The study, presented Wednesday at the annual meeting of the American Urological Association in San Diego, aimed to find out how many infertile men take the supplements despite the risks.
The researchers examined medical records of more than 1,500 men with an average age of 35 who sought fertility treatment at the two clinics.
Seven percent of the men were taking supplemental testosterone prescribed by a physician. The study focused on 34 men who agreed to stop using the hormone supplements.
Overall, the sperm counts of most patients bounced back. Average sperm concentration in semen jumped from 1.8 million per milliliter to 34 million per milliliter after supplemental testosterone was discontinued.
But the sperm counts of six of the 34 patients didn't recover. Testosterone treatments normally don't hurt fertility permanently, and it's not clear if they played a role in the men's continued infertility. The study also did not prove a direct cause-and-effect relationship between testosterone supplements and lowered sperm count.
Anawalt said it typically takes between one and six months for a man's sperm count to recover after he stops using a testosterone supplement.
Kolettis, the study co-author, said certain men should avoid testosterone supplements. "I tell men not to take it until they're done having their own biological children," he said.
The supplemental testosterone in question is prescription-only, and unrelated to over-the-counter supplements marketed to increase testosterone production.
Data and conclusions presented at meetings should be considered preliminary until published in a peer-reviewed medical journal.
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