Vitamin B12, occasionally also known as cobalamin, is one of the most important and most intensively studied of the B complex vitamins. This group of vitamins is known as the B complex because of their biochemical similarity and because of their close interaction and interdependence in the performance of their numerous vital functions. So the B complex vitamins are commonly found together in various common food sources and, each being water soluble, will also be excreted together from the body. A deficiency in one of the complex is therefore almost always accompanied by a corresponding deficiency in each of the others.

But all of that said, the consequences of a deficiency are different in the case of each individual vitamin, and deficiencies of B12 are particularly associated with cardiovascular disease, a type of anaemia, Alzheimer’s disease and other dementias, and depression.

Vitamin B12 is required for the body’s manufacture of the essential amino acid, methionine and its associated enzyme, methionine synthase, an inadequate supply of which may lead to an excess of homocysteine, a naturally occuring protein within the body, which is well known to be associated with an increased risk of cardiovascular disease.

But it is also now known that sufferers from Alzheimer’s disease are often found to have low levels of vitamin B12 in their blood as well as the raised levels of homocysteine which are also associated with more common vascular dementias. In fact a number of studies have suggested that low B12 and high homocysteine levels may as much as double the risk of Alzheimer’s.

Although conventional medicine remains reluctant to accept any causal link, it might well seem to the “intelligent layman” who takes an interest in these matters that such a link is more likely than not. And this is particularly so when it is remembered that vitamin B12 deficiency leads to a reduction in the synthesis of methionine, which is known to be essential for the methylation reactions which are in turn vital for the health of nerve cells and neurotransmitters.

Research has also noted a strong associative link between vitamin B12 deficiency and depression, that widespread and disabling, but still poorly understood and defined condition. In fact different studies have suggested that up to 30% of patients with depression severe enough to require hospital admission may be deficient in vitamin B12, and that elderly people found to be deficient in the vitamin are twice as likely to suffer severe depression as those with normal blood levels.

Again the conventional “wisdom” prefers to regard these findings as an observational association rather than evidence of a causal link. But it has been argued that such a link may be due to B12’s acknowledged role in the synthesis of methionine and its associated enzymes, which are vital for the effective performance of certain neurotransmitters whose absence is known to be a factor in depression.

Evidently Alzheimer’s disease, dementia and depression are all conditions which become more common and more severe with advancing age, so perhaps it should be no surprise that deficiencies of vitamin B12 are also much more frequent in the elderly population. In fact as many as 10 -15% of the over 60s may be severely deficient, but a far higher proportion than this are likely to fall below the threshold required for optimum protection against these justifiably dreaded diseases.

However, these deficiencies are unlikely to be caused by an inadequate dietary supply. The Recommended Dietary Allowance (RDA) for vitamin B12 is only 2.4 mcg a day, an amount which should be readily obtainable, except perhaps for those following a strict vegetarian regime, given that a single 3 oz serving of fish or red meat may provide this quantity. For those with a taste for it, sea food may provide a great deal more, and chicken, turkey, eggs, milk and cheese are also useful, though less lavish, sources.

But good absorption of vitamin B12 from food is heavily dependent on the normal stomach acid and digestive enzymes, the quantity and effectiveness of which decreases substantially as the body ages, and on the presence in the stomach of a specialised protein known as Intrinsic Factor. The correct action of Intrinsic Factor requires the presence of adequate calcium in the body, another nutrient in which the elderly are of course notoriously likely to be deficient.

Absorption of B12 from supplements is much less problematic, however, because stomach acid and digestive enzymes are not required to release the vitamin from its protein bindings. So this is a rare case in which even conventional medical “wisdom” recognises the value of supplementation, at any rate for the over 50s.

So given that relatively small amounts of these vitamins are required by the body, and that no toxicities or adverse side effects have been reported, there really seems no reason to run the risk of a deficiency.