Cancer patients taking dietary supplements during treatment could be at risk of worse outcomes, experts have warned.
Britons spent £500 million a year on vitamins and supplements in 2020, according to market research.
A new study, carried out by Mayo Clinic in Rochester, Minnesota, found the majority – 91 per cent – of cancer patients take some form of supplement. Vitamin D, probiotics and multivitamins are the most popular.
Experts collected data from 100 cancer patients and cross-referenced the supplements with the latest data on natural medicine, to determine if they could be putting the patients at risk.
The experts recommended some 35 per cent of patients who were taking some form of supplement should stop.
They warned taking such pills, or other natural therapies including extreme diets or IV drips, raised the risk of toxicity – having excess vitamins in the body.
Supplements also increased the risk of interacting with and decreasing the effectiveness of the cancer treatment.
Supplements ‘can be dangerous in several ways’
All patients in the study were on active cancer treatment at the time, such as chemotherapy or radiotherapy.
Previous research, published in the Journal of Clinical Oncology, suggested patients who take antioxidant supplements before and during chemotherapy may have worse outcomes.
Some 1,134 people took part in the study and filled in questionnaires about their supplement use.
Researchers compared supplement use to relapse rates and death. They found people who took antioxidants before and after chemotherapy were 41 per cent more likely to have recurrence of breast cancer and 40 per cent more likely to die.
Dr Stacy D’Andre, an oncologist and lead author of this latest research, said: “I was surprised at how many patients take supplements and have used alternative therapies.
“These can be dangerous in several ways – they can be directly toxic, can interact with other medications and lead to increased side effects, they may decrease the effectiveness of cancer treatments, they are expensive and supplements are not regulated.
“It is essential that care teams know what patients take to ensure safety. We need to do a better job of educating the public that supplements or ‘natural’ therapies are not always safe.”
She added the results are likely to be replicated in the UK. “Literature from other countries shows that many cancer patients are taking supplements,” she added.
Dr D’Andre said patients may take supplements because they want to have more control over their situation and treatment. They may also take them after hearing stories of other patients doing well on alternative medicine, or because they have a preference for “natural” therapies instead of pharmaceuticals.
Check with your doctor first
Cancer Research UK has warned patients to check with a doctor before taking any supplements, to ensure they will not interfere with their treatment.
Martin Ledwick, head information nurse at Cancer Research UK, said: “We would always recommend that patients check with their doctor first before taking any supplements or complementary therapies.
“Some may have known interactions with cancer medicines which might make them less effective or even increase side effects.
“But, in many cases, interactions with conventional treatments might not be known, so it is always sensible to be cautious about taking anything that has not been prescribed by your doctor when undergoing cancer treatment.”
The findings were presented at the American Society of Clinical Oncology conference in Chicago.