Dangers of b12

[Alfabeta]

I read this on web MD - is it correct?

Vitamin B12 is LIKELY SAFE for most people when taken by mouth, applied to the skin, taken through the nose, administered as a shot, or injected into the vein (by IV). Vitamin B12 is considered safe, even in large doses.

Mild itching has been reported in one person who used a specific avocado oil plus vitamin B12 cream for psoriasis.

Special Precautions & Warnings:

Pregnancy and breast-feeding: Vitamin B12 is LIKELY SAFE for pregnant or breast-feeding women when taken by mouth in the amounts recommended. The recommended amount for pregnant women is 2.6 mcg per day. Breast-feeding women should take no more than 2.8 mcg per day. Don't take larger amounts. The safety of larger amounts is unknown.

Post-surgical stent placement: Avoid using a combination of vitamin B12, folate, and vitamin B6 after receiving a coronary stent. This combination may increase the risk of blood vessel narrowing.

Allergy or sensitivity to cobalt or cobalamin: Do not use vitamin B12 if you have this condition.

Leber's disease, a hereditary eye disease: Do not take vitamin B12 if you have this disease. It can seriously harm the optic nerve, which might lead to blindness.

Abnormal red blood cells (megaloblastic anemia): Megaloblastic anemia is sometimes corrected by treatment with vitamin B12. However, this can have very serious side effects. Don't attempt vitamin B12 therapy without close supervision by your healthcare provider.

High numbers of red blood cells (polycythemia vera): The treatment of vitamin B12 deficiency can unmask the symptoms of polycythemia vera.

[helvella]

Leber's disease, a hereditary eye disease: Do not take vitamin B12 if you have this disease. It can seriously harm the optic nerve, which might lead to blindness.

However, several of the few papers about Leber's (LHON) actually suggest taking B12, often in high doses!

I have understood that it is specifically cyanocobalamin that must be avoided because, it is thought, the pathway which converts cynaide into thiocyanate does not operate properly in suffers of LHON.

Leber's hereditary optic neuropathy and vitamin B12 deficiency.

Pott JW1, Wong KH.

Author information

Abstract

BACKGROUND:

Leber's hereditary optic neuropathy (LHON) is a maternally inherited optic neuropathy caused by mutations in mitochondrial DNA (mtDNA). It is also believed that several epigenetic factors have an influence on the development of LHON.

METHODS:

A case series was observed.

RESULTS:

Three patients who developed bilateral optic neuropathy are presented. All patients had a primary LHON mutation in their mtDNA, but also a subnormal vitamin B12 serum level at the time of presentation.

CONCLUSIONS:

The clinical picture of optic neuropathy associated with vitamin B12 deficiency shows similarity to that of LHON. Both involve the nerve fibres of the papillomacular bundle. The present case reports suggest that optic neuropathy in patients carrying a primary LHON mtDNA mutation may be precipitated by vitamin B12 deficiency. Therefore, known carriers should take care to have an adequate dietary intake of vitamin B12 and malabsorption syndromes like those occurring in familial pernicious anaemia or after gastric surgery should be excluded.

ncbi.nlm.nih.gov/pubmed/165...

But I also think that there is much that is still unknown about LHON.

[Gambit62 Administrator in reply to helvella]

WebMD - presumably US site - and there is a lot of confusion because of the assumption that the only available form of B12 in US is going to be cyanocobalamin.

The warnings relating to pregnancy are phrased as being based on caution rather than evidence - and there is a lot that isn't known about effects of almost everything in relation to pregnancy and breast feeding.

Without seeing the actual article its difficult to understand what the actual scope of the warnings is (ie whether it is aimed at people who are B12 deficient through diet or people who have a B12 absorption problem). It is unspecific about doses (particularly in relation to the comment on treatment post stent surgery)

Basic advice would be for people without absorption problems to consult with a health care professional before supplementing ... and for anyone who has a medical condition to ensure that they disclose all medications AND supplements when discussing issues with health care professionals when discussing treatment.

[Alfabeta in reply to Gambit62]

its ‘web md b12’ put that in and it gives an overview of b12. I was concerned about what it was saying about red blood corpuscles and the importance of only taking the vitamin under health care supervision.

[Frenchiebabe]

Pts often receive injected B12 due to malabsorption so by mouth would be of no benefit -