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Despite dietary supplements being popular among prostate cancer patients, a new review of past research says they are not effective treatments for the disease.
Pulling together data from eight randomised controlled trials - considered the gold standard of medical research, researchers found non-herbal dietary supplements and vitamins didn't significantly change the severity of people's cancers.
"The main message would be that no miraculous supplement for (prostate cancer) exists," wrote Dr Paul Posadzki, the review's lead author from the Korea Institute of Oriental Medicine in Daejeon, in an email to Reuters Health.
The American Cancer Society estimates that about 240 000 US men will be diagnosed with prostate cancer in 2013, and about 30 000 will die from it.
According to the researchers, who published their results in the journal Maturitas, it's estimated that between a quarter and three-quarters of patients with prostate cancer take dietary supplements despite limited evidence of any benefit.
Some studies have looked at whether supplements - such as selenium - could prevent cancers, but came up short.
To get a better picture of whether supplements are any good at treating prostate cancer, the researchers reviewed trials that looked at minerals, vitamin D, antioxidants and plant compounds known as isoflavones and phyto-oestrogens.
The researchers had information on 478 prostate cancer patients from eight trials that were conducted in the Netherlands and the US.
The patients' prostate cancers varied across a scale that measures the severity of cancer from 2 to 10 - with 10 being most severe. In each trial, the patients took a supplement - which varied depending on the study - and were tracked for a few weeks or up to five years.
No replacement
Overall, six trials showed that the supplements didn't give patients benefit over patients taking a placebo or another type of supplement.
Two studies did show a significant drop in prostate specific antigen levels - a potential but controversial marker of cancer - among patients taking a combination of supplements, compared to patients taking placebos.
However, neither of those studies included more than 50 people and both were sponsored by supplement manufacturers.
"I do not think these supplement combinations could help and no supplement can replace the balanced diet. By no means is the evidence conclusive," Posadzki said.
Dr Eric Klein, chair of the Glickman Urological and Kidney Institute at the Cleveland Clinic in Ohio, said the new review's findings are consistent with past research.
"I think if you survey the literature on nutritional supplements and cancer, there is almost no evidence that they're helpful. In fact, some people have found that there is evidence of harm," said Klein, who was not involved with the review.
"I think that until we get a better understanding of the biology of how supplements affect normal and cancer cell growth, we should not invest in this kind of research," he added.
Currently, the three main approaches to managing prostate cancer are active
surveillance, radiation and surgery.
