Almost the whole zinc and testosterone idea rests on thirteen men
One 1996 paper carries almost the whole idea: four young men had zinc restricted, nine elderly men were given it. Neither arm had a control group or blinding.
What the study found
The zinc and testosterone belief traces back to thirteen men
One 1996 paper carries almost the whole idea. Four young men had zinc restricted and their testosterone fell; nine elderly men already short of zinc were given it and theirs rose. Neither arm had a control group or blinding, and no man in either started with normal zinc.
The caveat · The 73% fall is an anomaly
The restriction arm reported a 73% fall in testosterone from what the paper itself calls marginal restriction, larger than the controlled feeding study found at a far lower intake, which is an anomaly rather than a detail. The supplementation arm recruited men already identified as zinc deficient, so it cannot speak to anyone else. Alongside both sits a correlation measured in 40 men, and a correlation in 40 people is where this began.
What we don't know
The restriction arm reported a 73% fall in testosterone from what the paper itself calls marginal restriction, larger than the controlled feeding study found at a far lower intake, which is an anomaly rather than a detail. The supplementation arm recruited men already identified as zinc deficient, so it cannot speak to anyone else. Alongside both sits a correlation measured in 40 men, and a correlation in 40 people is where this began.