What is the Role of Vitamin B12?

Vitamin B12 is one of the eight B vitamins, all of which are water-soluble. Vitamin B12 has many functions in the body, and as one of my personal training clients in Chelsea discovered to her surprise, there is a danger than vegetarians and vegans are deficient in this key vitamin. She thought that a strict vegetarian diet was the healthiest way to eat, but as her personal trainer I had to explain why this is not the case.

The technical term for vitamin B12 is cobalamin, and it works together with the trace mineral cobalt.

The functions of vitamin B12

B12 is required for the production and function of all the cells of your body, especially in the bone marrow. It is needed for a healthy nervous system, brain function, metabolism of all food groups (protein, carbohydrates, fats), and the production of red blood cells, RNA, and DNA.

Food sources of vitamin B12

Vitamin B12 in a form that can be readily absorbed by the human body is only available from animal sources, so vegetarians and vegans are advised to eat foods fortified with this vitamin (such as tofu fortified with B12, or certain bran breakfast cereals with added B12) or take supplements in pill or capsule form. Vegetarian sources of vitamin B12 such as seaweed are not as ‘bio-available’ as vitamin B from animal sources, meaning that you would need to eat a large quantity to get enough for your body’s needs.

The best sources of vitamin B12 are lamb’s liver, beef liver, canned oil fish  (such as canned sardines, herring or anchovies), mackerel, smoked salmon, cooked clams, crab, and crayfish.

Foods like eggs and lean beef were traditionally thought to be good sources, but it is now known that chicken eggs contain a compound which inhibits vitamin B absorption. However, the vitamin B12  in goose eggs and duck eggs is far more easily absorbed. Beef (with the exception of beef liver)  is not as high in this vital vitamin as the other food sources listed above.

Vitamin B12 deficiency

Three groups of people are most likely to be deficient in this vitamin: alcoholics, the elderly, and strict vegetarians/vegans.

Excess alcohol consumption is highly toxic to the body, and vitamin B12 is destroyed by excess alcohol. In the elderly, the ability to produce gastric acid required to break down proteins is depleted, so the vitamin B12 in food is not absorbed as readily. And strict vegetarians/vegans (like my personal training client in Chelsea) are simply not eating the foods which are rich in readily-absorbed vitamin B12, unless they eat foods which the manufacturers have fortified with B12.

Symptoms of vitamin B12 deficiency

Poor memory, fatigue, depression, body odour, sore tongue, tingling limbs. In extreme cases symptoms include nerve damage, neurological deterioration.

Vitamin B12 deficiency can also trigger pernicious anemia, an auto-immune condition in which the stomach’s parietal cells are destroyed. These cells are responsible for producing ‘intrinsic factor’ which is needed for vitamin B absorption.

As a personal trainer I offer my clients ongoing nutrition advice, and one of the things I look out for when I check the client’s completed nutrition questionnaire is an inadequate consumption of foods rich in readily-absorbed vitamin B12.

Dominic Londesborough is a personal trainer in London who also offers online nutrition coaching.