Methylcobalamin vs cyanocobalamin excretion

[Guest guest]

Dinah

I've done a bit of research, and wanted to report on what I've found so far. It is an interesting subject, so I'll continue exploring.

http://en.wikipedia.org/wiki/Vitamin_B12 has a good discussion on methylcobalamin and cyanocobalamin. The body takes cyanocobalamin and converts it to methylcobalamin and adenosylcobalamin, leaving behind the cyanide (miniscule amount).

An additional wikipedia article on methylcobalamin says that one study suggests that methylcobalamin is better retained in the body. Which implies that more cyanocabalamin is excreted than absorbed, perhaps.

The wikipedia article I cited above goes on to say that for those patients who lack the intrinsic factor to absorb B12, there is 80-100% excretion of oral doses in the feces vs 30-60% excretion in feces in individuals who have adequate intrinsic factor. I didn't find a discussion of the excretion factor from serum injections, or which form of B12 serum is better absorbed. Or if there is difference in urinary or feces excretion levels. So I'll keep looking.

Here's a quote from the wikipedia article discussing how much B12 is excreted per day:

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"The total amount of vitamin B12 stored in body is about 2,000-5,000 mcg in adults. Around 50% of this is stored in the liver. Approximately 0.1% of this is lost per day by secretions into the gut as not all these secretions are reabsorbed. Bile is the main form of B12 excretion, however, most of the B12 that is secreted in the bile is recycled via enterohepatic circulation. Due to the extremely efficient enterohepatic circulation of B12, the liver can store several years’ worth of vitamin B12; therefore, nutritional deficiency of this vitamin is rare. How fast B12 levels change depends on the balance between how much B12 is obtained from the diet, how much is secreted and how much is absorbed. B12 deficiency may arise in a year if initial stores are low and genetic factors unfavourable or may not appear for decades."

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In another article abstract on PubMed, a study of urinary excretion in 30 patients given cyanocobalamin injections indicated that there was a wide variation in the amounts excreted and a wide variation in the capacity of tissues to retain injected cyanocobalamin.

There is a lot more research to come. This is enough for now, though [grin].

Kim M.

I cannot determine if the Methylcobalamin is stored as is the cyanocobalamin or is it excreted. Do either of you know? Thank you...Dinah