Women who took a nutritional supplement, a multivitamin or extra vitamin E had a smaller drop in neutrophils, white blood cells that help fight bacterial infections, according to a study published in Cancer.
To investigate whether supplements help reduce side effects from chemotherapy, Dr Richard Branda - who led the study, and his colleagues from the University of Vermont in Burlington - asked 49 women with breast cancer to complete questionnaires detailing their use of supplements during chemotherapy.
The authors found that more than 70 per cent of the women were taking at least one of 165 different types of supplements. On average, patients took three supplements. However, some women said they took up to 20 daily supplements during treatment.
The most common supplements were multivitamins, vitamin E and calcium. Women who took multivitamins or vitamin E alone experienced a smaller decrease in their neutrophils during chemotherapy.
However, women with relatively high levels of B-vitamin folate had a larger-than-average drop in neutrophils.
Branda also cautioned that chemotherapy patients should first discuss taking supplements with their doctors, because some supplements may interfere with treatment. For instance, cod liver oil and St. John's Wort may interfere with blood thinning drugs, hormone treatment or chemotherapy.
A study carried out in the UK in January suggested that more than half of cancer patients were taking herbal remedies and supplements alongside conventional treatment, which could be putting them at increased risk of dangerous side effects.
Researchers, led by Dr Ursula Werneke at Homerton Hospital's psychiatric unit in London, then issued warnings to 12 per cent of patients studied, cautioning that their use of garlic, cod liver oil and St John's wort could interfere with some standard cancer treatments.
More than 300 patients attending an outpatient clinic at a specialist cancer centre in London's Royal Marsden Hospital completed multiple-choice questionnaires for the study. They revealed that over 50 per cent of them took supplements - 42 per cent of these were taking only supplements, 10.4 per cent herbals only and the rest were taking a combination of both. Fewer than half those taking complementary medicine had discussed this with the doctor overseeing their conventional treatment
The report also found that around one third of those patients were unsure of the purpose of the remedy they were taking. And 11 per cent of patients reported taking supplements higher than the recommended doses.
The researchers however did note that they had not identified how the potential risks translate into actual events and research is needed to establish the frequency and seriousness of such side effects.
After the results of this latest study Branda noted that supplements typically consist of complex chemicals, which can have many possible effects on the metabolism of drugs and the functioning of cells.
"These effects may be beneficial or detrimental and need to be studied further," he said.
For instance, based on the results with folate, Branda recommended that cancer patients avoid taking extra folate if they eat a balanced diet, because many foods are already fortified with folate, or folic acid.