Vitamin B12 (Cobalamin) is a water-soluble member of the B vitamin group of nutrients.
The body treats Bl2 differently from other B vitamins, using it at such a low rate that small amounts are stored in the body. Thus, while it is important to include foods that contain B12 in the diet, the body does not require a daily intake of this nutrient, as the way it is absorbed and excreted differs from other water soluble vitamins.
Vitamin B12 is unique among the vitamins because it is not commonly found in plants, only food from animal sources. Liver is the richest natural source, followed by kidney.
Meat – lamb, beef and pork – come next, then fatty fish and to a lesser extent, white fleshed fish and eggs.
Dairy produce such as milk, yoghurt and cheese contain very small amounts, although enough to be of significance if they are consumed on a regular basis.
B12 is also synthesised by the natural bacteria that populate the lower intestine, although this takes place too low down in the gut to be of use to the body.
A substance called intrinsic factor, a glycoprotein, is secreted in the stomach to aid the absorption of B12 from the gastro-intestinal tract. If the intrinsic factor cannot be produced by the body B12 cannot be absorbed. Pernicious anaemia is a disease of malabsorption and needs to be medically diagnosed and treated.
The gastric juices containing intrinsic factor interact with B12 in the presence of calcium and protect it during its journey to the ileum where absorption takes place. Then an intricate process involving calcium allows the vitamin to be absorbed into the mucosal cells.
It is then carried by proteins to be stored, mostly in the liver. In normal adults, between 2 and 5 mg of B12 is stored in the body, over half of which is found in the liver. Some Bl2 is excreted in the bile and is partly reabsorbed by normal healthy people. It is likely that up to 2 mcg daily is excreted in the faeces and less in the urine.
Generally, the nutrient stays intact better than most other B vitamins. Due to its solubility in water, some small vitamin content can be lost in the juices and fluids that leach out of the food during thawing, washing, preparation and cooking.
Any juices that can be collected from the utensils used during cooking meat or offal should be used for gravy or sauce to make full use of their nutrient content.
Recommendations for a daily required amount of Bl2 vary the EU RDA is currently 2.5 mcg but it can be taken is much higher doses without adverse effects.
It is generally thought that daily supplementation of B12 should be considered by people at the highest risk of deficiency such as:
- pregnant and breastfeeding women (especially when vegan)
- vegans, vegetarians and those on unusual diets.
- the elderly
- people who smoke heavily
- people who take medication that suppress gastric acid secretions (as for stomach ulcers).
Although it is true that only a small amount of this unusual vitamin is required to maintain health, a deficiency will affect every cell in the body.
By far the most dangerous outcome of B12 deficiency is the degeneration of nerve fibres in the spinal cord and elsewhere, affecting the whole nervous system.
The most severe effects occur in:
- tissues where rapid cell division takes place
- blood formation
- the lining of the gastro-intestinal tract resulting in anaemia similar to that resulting from folic acid deficiency.
Other symptoms can be:
- smooth, sore tongue
- menstrual disorders
Pigmentation changes of the skin on the hands can also be a symptom in dark-skinned people.
Those most at risk of B12 deficiency are some vegetarians and vegans whose diets contain no milk, eggs or foods of animal origins and is devoid of cobalamins.
Supplements are suitable for vegetarians, being made by fermentation process and should certainly be considered by people who know their diet is lacking in B12.
Other reasons for deficiency can be:
- intestinal parasite (worms)
- old age
- heavy smoking
- non absorption (due to lack of intrinsic factor)
Folic acid is the nutrient most closely linked with vitamin B12 as both nutrients are equally essential to vital functions concerning the formation of red blood cells, the synthesis of constituents of DNA and the prevention of anaemia.
Calcium is needed to ensure efficient absorption of B12 from the bowel.
B12 acts synergistically with other nutrients in the group. It can be taken as part of a general B complex supplement, but in certain conditions, it can be taken as a single supplement.