Men who take nutritional supplements to help prevent prostate disease need to be aware that some supplements may contain much less or much more of the ingredient than stated on the label, according to a report in The Journal of Urology (Vol. 168: 150-154).

"The take-home message here for consumers of these supplements is buyer beware," said Neil E. Fleshner, MD, head of urology at the University Health Network at the University of Toronto in Ontario.

Fleshner and colleagues bought at stores several different kinds of vitamins and other supplements popular among men interested in preventing prostate disease, including prostate cancer.

The researchers' independent testing showed the seven brands of vitamin E they bought had anywhere from a little more than half the dose stated on the bottle, to above 50% more than the labeled dose.

The selenium they tested ranged from one-fifth less than the labeled dose, to almost a quarter more.

Lycopene supplements ranged from about two-thirds of the labeled dose, to almost one and a half times more than the dose on the label.

One brand of saw palmetto had less than 3% of the dose stated on the label, and another had 40% more than the label said.

Most vitamin D was within 15% of the doses stated on the bottle.

In addition, pill doses varied between lot numbers of the same brand for some supplements.

Even though none of the substances studied has been proven to help prevent cancer, there is some preliminary evidence suggesting vitamin E, selenium, vitamin D, and lycopene might help prevent prostate cancer, Fleshner said.

And there is ample evidence that saw palmetto can help prevent some lower urinary tract symptoms.

But only carefully controlled clinical trials can show whether those supplements really have any benefit, said the Cleveland Clinic's Eric Klein, MD, in an accompanying editorial.

Fleshner agrees, and noted many trials are underway, including some at his institution.

But he says some men take supplements outside of clinical trials to make sure they don't get a placebo (inactive substance used for comparison in trials).

At present, dietary supplements are not regulated by the US Food and Drug Administration (FDA), which means their manufacturers do not have to prove they are safe or effective, or even that they contain what is stated on the label. Regulation to ensure consistent doses and accurate labeling is necessary, because without it men taking the pills may miss out on any benefits such supplements might have, said Fleshner.

Or the men could have side effects from getting too much of a supplement. These could include an increased risk of bleeding from too much vitamin E if they are taking a blood thinner, or side effects from high doses of selenium or vitamin D labeled as lower doses, he noted.

Certification of accurate labeling could be done by the FDA, or by doctors' organizations, such as the American Urological Association, said Fleshner.

Until such certification is available, it's important for consumers to try to seek out accurately labeled brands, perhaps with their doctors' help, he added.

Patients should tell doctors what supplements they are using, because of the potential for side effects and because some may interfere with therapy, said Fleshner.

And more doctors need to educate themselves about the known risks and benefits of various nutritional and herbal supplement products, rather than tuning out the topic, Fleshner said.

Brooks agreed with Klein on the need for continued clinical trials.

And he endorsed Fleshner's call for consumer caution, and for regulation.

"If these substances are going to be touted as having anti-cancer properties, maybe it's time for the FDA or some other regulatory body to step in and begin to look at just what's being sold to the public," said Brooks.