Dear Dr. Khadavi, Would taking oral zinc supplements in the amount of 30 - 90 milligrams per day be expected to inhibit or to stimulate the 5-alpha reductase types 1 and 2 ? Or, would there be almost no effect at all ?
Dear Dr. Pottkotter,
Thanks for the question, however there has not been a good study on amount of Zinc needed to effect the levels of testosterone or DHT. A study done in the 80's showed low amounts of Zinc supplementation may actually increase DHT production:
Arch Androl. 1981 Aug;7(1):69-73.
Effect of zinc administration on plasma testosterone, dihydrotestosterone, and sperm count. Netter A, Hartoma R, Nahoul K.
The effects of zinc therapy on plasma testosterone (T), dihydrotestosterone (DHT), and sperm count were studied in 37 patients with idiopathic infertility of more than five years duration. In the first group (T less than 4.8 ng/ml; 22 patients), T and DHT rose significantly after oral administration of zinc, as did the sperm count. Nine wives became pregnant, six within 3 months and three within 2 months of a second trial. In the second group (T greater than or equal to 4.8 ng/ml; 15 patients), T and sperm count were unaffected by zinc, while DHT increased significantly. There was no conception observed. The rationale of this treatment and the significance of the results are discussed.
PMID: 7271365 [PubMed - indexed for MEDLINE]
However, when you look at a rat model it appears that you need a large amount of Zinc for body weight and diet to have effects on DHT production. From the study below extrapolated for human weight, you need 2.1 Kilograms of Zinc daily to have an effect on DHT production. But this must be done on humans to really see the dose curve for Zinc-DHT inhibition.
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