Thursday, September 10, 2009

Selenium bioavailability

As I have mentioned before metals have increasing bioavailability from oxide(s) to salt(s) to metals bound to protein, amino acids or other biological compounds.

Selenium is no different. There at at least three different types of selenium oxide. Two of these types (SeO3 and SeO4) were studied for their bioavailability in adult men. This was undertaken to determine if any differences in selenium oxided in baby formula. This has the assumption that babies absorb selenium like adults, which I know is not true for some compounds.

They found no difference in the retention of selenium in either source, there was 41 and 46%. selenium retention. What is interesting is that one of the selenium oxides (SeO4) was absorbed at a significantly high level of 91% absorption vs 50% absorption. It has been shown in animal studies that the SeO4 selenium oxide was actively transported across the intestinal walls, where as SeO3 selenium passively diffused over the walls and had a tendency to get stuck trying to go through the intestinal wall.

And as stated above we would expect the organically bound selenium to be more useful to the body. Studies have shown that Se-rich yeast or selenomethionine (selenium bound to a amino acid, which is a small bit of protein) have a retention rate of 89-90%.

There is no difference between selenium salts an organically bound selenium and creation of the GSH-Px enzyme (more on this later) . However organically bound selenium results in high plasma and red blood cell selenium levels.

In summary I would like to ask a questions:
  • Why are we feeding our babies the best form of selenium, we feed then substances that they can't use?
  • What type of selenium in your supplement are you taking? If you have any questions about reading your supplement label please email me or leave a comment.
  • Are you using a fertilizer or additive in your garden that contains selenium? I live in NZ were it is well known to have selenium deficient soils and it is proving challenging to find such a fertilizer that I can purchase in smaller than a truck load!
Reference: Peter Van Dael c1, Lena Davidsson †, Rafael Muñoz-Boxa1, Laurent B. Faya1 and Denis Barclaya Selenium absorption and retention from a selenite- or selenate-fortified milk-based formula in men measured by a stable-isotope technique. British Journal of Nutrition (2001), 85:157-163 Cambridge University Press

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