Vitamin B12: Absorption, actions and animal foods

Published June 25, 2021

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What is vitamin B12

Vitamin B12 is an essential water‐soluble vitamin that you get from your food. It plays a vital role in your health and insufficiency can cause a wide range of symptoms. Understanding how vitamin B12 is absorbed, what can impact that absorption and which foods contain vitamin B12 can help you prevent a vitamin B12 insufficiency.

Vitamin B12 absorption

Absorbing vitamin B12 involves your stomach and your lower intestine, and being aware of factors that can impair absorption can help you prevent a vitamin B12 insuffiency.

Your food releases its B12 in the stomach with the help of gastric acid and a protein called intrinsic factor; the B12 is then absorbed in the lower small intestine.

After absorption in the lower small intestine vitamin B12 is transferred to sites around the body by three carriers, transcobalamin I, II and III. The two active forms of vitamin B12 are adenosylcobalamin — found mainly in cellular tissues, and methylcobalamin — found mainly in the blood.

Older people are at risk of developing vitamin B12 insufficiency because of loss of intrinsic factor or through decreased secretion of the gastric acid necessary to release the vitamin from food. (The B12 found in vitamin supplements, however, can continue to be well absorbed even in people with decreased stomach acid).

Reduction of gastric acid in later life may be caused by inflammation of the stomach or from medications that reduce gastric acid in the stomach.

Intrinsic factors may be lacking due to an autoimmune condition, or due to surgical removal of the part of the stomach where intrinsic factor is made.

Other conditions that can contribute to inadequate B12 absorption include:

  • Overgrowth of bacteria in the small intestine.
  • Impaired absorption.
  • Surgery that removes the part of the small intestine where vitamin B12 is absorbed.

How much B12 do I need every day?

The recommended daily requirement of vitamin B12 for adults is two‐five micrograms, and the average adult daily intake from an unrestricted diet is five‐thirty micrograms, with around ten to thirty per cent being destroyed by cooking.

Is vitamin B12 stored in the body?

Your body stores approximately two-five milligrams of B12 mainly in the liver.

What does B12 do in the body?

Vitamin B12 is needed for the formation and maturation of red blood cells and to make DNA. Vitamin B12 is also needed for normal nerve function. Vitamin B12 supports energy and helps breakdown fats, carbohydrates and proteins from your diet. Vitamin B12 also supports cognition.

Who is most at risk of vitamin B12 insufficiency?

  • Vegans — People who don’t eat any meat, dairy, or eggs are most at risk for developing a B12 insufficiency. Aside from fortified breakfast cereals, the only reliable dietary sources of vitamin B12 are animal-derived foods. Vegetarians who eat eggs and dairy products still may not consume enough vitamin B12 in their diet to meet requirements.
  • Older people — Some older people are also at high risk for developing B12 insufficiency. Up to 30% of people ages 50 and over suffer thinning of the stomach lining. This reduces the amount of vitamin B12 absorbed by the small intestine.

What are the symptoms of vitamin B12 insuffiency?

Symptoms of vitamin B12 insufficiency can include:

  • Paleness
  • Weakness
  • Fatigue
  • Shortness of breath and dizziness.
  • Severe vitamin B12 insufficiency may lead to nerve damage.

How do I get vitamin B12 in my diet?

Sources of vitamin B12 include:

  • Seafood including clams, mussels, crab, salmon
  • Beef
  • Chicken
  • Eggs (whole)
  • Milk

Vitamin B12 supplementation

Vitamin B12 is available in two forms of supplements:

  • Cyanocobalamin — Cyanocobalamin is the synthetic form of vitamin B12 most commonly used in supplements. When it enters your body, it’s converted into either methylcobalamin or adenosylcobalamin, which are the two active forms of vitamin B12. Nature’s OwnTM Vitamin B12 1000 mcg is available in a convenient one a day dose.
  • Activated Methyl B12 tablets — Activated Methyl B12 or mecobalamin is the active form of vitamin B12 found in the body. It can participate directly as a coenzyme for metabolic reactions without having to be converted. Nature’s OwnTM Activated Methyl B12 1000mcg tablets are available in a sublingual form and are dissolved directly under the tongue to bypass gastric absorption.

Vitamin B12 is an essential vitamin needed to make red blood cells, metabolise nutrients and synthesis DNA. It is absorbed by the body via an intricate system involving the stomach and small intestine, leading to potential absorption issues for the elderly or people with gut conditions. Including animal foods in your diet or supplementing with vitamin B12 can help maintain healthy vitamin B12 levels, supporting energy, cognitive function and red blood cell production. Always read the label. Follow the directions for use. If symptoms persist, talk to your health professional.

Learn about which Nature's Own product may be appropriate for you.

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