Within a regular diet, the only reliable unfortified sources of vitamin B12 are meat, dairy products and eggs. Over the years, some considerable research was done into possible plant food sources of B12. Fermented soya products, seaweeds and algae are among those which were proposed as possible sources of B12, and articles may be found on them. However, as of today, analysis of these fermented soya products, including tempeh, miso, shoyu and tamari, yielded no significant amounts of the vitamin.
Spirulina, a type of algae, and nori, a type of seaweed, which are taken in by some cultures have also both seemed to contain significant amounts of B12 after analysis. Current standpoint however is that these would be B12 analogues. This would mean they are compounds similar in structure to B12 but cannot be used to meet dietary requirements. Bacteria present in the large intestine are also able to synthesize B12. Previous beliefs were that this B12 from these colonic bacteria could be absorbed and then used by the body.
It is known however that the bacteria produce it too far down the intestines to be absorbed for usage. Q2 answer: The reason that the child was anemic is due to the fact that the hematologic manifestation of a deficiency in vitamin B12 is megaloblastic anemia. Megaloblastic anemia is caused by various DNA synthesis defects. In order to understand this, one must know the purpose of folic acid. Folic acid is essential for purine biosynthesis. It is absorbed from the diet, and then is subsequently activated to produce active tetrahydrofolic acid (THF).
This THF form is what is needed for single carbon transfers which take place within the synthesis of pyrimidine nucleotides. An absence or decrease in adequate levels of the active form THF will lead to a deficiency in the ability to repair and replicate DNA. The importance of Vitamin B-12 lies in the fact that it is a cofactor for the activation of folic acid. The absence of vitamin B12 leads to an inability to activate folic acid to THF, thus leading to a similar scenario as folic acid deficiency.
There is a reduction in DNA synthesis and the rate of cell production, with an endpoint being pancytopenia. For the cells however that are produced, the effect is an arrest of nuclear maturation, wherein these have immature nuclei relative to the degree of maturation of the cytoplasm. Q3 answer: Yes, the infant was in danger of irreversible CNS damage. In addition to the hematologic manifestations of vitamin B-12 deficiency, other manifestations would be abnormalities of the gastrointestinal tract and nervous system. This is why the underlying cause of megaloblastic anemia must always be determined.
The difference between folic acid deficiency and B12 deficiency is that although both will cause the characteristic megaloblastic anemia, only B12 is associated with neurologic involvement. Thus, if a patient were misdiagnosed as folate-deficient, when the problem is actually an independent or concomitant B12 deficiency, then treatment with folic acid alone will only alleviate the anemic symptom. The danger is that this may aggravate the situation by causing a delay in supplementation with B12 and lead to permanent neurologic damage.
Q4 answer: In humans, there are only two enzymatic reactions that are known to be dependent on vitamin B12. In the first enzymatic reaction, methylmalonic acid is converted to succinyl-CoA using vitamin B12 as a cofactor for the reaction. This is the reason why a deficiency will lead to increased levels of methylmalonic acid. Without B12 as a cofactor, the reaction does not take place and there is a buildup of the unconverted methylmalonic acid in the body. In the second reaction, homocysteine is converted to methionine with the use of both vitamin B12 and folic acid as cofactors.
This is the very step that is essential for the activation of folic acid. Thus, a deficiency in B12 leads to homocysteine buildup as well. Here, we also see an important diagnostic difference between the two nutrient causes of the megaloblastic anemia in that vitamin B12 deficiency causes a high level of both methylmalonic acid and homocysteine, while a folate deficiency will only show an increase in homocysteine. Q5 answer: Yes it is necessary that B12 be given by intramuscular injection to the child.
The reason for this that the cause of the child’s B12 deficiency has yet to be fully investigated and giving it by injection ensures that it is absorbed by the body. Inadequate B12 dietary intake is extremely rare in children. The most common cause in general is pernicious anemia, although this is rare in childhood. In the young, a deficiency of vitamin B12 activity will usually be seen to be caused by intestinal malabsorption or a congenital deficiency of one of the vitamin B12 carrier proteins.
Over current research, it has also been noted to occur in patients with human immunodeficiency virus (HIV) infection, whether or not they have the acquired immunodeficiency syndrome (AIDS). Hence, due to the urgency of the situation in the case, it was imperative that the physicians administer B12 via the injection to ensure absorption, rather than give it orally, wherein if an undiagnosed intestinal absorption defect were present, a further aggravation of the condition would occur.