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Experts say vitamins and other supplements can lessen the effectiveness of chemotherapy and radiation treatments. ALTO IMAGES/Stocksy
  • Researchers say vitamins and other supplements taken during breast cancer treatment can cause a higher risk of recurrence.
  • Experts note that chemotherapy and radiation are designed to cause damage to cancer cells, while supplements’ main job is to repair cell damage.
  • They recommend that people undergoing breast cancer treatment get their nutrients through a healthy, well-balanced diet.

When you’re in treatment for breast cancer, nutrition can be a challenge.

In an effort to get essential nutrients, you may think it’s a good time to add dietary supplements to your regimen.

But some supplements, particularly antioxidants, may interfere with cancer treatment.

A recent study suggests that people with breast cancer taking certain supplements before and during chemotherapy may be at increased risk for recurrence of the disease and earlier death.

The study is published in the Journal of Clinical Oncology.

The American Institute for Cancer Research (AICR) is advising people with cancer to use caution with dietary supplements.

“We do not recommend supplements for cancer prevention or in the treatment setting, so this study supports that approach,” Nigel Brockton, PhD, the AICR vice president of research, said in a column on the organization’s website.

“Not only is there no benefit, but they may be harmful. Our best recommendations remain to obtain nutritional requirements from a plant-based, whole foods diet,” he added.

The American Cancer Society and National Cancer Institute make similar recommendations.

The observational study involved more than 1,100 high-risk, early stage breast cancer patients who were followed for a median of 6 years.

The researchers said they found:

  • Patients who took antioxidants, including vitamins A, C, and E as well as carotenoids and coenzyme Q10, both before and during chemotherapy were more likely to have a recurrence.
  • Those who took vitamin B12, iron, and omega-3 fatty acid supplements were at significantly greater risk for recurrence and death.
  • Multivitamins didn’t appear to affect outcomes after chemotherapy.

Although results aren’t definitive, the study authors conclude that results are consistent with recommendations of caution among people with cancer.

Dr. Jack Jacoub is a medical oncologist and medical director of MemorialCare Cancer Institute at Orange Coast Medical Center in Fountain Valley, California.

Jacoub told Healthline that there aren’t enough high-quality studies to make firm conclusions.

“Nonetheless, we have enough information to be able to make a recommendation. This general opinion is accepted and we share that with patients,” he said.

“And not just those with breast cancer. It applies to all patients in cancer treatment, specifically chemotherapy and radiation,” Jacoub added.

“The core of the problem is this conglomeration of cells creating a tumor,” Jacoub said.

He explained that chemotherapy and radiation treatments are intended to cause cellular damage and cellular death.

“If this is the goal, why would you do something that can theoretically counteract that? Antioxidants are reparative. They function to heal cells,” Jacoub said.

“One of the things we’re dealing with are alternative clinics that suggest high-dose supplements to combat cancer therapy. There’s not enough high-quality data to say that’s safe. You should try to keep your system pure. Finish treatment first,” he continued.

“From the perspective of patients, supplements may be helping with side effects or nutrition. That’s understandable. But they can do other things to get to that same point without supplements,” Jacoub said.

“There’s an abundance of statistics suggesting that people don’t tell their doctor everything they’re taking. That’s where risk comes in. Outcomes could be affected if you don’t really share everything you’re taking,” he added.

Jacoub advises waiting 4 to 6 weeks after treatment to resume your typical supplements, noting that it’s a case-by-case situation.

Dr. Crystal Fancher is a surgical breast oncologist at the Margie Petersen Breast Center at Providence Saint John’s Health Center in Santa Monica, California.

Fancher told Healthline that her practice recommends that patients obtain essential nutrients through diet.

“For the most part, we don’t advise supplements unless indicated by a medical condition,” she said.

She’s less concerned about multivitamins.

“Data shows there aren’t issues with multivitamins because they’re not high dose. Other studies on multivitamins show no benefits or negatives to taking them,” Fancher said.

Fancher points out that most people being treated for cancer have multiple doctors.

“We all have a different aspect of care, so it’s important that all your physicians know exactly what you’re taking,” she said.

Fancher recommends a healthy, balanced diet that includes lots of fresh fruit, vegetables, and whole grains.

She also emphasizes the importance of physical activity.

“We know that maintaining a healthy weight, having a balanced diet, and a good amount of activity are way more important than taking dietary supplements,” she said.

Fancher notes that treatment is individualized, and some people may have a condition that requires a supplement.

“If you’re under the care of a physician, taking some supplementation is not necessarily bad. If you have a special condition that requires it, that’s fine. But don’t take a supplement just because you think more is better,” she said.

“Many people don’t understand how to up their intake if they’re lacking a certain nutrient. A lot of breast centers around the country are trying to integrate nutrition with patient care. We have dietitians here who are very invested in cancer care and talking to patients to help them understand how to get necessary nutrients in their diet,” Fancher said.

“We advise our patients to make a list of everything they’re taking and review them with each treating physician,” she said.