Though dietary supplements can offer health benefits, Dr. Byers says "there is no substitute for good, nutritional food."
The use of dietary supplements is common in the US, with more than half of Americans reporting regular use of at least one form, according to a National Health and Nutrition Examination Survey (NHANES).
The purpose of dietary supplements is to help the body achieve essential nutrients that it may not be getting from food, though numerous studies have suggested they pose additional health benefits.
Last month, for example, Medical News Today reported on a study suggesting vitamin D supplements may slow or reverse the progression of low-grade prostate tumors.
But in recent years, a number of studies have suggested that dietary supplements may raise the risk of cancer rather than reduce it. Dr. Tim Byers, of the University of Colorado Cancer Center, is one researcher who has been involved in such studies.
Dietary supplements 'no substitute for good, nutritional food'
According to Dr. Byers, initial tests of dietary supplements in animal models indicated they protect against cancer development.
But on testing these dietary supplements in humans, Dr. Byers and colleagues found they may have the opposite effect for some individuals.
"We studied thousands of patients for 10 years who were taking dietary supplements and placebos," he says. "We found that the supplements were actually not beneficial for their health. In fact, some people actually got more cancer while on the vitamins."
Dr. Byers points to one study that investigated the effects of beta carotene supplements in humans. The results of the study revealed that individuals who took beta carotene at doses higher than the recommended levels were at 20% increased risk of both lung cancer and heart disease.
What is more, Dr. Byers speaks of another study that associated use of folic acid supplements with an increased number of polyps in patients with colon cancer, despite this particular supplement being previously associated with a reduction in the number of polyps.
Dr. Byers notes that these findings should not deter people from taking vitamins and minerals; at the correct dosage, they can pose health benefits. It is when people take too many that the problems occur. He adds:
"At the end of the day we have discovered that taking extra vitamins and minerals do more harm than good."
In addition, he stresses "there is no substitute for good, nutritional food," noting that the majority of people can get all the vitamins and minerals they need through a healthy diet.
Earlier this month, Medical News Today reported on a study published in Drug Testing and Analysis, which revealed that many dietary supplements still contain an amphetamine-like stimulant 2 years after the Food and Drug Administration (FDA) first flagged the issue.