FRIDAY, Aug. 27 (HealthDay News) -- Nutritional supplements are popular among Americans but people need to educate themselves and use caution when using these products to try to reduce their risk of cancer, says a University of Texas expert.

"Researchers are still unsure about whether or not minerals, herbs and other plants taken in pill, capsule, tablet or liquid form actually prevent cancer," Sally Scroggs, health education manager at the Cancer Prevention Center at the University of Texas M.D. Anderson Medical Center, said in a news release from the center.

Vitamins E and C, for example, were found not to prevent cancer in the large-scale Women's Health Study and the Physicians' Health Study II. Findings from other studies suggest that some supplements may actually increase cancer risk by affecting the balance of nutrients in the body.

"If you eat lots of vegetables, fruits, whole grains and beans, you should get the nutrients, including fiber, vitamins and minerals, your body needs to lower your chances of getting diseases like cancer," Scroggs said. "Taking a pill can't replace a healthy diet."

She suggested eating plenty of foods loaded with cancer-fighting nutrients such as beta-carotene, selenium, lycopene, resveratrol and vitamins A, C and E.

While Scroggs does advise caution, there are some situations where taking supplements may benefit people, especially those who aren't getting enough nutrients due to food allergies, genetics or chronic illnesses, she said.

This includes women who are pregnant or breast-feeding; people at risk for vitamin D deficiency or osteoporosis; and people at risk for B-12 deficiency, including those aged 50 and older and vegans who consume no animal products.

Scroggs concluded that if you're considering taking supplements, consult with a doctor or registered dietician first.

More information

The U.S. Food and Drug Administration has more about dietary supplements.