(RxWiki News) Half of all Americans take at least one dietary supplement with the belief that it enhances health and may prevent disease. Yet when it comes to cancer prevention, high-dose supplements may cause more harm than good, according to a recent analysis.
While animal, lab and observational studies have hinted that certain supplements can reduce the risk of cancer, the few randomized clinical trials have not proved these claims. And some gold-standard research studies have shown that supplements can actually increase the risk of cancer.
"Tell your doctor about all medicines you're taking, including supplements."
To find out about what impact dietary supplements have on cancer risk, Maria Elena Martinez, PhD, of the University of California San Diego Moores Cancer Center and colleagues reviewed observational studies. They examined studies of anti-oxidants, folic acid, vitamin D and calcium.
In terms of anti-oxidants, the authors write there is no firm link between supplements and reducing the development of cancer. In fact, they assert that anti-oxidant supplements "may well be a two-edged sword" and interfere with protective processes.
Several studied reviewed found that supplements actually increased the risk of certain cancers.
- The Beta-Carotene and Retinol Efficacy Trial (CARET) involving beta-carotene given to high-risk groups found a 33 percent increase in lung cancer, compared to those given a placebo.
- The Alpha-Tocopherol, Beta-Carotene (ATBC) Trial found similar results.
- A study involving selenium showed an increased risk of squamous cell skin cancer.
- The Selenium and Vitamin E Cancer Prevention Trial (SELECT) found an increase in prostate cancer among men taking vitamin E supplements.
Before more randomized control trials can be conducted over a number of years rather than just a few, researchers caution against the use of dietary supplements for cancer prevention.
Yet, the scientists say they know people will continue to take supplements believing that at worst they are harmless and at best may be beneficial.
"These beliefs underscore the need for efforts by scientists and government officials to encourage the public to make prudent decisions based on sound evidence with respect to use of dietary supplements for cancer prevention," the authors write.
This work was published April 25 in the Journal of the National Cancer Institute.
The study was funded by the National Cancer Institute. No conflict of interest disclosures were reported.