http://www.diet-and-health.net/Nutrients/Cobalamin.html

A little excerpt from the article:


"...It is for these reasons that B12 deficiency leads to anaemia (blood disorders include macrocytos and pernicious anaemia) and neurological disorders (Alzheimer's disease and suspected amalgam related disorders). There are, as with many diseases, usually more than one factor which may be involved with causation. Given that the former disorders are rare, even in vegans who have low B12 intakes, what I am more concerned about is the potential for neurological disorders that may be subclinical. This occurs because it is possible to have a deficiency of B12 in the CNS even when blood levels of B12 are "normal", or what is called non-anaemic deficiencies. These occur for meat eaters with huge B12 intakes as well as for vegans. So laying the blame for neurological problems on veganism or indeed any alleged B12 intake deficiency is not always accurate, since increased B12 dietary intake will evidently, not always work. In these serious cases B12 is usually injected since dietary availability of B12 can be as low as 1% of the total ingested for mega B12 doses, and some patients do not convert dietary B12 to the methylcobalamin required for normal neurological activity so well.

Symptoms could include: disturbed sense of co-ordination, paraesthesiae, loss of memory, abnormal reflexes, weakness, loss of muscle strength, exhaustion, confusion, low self-confidence, spacticity, incontinence, impaired vision, abnormal gait, frequent need to pass water and psychological deviances. Non-anaemic deficiencies play a role in diseases such as Multiple Sclerosis, Fibromyalgia, Diabetes and Chronic Fatigue Syndrome. Schizophrenia has also been successfully treated with B12 plus other supplements, and cardiovascular disease is linked to B12 deficiency while herpes zoster used to be treated with B12 injections back in the 1950s.

Just as mercury may cause cobalamin deficiency in the nervous system, so alcohol can cause deficiency in tissues. Even worse, alcohol seems to raise serum levels of vitamin B12, so that the deficiency is masked and the subject may look like they have higher than normal B12 levels! Whether these effects correlate to alcohol intake, or are only found in "alcoholics" is not clear."