From http://www.whale.to/w/b12.html :
"VITAMIN B12 LEVELS AND MERCURY - A LINK WITH MULTIPLE SCLEROSIS AND OTHER DISORDERS
Swedish physician and researcher, Dr Britt Ahlrot-Westerlund, working at the Karolinska Institute, has investigated levels of specific nutrients, including vitamin B12, in heavy metal-affected patients (and in particular those with multiple sclerosis), since the early 1970's. She has specifically studied vitamin B12 levels, mainly in heavy metal-affected patients, and has done considerable work with supplementing vitamin B12 by injection in her amalgam damaged patients with many different disorders, particularly those with multiple sclerosis. In an article written in conjunction with Heavy Metal Bulletin Editor, Monica Kauppi, Dr Ahlrot-Westernund explains that the administration of relatively high doses of vitamin B12, in the form of methylcobalamin, in the treatment of fibromyalgia, diabetics, MS and amalgam-related disorders, has been gradually increasing in Sweden since the end of the 1980s. She reports that the results of this treatment are remarkable.
Note: According to the Heavy Metal Bulletin, March 1999, some researchers [including Dr Hal Huggins] and the International Academy of Oral Medicine and Toxicology in the USA have previously recommended caution in the use of methyl cobalamin injections in the treatment of amalgam patients. They feared that vitamin B12 in that form could readily methylate mercury in the body, ie. transform it into its more harmful form of methylmercury - when methylated, mercury is much more easily absorbed to the blood and then transformed to mercury ions, which are an intensely toxic form of mercury.
THE PRESENCE OF MERCURY CAN REDUCE VITAMIN B12
In a joint article in the December 1995 issue of Heavy Metal Bulletin by Dr Ahlrot-Westerlund and Editor, Monica Kauppi, they explain that the presence of heavy metals can reduce the uptake of vitamin B12. "The transport of vitamin B12 to the brain can be disturbed or interrupted by heavy metals such as mercury, which affects the blood-brain barrier by causing leakage and hampering the active transport of nutrients. In regard to heavy metal toxicity, in many cases it can be assumed that multiple deficiencies, not always easily separable, can be found."
"Lately it has been discovered that anaemia is not always present in neurological and psychological disturbances associated with B12 deficiencies. In diseases such as Alzheimer's and suspected amalgam related disorders, hidden B12 deficiencies in the central nervous system (withoutlow blood values) have been found."
"Vitamin B12 deficiencies have been mainly related to blood deficiency diseases such as pernicious anaemia. Low levels of B12 are followed by neurological and psychological disorders, such as 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, frequent need to pass water, and other psychological disturbances."
Dr Ahlrot-Westerlund explained a possible reason for the mercury/B12 connection: "Mercury seems to change valency and binding site in the body, and this causes increased free radical formation. It is possible that the mercury change in valency in pro-oxidative direction, oxidises the cobalt atom in the B12. Due to its molecular size, vitamin B12 normally has difficulties in crossing the blood-brain barrier, and it is possible that denaturation makes this even more difficult." "