top Pick for B-12 supplements.

What are the benefits of supplementing with B-12?

In addition to treating a B-12 deficiency or maintaining healthy B-12 levels, supplementing daily with vitamin B-12 (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 B-12 from your diet or not able to extract it from foods — a common problem in older people (Ueno, Nutrients 2022; Walker, Am J Clin Nutr 2012; de Jager, Int J Geriatr Psy 2011).

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 (Oulhaj, J Alz Dis 2016). Getting the recommended daily allowance of B-6 (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 B-12 among products we have tested. The Review also includes information about good food sources of vitamins B-12.

Who is likely to have a B-12 deficiency?

Older adults are more likely to experience B-12 deficiency (CDC, 2012). Strict vegetarians or vegans (Storz, Nutrition 2024; Haddad, Am J Clin Nutr 1999), and people taking medications that decrease stomach acid, such as Prevacid and Prilosec (Lerman, Am J Med Sci 2022; Lam, JAMA 2013), or those taking the anti-diabetes drug metformin (Yao, Commun Biol 2023), are also more likely to become deficient. B-12 supplements can correct a deficiency, and B-12 injections are typically not necessary. For more information about who is at risk for B-12 deficiency, see the B Vitamin Supplements Review.

What are symptoms of B-12 deficiency?

A B-12 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 (Maharajh, N Engl J Med 2022; Briani, Nutrients 2013; Jansen Ned Tijdschr Geneeskd 2013; Bromley, Am Fam Physician 2000). In some cases, B-12 deficiency may reduce immunity (Patel, Cureus 2023; Bhattacharjee, Adv J Emerg Med 2019).

For more details about symptoms of B-12 deficiency, see the Vitamin B-12 section of the B Vitamin Supplements Review. Also see our Top Pick for B-12 supplements.

What is the best way to take vitamin B-12?

There are different forms of B-12 available (cyanocobalamin, methylcobalamin, and hydroxocobalamin). Although there are some differences among them, for most people any of these will be effective (Greibe, Eur J Nutr 2017; Obeid, Mol Nutr Food Res 2015; Spence Clin Chem Lab Med 2013). (Some people are concerned about the cyanide molecule in cyanocobalamin, but this form of B-12 is very safe except for individuals with kidney failure.)

Vitamin B-12 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 B-12 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 (Grembecka, Eur Food Res Technol 2015). 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 B-12 within a given period of time (Del Bo, Clin Nutr 2019; Institute of Medicine (US) Food and Nutrition Board 1998). To absorb more B-12, divide the dose over the course of the day and take separately from a B-12-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 B-12 section of the B Vitamin Supplements Review.

Should I consider vitamin B-12 injections or patches?

Vitamin B-12 injections may be necessary if you have severe neurological symptoms due to a B-12 deficiency (Kolber, Can Fam Physician 2014; Andres, Expert Opin Pharmacother 2010). 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 (Lacombe, Am J Clin Nutr 2024; Ramos, Obes Res Clin Pract 2021). For more about this and symptoms of B-12 deficiency, see the Vitamin B-12 section of the B Vitamin Supplements Review.

Patches containing vitamin B-12 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. However, these patches might not be a good alternative (Saurabh, Obes Surg 2019; Yang, Pharmaceutics 2011; US Patent Application 20080160070). Find out why in our article, Do vitamin patches, such as for B-12 or multivitamins, really work?

What are side effects of vitamin B-12?

Many vitamin supplements contain more B-12 than necessary and can be absorbed. Furthermore, it is now acknowledged that you need less of many B vitamins than believed in the past. Until 2016, the Daily Value for vitamin B-12 was 6 mcg, but it has since been lowered to 2.4 mcg for most people 14 years and older.

Getting too much B-12 may cause adverse effects, including rosacea and acne (Jansen, J Eur Acad Dermatol Venereol 2001; Sherertz, Cutis 1991). Additionally, a B-complex supplement providing 1,000 mcg of B-12 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 (Cappello, Nutrients 2017). Although rare, allergic reactions to vitamin B-12 have been reported (El Rhermoul, J Allergy Clin Immunol Pract 2023; Pegalajar-García, Contact Dermatitis 2023). In addition, higher blood levels of vitamin B-12 have been linked with greater risk of dying from any cause or from heart disease (Liu, JAMA Netw Open 2022; Flores-Guerrero, JAMA Network Open 2020) and with insomnia (Xiong, Nutr Diabetes 2022; Morales-Gutierrez, Clin Toxicol (Phila) 2020), although a direct cause-and-effect relationship with these latter adverse effects has not been established.

Be aware that certain B vitamins can interact with other drugs and supplements. For more details, see the Vitamin B-12 section of the B Vitamin Supplements Review. Also see our Top Pick for B-12 supplements.