VITAMIN B12 – FACT SHEET

FOOD SOURCES: Meat (beef, liver), fish (tuna), eggs, milk, cheese, and, fortified foods. Plant sources like spirulina and chlorella contain only the biologically inactive form. Nori and shiitake are plant sources too.

The most absorbable forms are methylcobalamin, adenosylcobalamin, and hydroxycobalamin. I do NOT recommend the synthetic form (cyanocobalamin) even though it is found in many supplements (because it is cheap and stable).

Vitamin B12 is needed to form red blood cells and DNA. It is also a key player in the function and development of brain and nerve cells.

70% is retained during cooking (for example it is lost in large amounts when milk is pasteurized).

Vitamin B12 binds to the protein in the foods we eat. In the stomach, hydrochloric acid and enzymes like pepsin unbind vitamin B12 into its free form. From there, vitamin B12 combines with a protein called intrinsic factor (IF) so that it can be absorbed further down in the small intestine.

The RDI for vitamin B12 ranges from 2.4 mcg for adults to 2.8 mcg for breastfeeding women.

Supplemental range: 300-8000 mcg/day

Who needs supplementation? Vegans, pregnant women, and people with thyrotoxicosis, malignancy, liver and kidney diseases.

The most common cause of deficiency is malabsorption due to inadequate IF (pernicious anaemia). Deficiency causes:

- impaired cell division leads to megaloblastic anaemia.

- B12 insufficiency leads to folate deficiency because B12 is essential for folic acid metabolism

- Neurological abnormalities: progressive neuropathy with nerve demyelination (numbness, tingling, burning sensation, weakness in legs). Once experienced the symptoms can be irreversible. Deficiency can come from long-term vegans or vegetarians who rarely consume dairy.