• In a new study, researchers surveyed more than 1,000 people who had been diagnosed with breast, prostate, or colorectal cancer to ask about the use of dietary supplements.
• Around 20 percent of respondents said they believed dietary supplements could reduce the risk of cancer recurring (coming back), though no current research supports that belief.
• Researchers cautioned that supplements can interfere with certain cancer treatments and urged health care professionals to provide better guidance about supplements to people living with cancer.

In a recent study, 1 in 5 people diagnosed with cancer said dietary supplements could prevent the disease from recurring — though there’s no scientific evidence to support that belief. In fact, the authors of the study warned that some supplements can do more harm than good.

“There is no evidence that self-prescribed supplements reduce the risks of cancer coming back, and they could interfere with treatment,” said Dr. Rana Conway, the lead author of the study, in an interview with U.S. News & World Report.

For the study, researchers in the United Kingdom collected data from more than 1,000 people through mailed surveys, telephone interviews, and online surveys. Everyone in the study was an adult who had previously been diagnosed with breast, prostate, or colorectal cancer.

The study authors found that 19 percent of respondents said they thought dietary supplements could help prevent cancer from returning. Additionally, 40 percent people reported taking a supplement within the past 24 hours.

The results show that many cancer survivors believe that supplements can help with cancer prevention, researchers conclude. Notably, some dietary or herbal supplements may help people with cancer manage their symptoms or improve their sense of well-being. However, currently, there’s no research that shows that vitamins or supplements can help keep lung cancer or other types of cancer away.

Furthermore, some supplements may actually cause harm to people living with cancer. For example, some vitamins can make medications like chemotherapy less effective.

Conway noted that many people with cancer may be focusing on the wrong approaches to prevent cancer recurrence. “Most of us find healthy eating and exercise advice more difficult to stick to, but the evidence shows it offers real benefits,” she told U.S. News & World Report.

In order to reduce the risk that cancer will recur, organizations like the American Cancer Society recommend:

• Eating a variety of nutrient-rich foods
• Limiting consumption of red or processed meat
• Cutting back on sugar and refined grains
• Getting regular exercise, including both aerobic activity and strength-building workouts

People living with lung cancer should tell their health care team about any vitamins, herbs, or supplements that they are taking.