Ask the Expert about ZMA Dietary Supplement

What's the scoop on ZMA? Does it work?

ZMA is a popular new supplement that claims to increase anabolic hormones and strength in athletes. What is the evidence for these claims of improving athletic performance and overall fitness?

How does ZMA work?

ZMA is a combination of two essential dietary minerals (zinc and maganesium) and vitamin B6. Zinc and magnesium are sometimes not adequately supplied in the diet, while vitamin B6 generally is. The zinc is in the chemical forms zinc methionine and aspartate; the magnesium is in the aspartate form.

There is no scientific evidence for any claim that ZMA has any effects beyond those of taking equivalent amounts of zinc, magnesium and vitamin B6 in any other form.

All of these substances are healthy and thus the combination will also be healthy so long as it is not overdosed.

Are there any side effects?

Possible side effects can arise from taking too much (overdosage).

Zinc: More than 50 mg daily often increases the need for dietary copper; more than 100 mg daily might cause toxic symptoms.

Magnesium: More than 1000 mg daily might cause diarrhea.

Vitamin B6: More than 200 mg per day may lead to peripheral neuropathy (nerve pain in the extremities).

What else do I need to know about ZMA?

A study claiming that ZMA increases anabolic hormones and strength in athletes was conducted by L. R. Brilla, Western Washington University, Bellingham, WA, and V. Conte, BALCO Laboratories, Burlingame, CA.

While their results show statistically significant differences between the ZMA and placebo groups following 8 weeks of intensive training (higher testosterone levels and greater increases in strength) -- the study was significantly flawed.

The beginning levels of zinc and magnesium in these athletes' blood were already low. (Average serum zinc was 0.82 mcg/ml; deficiency threshold is 0.7 mcg/ml. Average serum magnesium was 19.6 mcg/dl; deficiency threshold is 16 mcg/dl.)

Increased exercise raises the body's need for zinc in a variety of ways. The fact that levels of zinc and magnesium dropped in the control groups' blood (to 0.8 mcg/ml of zinc and 18.0 mcg/dl of magnesium) shows that the increased exercise had this expected effect.

So both groups needed more of these essential minerals, probably even before the intensive training, but only one group got it.

What happened here can be understood if one thinks about the normal diet eaten by "members of the University football team" (the study's subjects). Their diet is probably low in zinc, magnesium and B6, if not actually deficient -- which is probably true for most unsupplemented people in the US. High protein intake (undoubtedly consumed by these football players) increases the need for B6, and zinc is particularly important for protein (muscle) synthesis.

Further details of Tom's critique of this study, together with abstracts of his own sources of information, can be found on the LEF Forum.