Monday, December 6, 2010

Absurd: Will Supplemental Zinc Gluconate Deplete Your Zinc Levels?

Normally, I restrict myself to very recent studies, but the results of this 2007 (Tompkins. 2007) study on the bioavailability of zinc-enriched yeast and zinc gluconate in healthy volunteers that recently resurfaced on the Mind&Muscle boards, is too counter-intuitive and, if not scientifically flawed, important not to make it into the news.

In the study, which used a randomized, two-way crossover design, the volunteers were randomly assigned in groups of three to consume a single dose of either 20 mg of total Zn in the form of Zn gluconate or Zn yeast with 150 ml of water, after that urine, blood, and fecal samples were collected and analyzed over a 48-h period. The results were surprising, while "Zinc gluconate gave higher Zn concentrations in the blood in the first 6 h" it did not only show greater loss in the feces, but ...
the net Zn balance after 48 h for Zn yeast was 9.46 but for Zn gluconate it was -2.00, indicating that Zn gluconate supplementation contributed to a net loss of Zn.
As far as the reasons for this observations are concerned, the scientists speculate:
Presumably, this “extra” Zn lost was released from the body’s store of Zn metallothionein; however, we do not have any evidence of the source of the Zn material. This may suggest that the Zn salts stimulated a Zn detoxification pathway.
If this were true and the results are not biased by the background of the Institut Rosell, which is obviously financed by Lallemand Inc. who produce (pro-)biotic products (i.e. yeast based products), you might want to reconsider your own supplementation practices. The high doses of Zn Salts commonly used by bodybuilders and fitness enthusiasts (many suggest >50mg Zinc per day) may in fact lead your body to believe he becomes intoxicated with zinc. It is then a very natural reaction to excrete zinc and as the data from this study shows, this "excess" zinc (i.e. more zinc than you supplied) must - at least in parts - stem from zinc stores somewhere in your body.