But only 12% of the products contained any ingredient shown to provide some testosterone-related benefit in human trials. And nearly
half (48%) contained ingredients that studies found could have negative
impacts.
"In general, I'm not anti-supplements," noted study author Dr. Mary Samplaski. "I have a lot of patients who take them. But the FDA [U.S.
Food and Drug Administration] says very clearly that these products
should not claim to treat medical conditions. And 90% of these
testosterone supplements do make such claims. So I was just really
curious what the scientific support was for the claims being made."
Samplaski said, "What we found is that in the vast majority of cases there was no evidence to show that any of the ingredients in these
testosterone supplements were effective in any way."
The upshot, she said, is that "people should understand that just because there's a sexy website with a pic of Arnold Schwarzenegger
doesn't mean it's the result they should expect."Samplaski is director
of male infertility with the Keck School of Medicine's department of
urology at the University of Southern California, Los Angeles.To begin
their work, her team googled "testosterone booster," and compiled a list
of the first 50 supplements that came up.
About 90% claimed they would boost testosterone levels. Half claimed to improve libido, and nearly as many claimed to make men stronger.
About 60% promoted building body mass, while 30% claimed to increase
energy, and almost as many were touted as fat burners.
Supplements were then broken down by their ingredients, which included vitamins, minerals, folic acid, mushrooms and a variety of
herbals. Ingredient amounts were also tallied, with an eye towards the
FDA's stated daily allowance and tolerable upper intake levels for each.