Zinc: the ceiling, the copper problem, and the ZMA story

Zinc is the quiet one. No influencer sells it, nobody makes a video about it, and it sits in the corner of the stack doing work that only becomes visible when it stops. It is also the one where taking more than you need creates a second deficiency you were not looking for.

And it is the mineral behind the most instructive supplement story in this sport, which is what happened to ZMA.

Why a fight camp drains it

Zinc leaves in sweat, and a study of active men found training depletes stores faster than an ordinary diet replaces them. That is the baseline problem before a camp adds anything to it.

Then the camp adds two things. Energy restriction cuts total intake of everything, and the foods richest in zinc are meat and seafood, which are exactly the foods that shrink first when a fighter starts managing weight. And a plant-based fighter faces a third problem on top: phytates in grains and legumes bind zinc and can cut absorption substantially, which is why vegetarian requirements are set higher than omnivore ones.

The reference intake for men is 11 mg a day. That is a general-population figure for somebody who is not sweating through 2 sessions daily on restricted food.

The copper problem

This is the part that is missing from almost every label, and it is the reason the upper limit exists.

Zinc and copper compete for the same intestinal absorption route. Push zinc up and copper absorption goes down, and the body responds to a high zinc load by producing more metallothionein, a protein that binds copper and keeps it from being absorbed at all.

Do that for weeks or months and you produce a copper deficiency. Copper is required for iron metabolism, so the consequences include anaemia, and in more severe cases neurological symptoms and impaired immune function.

The irony is complete: you took zinc for your immune system and ended up compromising it through a different route.

The ceiling, and the study everyone in wrestling quotes

The tolerable upper intake level for zinc is 40 mg a day of elemental zinc, from all sources including your multivitamin. Above that chronically, the copper story starts.

Now, the study that gets cited whenever combat sports and zinc come up. A 2006 trial in elite wrestlers gave zinc sulfate at 3 mg per kilogram of body weight daily for 4 weeks and reported that resting and post-exercise testosterone were higher afterwards, and that the usual exercise-induced fall in thyroid hormones and testosterone was blunted.

Work out that dose carefully, because it is easy to get wrong and I did on the first pass. Three milligrams per kilogram for an 80-kilogram wrestler is 240 mg a day of zinc sulfate, not of zinc. Zinc sulfate is only about 23 percent elemental zinc, so the actual zinc dose was somewhere around 55 mg a day.

That is well short of 6 times the upper limit, and still above it by a meaningful margin, sustained for 4 weeks.

So the study most often used to justify zinc in combat sports used a dose no fighter should run through a camp. It is interesting mechanistically.

It is not a protocol, and treating it as one is how people end up copper deficient.

Testosterone, honestly

The pattern here is the same one that appears with vitamin D, and it applies as a general rule rather than a fact about one mineral.

Zinc is a cofactor in testosterone synthesis. Deficiency reliably suppresses production: a landmark experiment restricting zinc in healthy young men produced a large fall in testosterone, and supplementation restored it. That part is solid.

In men who are already zinc-replete, supplementing further does not push testosterone above normal. There is a ceiling, and it is the point at which you are no longer deficient.

Which means the honest question is "am I short of zinc", ahead of "does zinc raise testosterone". For a fighter deep in a camp on restricted food, sweating twice a day, the answer might genuinely be yes. For a well-fed athlete eating red meat and seafood regularly, probably not, and no amount of extra capsules will change the number.

What happened to ZMA

ZMA is zinc, magnesium and vitamin B6, sold as a night-time recovery and testosterone stack. It is one of the most successful supplement products ever aimed at athletes, and its story is the cleanest illustration I know of why funding matters.

The consensus that followed is that ZMA does not raise testosterone in well-nourished athletes. The original number is still quoted in marketing a quarter of a century later.

Form, and the absorption clash

Zinc oxide is the cheap option and absorption is poor, in the region of 10 to 15 percent. Chelated forms are better: picolinate, bisglycinate and citrate all absorb well.

Two rules about when to take it, and the second one contradicts something I have published.

• With food. Zinc on an empty stomach causes nausea reliably enough that it is the main reason people abandon it.
• Separately from iron, and preferably from magnesium. The competition with iron and calcium is well established. With magnesium it is weaker: it shows up clearly at very high zinc doses and is minor at the 15 to 30 mg range. Two hours apart costs nothing, so I separate them, but this is prudence rather than a rule.

In a weight cut

Zinc stays through camp and into the transition phase of the cut, then stops with everything else as the final days close in. It is not one of the three things that survive the last 48 hours, and it does not need to be.

It comes back in the hours after the scale, alongside omega-3, with the second full meal rather than the first. The first meal after a cut has other work to do, and minerals on a shrunken stomach are a way to feel sick during the one window where eating actually matters.

The full sequence is in the rehydration article.

Zinc and colds, honestly

Zinc is sold mainly as a cold remedy, so the evidence deserves a straight answer. A 2024 Cochrane review pooled the placebo-controlled trials. Taking zinc to prevent colds made little or no difference. Taken once a cold had started, it may shorten it by a little over two days on average, but the certainty was low and the trials disagreed widely. It also probably increased minor side effects.

For a fighter that is a weak reason to keep zinc in the bag all year, and it makes a short course at the first sign of a cold a judgement call rather than a protocol. The copper problem above applies either way.

Where a fighter should actually get it

Oysters carry more zinc than anything else by a wide margin. Red meat does the job without the theatre, and a fighter eating beef regularly is unlikely to be short.

That is the uncomfortable part of the food-first argument in this sport. The best zinc sources are the foods that get cut, and the phase when you need zinc most is the phase when they leave the plate. A supplement is a reasonable answer to that specific problem, and it is a poor answer to a diet that never contained the food in the first place.

The version I would give a fighter in one line

Twenty milligrams with dinner, copper if you are on it for months, magnesium later in the evening, and no expectations about your testosterone unless a blood test has told you something.

Everything else in this article exists because somebody sold a fighter the opposite of that sentence, at 40 milligrams a serving, with a number from a study the manufacturer paid for.

The other foundation supplement where timing decides whether it works at all is collagen.