Sources of vitamin B12
Vitamin B12 cannot be made by the body and therefore needs be consumed in the food we eat. As vitamin B12 is mostly found in foods from the animal kingdom, it is important to ensure that the diet contains sufficient animal based food sources to meet our requirements. Vitamin B12 on the other hand is rarely found in vegetable based foods. Supply of this vitamin cannot therefore be guaranteed in those who choose to eat a vegan or a vegetarian based diet.
Since the amount of vitamin B12 differs greatly in different animal food sources, it can still be challenging to achieve the recommended daily intake, even when eating a variety of foods.
On average, we require between 1- 4 micrograms of this vitamin daily, depending on age, nutritional needs and current health to ensure that our energy metabolism and nervous system are working properly. This level varies between children, adolescents, adults, and pregnant or lactating women. The richest sources of B12 are found in beef and calf's liver. Following this the most concentrated sources are lean beef and other muscle meats. Fish sources such as herring, salmon and shellfish are also considered to be good sources. Although present in significantly smaller quantities, eggs and dairy products also provide us with a source of B12.
Uptake of Vitamin B 12 in the Body
Vitamin B12 is absorbed both actively and passively in the body. Active absorption is by far the main way in which B12 is taken up and relies on the presence of a protein molecule called intrinsic factor. Intrinsic factor is produced by the parietal cells of the stomach and it is here, in the stomach that the intrinsic factor binds to the B12. A healthy stomach lining is therefore essential for this process. In this bound form, vitamin B12 is protected on its journey through the stomach and duodenum. Finally both the B12 and its transport molecule are absorbed in the small intestine and first becomes available to the body. B12 can be absorbed to a much lesser extent passively across the gut cell membrane by passive diffusion. This inefficient type of absorption may be useful in circumstances where the parietal cells, which are present in the stomach walls, have become damaged.
Causes of B12 deficiency
A common reason for an inadequate supply of B12 is an inappropriate diet. On a purely vegan diet, where all animal based foods are avoided, the body will not supplied with the vitamin B12 it requires. Without food supplements, the body would be unable to reach its daily requirement for B12. With a vegetarian diet, where meat and fish are avoided, particular attention must be paid to the inclusion of eggs and dairy products.
Irrespective of eating habits, there are also so-called functional and malabsorption disorders of the gastrointestinal tract which can be responsible for B12 deficiency. In this case, the vitamin may not be completely absorbed and utlilised. The reasons for this are diverse and range from gastritis, liver disease, diabetes, alcohol abuse or as a side effects of certain drugs. B12 deficiency can also be caused by a serious autoimmune condition called pernicious anaemia, whereby the parietal cells in the stomach become damaged and are unable to produce intrinsic factor.
Symptoms of vitamin B12 deficiency
The symptoms of vitamin B12 deficiency can be very diverse. This vitamin is involved in a variety of bodily processes, including blood formation, nerve function, energy metabolism and cell maturation and division, therefore the symptoms can be equally as extensive. Examples of vitamin B12 deficiency symptoms include tiredness and fatigue, paresthesia of the extremities (e.g. tingling), lack of drive, and muscle weakness. There may be additional neurological symptoms, including depression, psychosis, memory loss and apathy. In most cases, the symptoms are non-specific, meaning that vitamin B12 deficiency is often overlooked and difficult to diagnose. It also can take many years of deficiency before symptoms become noticeable.
Diagnosis of B12 deficiency is achieved through a blood test and more specifically with the ‘Schilling test’. In this test radiolabelled B12 is administered orally and can be used to detect malabsorption and pernicious anaemia. The presence of the radiolabelled B12 in the urine identifies the exact amount of B12 that has evaded absorption in the intestine. Early detection is always best as at this stage the symptoms are mostly reversible. Long term, untreated vitamin B12 deficiency can lead to serious complications, including paralysis, anaemia, myocardial infarction, stroke and infertility.
B12 supplements are widely available in both tablet and liquid form, either as cobalamin or the more active methylcobalamin. Many practitioners recommend taking B12 alongside the other B vitamins as the work closely together in the body.