The recommended daily allowance (RDA) for Vitamin B12 ranges from 0.4 to 2.8mcg per day. The daily value (DV) for vitamin B12 is 2.4mcg per day. (3) In 2016, this was reduced from 6mcg per day, because the scientific evidence shows that 2.4mcg is enough to prevent symptoms of deficiency in the majority of people.

Vitamin B12 comes in multiple different forms, including methylcobalamin, cyanocobalamin, and hydroxycobalamin. All of these forms are bioavailable, and are converted within the body to active forms of the vitamin. Some evidence does suggest that cyanocobalamin may be somewhat more bioavailable than other forms. (5)

Intrinsic factor is a protein produced in the stomach, which is required for the absorption of vitamin B12. This limits the amount of B12 that can be absorbed in the digestive tract. For people whose bodies don't make enough intrinsic factor, very little vitamin B12 can be absorbed. (6)

Because of this, many people receive their supplemental B12 through injections, to bypass the digestive tract and allow the vitamin to enter the bloodstream directly. (7)

Another option is to take very high doses of oral vitamin B12, which has also been shown to be an effective way to address vitamin B12 deficiency in people with pernicious anemia. (8)

Further, an intranasal vitamin B12 gel also exists as a way to boost vitamin B12 levels. Talk to your doctor or primary care provider about this method, if you prefer it over injections. (9)

Nori is the thin dried seaweed wrap typically used to make sushi rolls. Studies have found that nori nori seaweed contains up to 51.7mcg of vitamin B12 in 100 grams. (10) A sheet of nori typically weighs 1.25 grams so a single sheet would provide aabout 0.5mcg of vitamin B12 (8% DV).

While this sounds great, it is unlikely that nori can be relied upon to be a consistent B12 source. While it does make a good addition to a balanced vegan diet, it should not be solely relied upon to provide a person's vitamin B12 needs.

• Protection Against Heart Disease - Adequate levels of vitamins B12, B6, and B9 have been shown to lower levels of a protein in the blood known as homocysteine. High levels of homocysteine have been shown to cause damage to blood vessels, and lowering the levels of this substance can help to improve blood vessel function, which in turn may boost cardiovascular health and decrease the risk of heart attacks. (11)
• Protect and Repair DNA to Reduce Cancer Risk and Slow Aging - Absorption of vitamin B12 and Folate (B9) is essential for DNA metabolism and maintenance, which may reduce the risk of cancer and slow down aging. (12)
• Protect Against Dementia and Cognitive Decline - Vitamin B12 is important for nervous system functions, including cognition and memory. Some studies have linked low vitamin B12 levels and high homocysteine levels to an increased risk of cognitive impairment and dementia. In people with vitamin B12 deficiency, replacing B12 has been shown to lead to memory improvements in many cases. Although more research is needed to confirm this association, it's currently believed that maintaining adequate vitamin B12 levels could help to reduce the risk of dementia. (13)
• Energy and Endurance - Vitamin B12 deficiency leads to anemia, low energy, and weakness. (1) Adequate levels of vitamin B12 are necessary to maintain normal energy levels. However, in people who have normal B12 levels, taking extra B12 has not been shown to improve athletic performance or lead to increased energy levels. (14)

Cows are not given any form of synthetic vitamin B12. Vitamin B12 is naturally synthesized by bacteria that flourish in certain animals although not in humans. (1) Cows and other ruminants (such as sheep and goats) ferment their food in 4 different stomachs as they digest it. The bacteria involved in this fermentation also create vitamin B12, and this vitamin then enters the animal's flesh and milk.