Monday, December 7, 2009

Peeing out vitamin B12 is related to total urine volume not vitamin B12 intake

Doesn't a title like that make you grateful that you are not a nutritional scientist. Imagine collecting nearly 300, 24hour urine samples. When ever I think I might have a grotty task to do I remember when I went through a local testing laboratory and talked to a women who did the fecal analysis for various compounds!

The background that you should be aware of is that the water soluble vitamins, that is the B family, C, biotin an Choline are pee-ed out of the body in proportion to your daily intake. This is because the body has very little storage, so the theory is that any vitamin intake above what your body needs is removed into the urine. Now this is only partially true. Because as you increase your dose of these water soluble vitamins your urine level does increase. However your retention also increases. However most nutritional experts will point to the increase in urine output and say that this shows you don't need that level of water soluble vitamin. However what they don't tell you is that your intake and use also went up with the increased dose.

Well it appears that vitamin B12 in urine is not increased by increasing intake. Furthermore the removal of vitamin B12 from the body is related to the total urine produced. This mean that the more you pee the more you loose.

Now this study was done in both young women and elderly women in Japan so it might not apply to you. However I suspect it would be the same across cultures. Also the dose of the vitamin was 1.5mg. This is a high dose the RDI for vitamin B12 is 6 micro grams, or 0.006mg, so 1.5mg is about 500 times larger. (it was a once off dose)

How much did the urinary extrication go up by - only by 30%! This tells me that an intake of 6 micro grams, the RDI, is no enough to supply what your body needs.

Yet another study that shows our RDI's are not giving our bodies what they need.

Reference: Urinary excretion of vitamin B12 depends on urine volume in Japanese female university students and elderly Nutrition Research. Volume 29, Issue 12, December 2009, Pages 839-845

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