Here's a key point that I have found on Wiki:
"In proteins, Zn ions are often coordinated to the amino acid side chains of aspartic acid, glutamic acid, cysteine and histidine.[136] The theoretical and computational description of this zinc binding in proteins (as well as that of other transition metals) is difficult.[136]
There are 2–4 grams of zinc[137] distributed throughout the human body. Most zinc is in the brain, muscle, bones, kidney, and liver, with the highest concentrations in the prostate and parts of the eye.[138] Semen is particularly rich in zinc, which is a key factor in prostate gland function and reproductive organ growth."
I dont think it directly affects test levels though, but I've never really looked into Zinc a whole lot.
Zinc, Testosterone and Men's Health
Zinc is necessary to maintain normal serum testosterone. Inadequate zinc levels prevent the pituitary gland from releasing luteinizing and follicle stimulating hormones, which stimulate testosterone production.
Zinc also inhibits the aromatase enzyme that converts testosterone into excess estrogen. The testosterone to estrogen ratio in men declines with aging from a high of about 50:1 to half of that, or even a low of 10:1. Higher estrogen activity results in increasd risk of heart disease, weight gain, and obesity.
One reason for the progressive weight gain with age is that fat cells contain aromatase. More fat cells mean more estrogen which means more fat deposition.
This is further aggravated by alcohol consumption, which lowers zinc and increases estrogen, and so magnifies the problem.
In addition to the impact on hormone levels, zinc also has been proven to help the body produce healthier sperm by increasing sperm count and motility. A USDA study found that semen volume dropped 30 percent when zinc intake was low. Research published in the American Journal of Clinical Nutrition found that male volunteers who consumed low amounts of zinc exhibited decreased semen volumes and serum testosterone concentrations.
Zinc deficiency has been found to have a severe impact on the male prostate gland. Zinc deficiency predisposes the prostate to infection (prostatis) which may lead to enlargement of the prostate gland (prostatic hypertrophy).