Zinc, a BodyBuilder's Favorite Mineral: All That Glitters is not Gold

I know, you think you can hardly get enough Zinc and have to supplement 30mg+ of zinc in the form of highly bio-available (and expensive) supplements. Right? Have you ever thought about side effects besides reducing estrogen? No? Then you should have a look at a recent study by Brazilian scientists (Marques. 2010).

Figure 1: Zinc supplements
are a bodybuilder's favorites

By supplementing only 22mg zinc-gluconate per day over 30 days, the plasma copper levels of 7 trained cyclists decreased and remained low 30 days after cessation. While supplementation had no effect on thyroid metabolism, the scientists made another disquieting discovery:

Fasting serum insulin and HOMA2-IR increased (27% and 47%, respectively) on day 60 compared to baseline (p = 0.03), suggesting a delayed effect of zinc supplementation. Moreover, plasma zinc was positively associated with serum insulin (r = 0.87, p = 0.009) and HOMA2-IR (r = 0.81, p = 0.03) after zinc supplementation (day 30), indicating that supplemental zinc may impair glucose utilization in cyclists.

If this happens in endurance athletes, in bodybuilders, who are always scared they'd lose muscle if they do cardio, the increase in insulin could become problem. If, in addition, you follow a high carb diet and down a few scoops of a weight gainer every other day, you are probably in for trouble. So better keep your zinc supplementation within reasonable limits; plus, if in doubt leave it out ;-)