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October 15, 2020 | 5 minute read

Study Suggests Supplements During Breast Cancer Chemotherapy May be Harmful

After a cancer diagnosis, many people look to dietary supplements for a health boost. However, a recent study adds to the concern about using supplements during treatment, finding that breast cancer patients who take certain supplements both before and during chemotherapy may be at increased risk of recurrence and an earlier death.

The study was published in the Journal of Clinical Oncology.

It adds to a small but growing body of research on supplement use and cancer treatment. A previous study focusing on colorectal cancer found that taking a multivitamin during chemotherapy did not improve or worsen recurrence or survival. Other research in this area has shown mixed findings and have raised the possibilities of harm.

Overall, research on supplement use and cancer risk and treatment has led AICR, and other major health organizations, to advise caution on their use.

“We do not recommend supplements for cancer prevention or in the treatment setting, so this study supports that approach,” says Nigel Brockton, PhD, AICR’s Vice President of Research. “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.”

“There has been a lot of debate about supplements,” says Christine B. Ambrosone, PhD, chair of the Department of Cancer Prevention and Control at Roswell Park Comprehensive Cancer Center and lead author of the study. Some said don’t take during treatment; some thought the other way. “But it’s not based on any solid data.”

There is research that suggests antioxidant supplements in particular actually block the effectiveness of chemotherapy and radiation. These treatments may destroy cancer cells by producing reactive oxygen species, also known as free radicals, and antioxidants break down these free radicals.

Dietary supplements and cancer survival

The 1,134 patients in this study had all been diagnosed with high-risk breast cancer that was more likely to recur and they were already enrolled in a chemotherapy trial. The patients completed two questionnaires on their use of dietary supplements; once when they were first assigned to a treatment group and then again six months after their chemotherapy.

After following the patients for 15 years, or until death, the strongest links to recurrence and death were found with vitamin B12, iron and omega-3 fatty acids. Taking vitamin B12 both before and during chemotherapy, for example, linked to an 83 percent decrease in disease-free survival compared to patients who did not take the supplement. This was after accounting for other risk factors, such as patients’ age, tumor characteristics, smoking and alcohol consumption.

Findings pointed towards – but were not as clear – a higher risk of recurrence and death with using any antioxidant dietary supplements, including vitamins A, C and E along with carotenoids and coenzyme Q10. Multivitamin use was not linked with either recurrence or survival.

The inconclusive findings for antioxidants could relate to the relatively small numbers of patients and supplement users. “We didn’t have the statistical power we would have liked,” said Ambrosone.

Reports estimate that about 40 to 60 percent of cancer patients may take supplements. In this study, however, antioxidant supplements use was relatively low, and it decreased during treatment. Among the study participants, 18 percent took an antioxidant during treatment and 44 percent took multivitamins. Vitamin C, for example, was used by 20 percent of patients before treatment and only 12 percent during chemotherapy. The relatively low use could be due to this specific group and/or that many of these patients spoke with their doctors about supplement use and were advised against taking them during treatment.

This study is observational; it does not show a cause and effect. The group of high-risk breast cancer patients also may not be generalizable to the broader breast cancer population. But it provides additional support to the existing evidence that use of certain dietary supplements during chemotherapy may increase the risk of worse outcomes, the study concludes. “It is certainly reason to be cautious,” notes Brockton.

Cancer patients and supplements

More than half of US adults take dietary supplements and there are reasons patients undergoing cancer treatment — and others — may need to take them. Talk about supplement use with your doctor, experts advise.

“There may be individualized situations when a person needs repletion or supplementation, but that would be handled by the healthcare team,” said Angela Hummel, MS, RD, CSO, a consulting dietitian with AICR and specialist in oncology nutrition. “If side effects from treatment cause a reduced ability to eat and maintain lean body mass, it is important to work with a registered dietitian on techniques and strategies to help.”

“As an oncology nutrition practitioner, it is wonderful to see published research in this area because people with cancer are wanting to know what is the best course of action in regards to taking supplements while undergoing treatment,” said Hummel. “I hope that this is just a glimpse of what is to come.”

Ambrosone and her colleagues are currently conducting a larger study of supplement use among breast cancer patients. Her guidance mirrors that of AICR experts, suggesting cancer patients try to get their needed vitamin and mineral from eating a variety of foods, including vegetables, fruits and whole grains. “When you just pluck out specific vitamins and minerals from foods, you are losing all the effects that are probably there when using these nutrients from food,” she said.

The study was supported by grants that include the Breast Cancer Research Foundation and Roswell Park Comprehensive Cancer Center Support Grant National Cancer Institute, Division of Cancer Prevention.

For lower cancer risk in general, AICR recommends people aim to meet their nutritional needs through diet and not rely on supplements. Cancer patients and survivors can find guidance on healthy actions to take before, during and after cancer treatment by reading AICR’s Treatment Tips.

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