Zinc is classified as a trace mineral, but its physiological functions are far from minor. It is required for the activity of over 300 enzymatic reactions, the function of over 2,000 transcription factors that regulate gene expression, the structural integrity of protein hormones and receptors, and the maintenance of cell membrane integrity. It is concentrated in the testes and prostate in men, in immune cells in both sexes, and in the hippocampus of the brain.
Zinc and Testosterone
Zinc is required for the function of the enzyme 5-alpha reductase that converts testosterone to the more potent dihydrotestosterone, and for the Leydig cell enzyme systems that produce testosterone from cholesterol. A placebo-controlled trial found that zinc supplementation in men with marginal zinc deficiency produced significant increases in serum testosterone after six months. Conversely, dietary zinc restriction in young men reduced serum testosterone by 75 percent over 20 weeks, demonstrating the strong dependence of testosterone production on zinc status.
Best Dietary Zinc Sources
- Oysters: by far the richest food source at 74mg per 100g; a single oyster provides more than the daily requirement
- Beef: 4 to 5mg per 100g from lean cuts; haem zinc is significantly more bioavailable than plant zinc
- Pumpkin seeds: 7.5mg per 100g; the best plant source; soak briefly to reduce phytate that inhibits absorption
- Crab and prawns: 3 to 4mg per 100g
- Legumes: 1 to 2mg per 100g cooked; bioavailability improved by sprouting or soaking
- Note that plant-based zinc has lower bioavailability due to phytate binding; vegans and vegetarians should target the upper end of the recommended intake range