Short answer: Only, it seems, in men who are short on zinc. In a 1996 study, cutting zinc from the diet of 4 young men lowered their testosterone, and giving zinc to 9 older men who were marginally low raised it. In 14 exercising men who already ate enough zinc, the high-dose zinc product ZMA did not change testosterone. NIH lists 40 mg a day as the adult upper limit and warns that 50 mg or more for weeks can lower copper.
Zinc is needed by hundreds of enzymes. The 1996 study by Prasad and colleagues notes that severe and moderate zinc deficiency is linked with hypogonadism, meaning low testosterone, in men. It then looked at milder shortfalls in three ways:
These were very small groups with no placebo, so they show that zinc matters when it runs short, not that extra zinc raises testosterone in men with enough.
ZMA is a supplement that combines zinc, magnesium and vitamin B6 and is often sold for testosterone. A 2009 study gave it to 14 healthy men aged 22 to 33 who exercised regularly and already took in 11.9 to 23.2 mg of zinc a day from food. Their blood zinc went up, but total and free testosterone did not change, and neither did the testosterone breakdown products in their urine. The authors concluded that ZMA had no meaningful effect on testosterone in people eating a zinc-sufficient diet.
The NIH Office of Dietary Supplements (ODS) puts the recommended amount for adult men at 11 mg a day. Meat, fish and seafood, especially oysters, are the richest sources; zinc from beans and grains is absorbed less well.
ODS says excess zinc can cause nausea, dizziness, headaches, stomach upset, vomiting and loss of appetite. It says doses of 50 mg or more over weeks can block copper absorption, reduce immune function and lower HDL ("good") cholesterol, and sets the adult upper limit at 40 mg a day from all sources. ODS notes that some denture adhesive creams contain zinc, and cites case reports of copper deficiency linked to them.
Zinc also binds some antibiotics in the gut. See minerals and antibiotics for the timing ODS gives.
For a man on testosterone therapy, the testosterone level comes from the dose and schedule, not from zinc. Zinc is still part of a normal diet. Dose Track can log a zinc supplement alongside injections and lab dates, which makes it easy to show the prescriber the full list of what is being taken.
Read more on Dose Track: Zinc · Copper · Low testosterone · Free testosterone