ZMA supplement: what zinc, magnesium and B6 do to your testosterone

A ZMA supplement does not raise your testosterone if your zinc and magnesium are already fine. In 42 trained men, eight weeks of ZMA changed nothing in total or free testosterone. IGF-1, strength and body composition stayed the same too (Wilborn 2004, PMID 18500945). In 14 exercising men who already ate enough zinc, testosterone stayed flat too (Koehler 2009, PMID 17882141).

What strikes me as a training partner? ZMA is one of the oldest boosters on the market. The story behind it comes from exactly one trial. That trial was the maker's.

Below is what ZMA is and what those three trials measured. Why people take it before sleep, and what you can measure yourself.

What is ZMA?

ZMA stands for zinc monomethionine aspartate, magnesium aspartate and vitamin B6. A typical daily dose contains 30 mg zinc, 450 mg magnesium and 10.5 mg B6. You take it before sleep, on an empty stomach.

So it is not a herb, but a combination of two minerals and a vitamin. That makes the evidence easier to read. Zinc and magnesium are both well studied, independent of the brand.

The formula was developed in the 1990s by Victor Conte's company. The same Conte was later at the centre of the BALCO doping scandal. That says nothing about zinc, but something about the marketing.

What is ZMA good for?

ZMA is good for topping up zinc and magnesium if you are not getting enough. Hard-training athletes lose both minerals through sweat, and a zinc deficiency demonstrably lowers your testosterone. Four young men ate a low-zinc diet for twenty weeks. Their testosterone fell from 39.9 to 10.6 nmol/l (Prasad 1996, PMID 8875519).

Nine older men with a mild zinc deficiency took zinc for three to six months. Their testosterone rose from 8.3 to 16.0 nmol/l. That is a doubling, with a deficiency.

Without a deficiency, nothing happens. That is the whole ZMA literature in one sentence. More on that mechanism is in zinc and testosterone.

The maker's trial against the two independent ones

The only trial that saw a rise appeared in 2000 and was paid for by the maker. In American football players, free testosterone rose by more than 30 percent. Strength increased too (Brilla and Conte 2000). That trial is not in PubMed and has never been repeated with the same result.

Then came two independent trials. Wilborn had 42 trained men take ZMA or a placebo for eight weeks alongside their training. Total testosterone, free testosterone, IGF-1, bench press and leg press did not differ between the groups. That is Wilborn's result (2004, PMID 18500945).

Koehler gave 14 exercising men aged 22 to 33 a high dose of zinc. Their zinc intake was already ample, and the extra zinc mostly left the body in urine. Total and free testosterone in serum did not change (Koehler 2009, PMID 17882141).

Three trials, one rise, and that one had an interest. That is how I read it.

Why take ZMA before sleep?

ZMA is taken before sleep, on an empty stomach. Magnesium plays a role in relaxing muscles and nerves. An empty stomach also improves zinc absorption.

Calcium blocks that absorption. Milk or quark with your ZMA is therefore a bad idea.

Whether ZMA actually improves your sleep has never been properly measured. With a magnesium deficiency, topping up can help sleep. Without a deficiency the evidence is thin. How magnesium and sleep relate is in magnesium for athletes.

Is it fine to take magnesium together with zinc?

Taking zinc and magnesium together is not a problem in itself. But the zinc dose in ZMA is high.

EFSA sets 25 mg of zinc a day as the safe upper limit for adults. The 30 mg in a ZMA dose is already above that. Many men take a multivitamin with zinc on top.

Too much zinc lowers your copper over time, and with it your immune function. For B6, EFSA set the upper limit at 12 mg a day in 2023. The 10.5 mg in ZMA sits just under it. Add a B-complex and you are over, and too much B6 can cause nerve complaints.

The Dutch Voedingscentrum keeps it simple. People who eat a healthy, varied diet do not need supplements as a rule. That goes for zinc and magnesium too, unless a measurement says otherwise.

What to measure before you start on ZMA

Imagine you are 31 and you train five times a week. You sweat a lot and you eat little meat. Then a zinc deficiency is not far-fetched, and ZMA might be worth it. But you only know that after a measurement.

Zinc, magnesium and cortisol are measured separately via the biomarker pages. Total testosterone, free testosterone and SHBG come together in the hormone panel. For total testosterone alone, the testosterone test is enough.

Measure your zinc and magnesium first, and you know which row you are in. Prasad's, or Wilborn's. That saves a lot of tubs.

What you can do with this

My line: with a deficiency, ZMA is a fine top-up. With enough zinc and magnesium, it is an expensive way to do nothing. The testosterone story comes from one trial with an interest.

How the other boosters fare against the trials is in the overview of testosterone supplements. If you want something for your sleep, read what poor sleep does to your hormones. That is where the bigger lever is.

If a value is off, discuss it with your GP and mention which supplements you take. Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.

References

• Wilborn CD, Kerksick CM, Campbell BI, et al. Effects of zinc magnesium aspartate (ZMA) supplementation on training adaptations and markers of anabolism and catabolism. J Int Soc Sports Nutr. 2004 (PMID 18500945).
• Koehler K, Parr MK, Geyer H, Mester J, Schänzer W. Serum testosterone and urinary excretion of steroid hormone metabolites after administration of a high-dose zinc supplement. Eur J Clin Nutr. 2009 (PMID 17882141).
• Prasad AS, Mantzoros CS, Beck FW, et al. Zinc status and serum testosterone levels of healthy adults. Nutrition. 1996 (PMID 8875519).
• Brilla LR, Conte V. Effects of a novel zinc-magnesium formulation on hormones and strength. J Exerc Physiol Online. 2000;3(4):26-36.
• EFSA. Scientific opinion on the tolerable upper intake level for vitamin B6. EFSA Journal. 2023.
• EFSA. Tolerable upper intake levels for vitamins and minerals: zinc. 2006.
• Voedingscentrum. Voedingssupplementen. voedingscentrum.nl.