Antioxidants in breast cancer therapy

February 20 2019

A recent research paper has received much public awareness in Denmark.

It is about a German epidemiological cohort study of 2223 postmenopausal breast cancer patients enrolled in 2002-2005 and followed until July 2015.

The paper concluded:

  • That antioxidant use during chemotherapy or radiation therapy was associated with poorer breast cancer prognosis in postmenopausal women.
  • However, there was no overall association between postdiagnosis antioxidant use and breast cancer prognosis.

Only a few studies have previously examined the impact of various antioxidants on breast cancer prognosis, and the results have been different or inconclusive. These studies had been heterogeneous in terms of population size, participant age, types of supplements studied, and dose, timing, and duration of the antioxidant(s) used.

Can we really trust the new study? Certainly not!

I will explain why in the following !

The patients were grouped as:

  • Prediagnosis user was determined at the recruitment interview. 807 women (36%).
  • A postdiagnosis user was a woman who had any supplement use after breast cancer diagnosis. 989 women (45%).
  • A current user was a woman who used supplement postdiagnosis within the 6 mo before the first follow-up interview. 878 women (40%)
  • A consistent user was a woman who had used a supplement both pre- and postdiagnosis .
  • A concurrent user was a woman who had used antioxidants postdiagnosis for ≥1 mo. while simultaneously undergoing chemotherapy and/or radiation therapy. 167 women (9%).
  • A nonuser was a woman who had not used any supplement postdiagnosis.

Advanced statistical analysis methods, including the Delayed-Entry Cox Proportional Hazard Models, were used to estimate Hazard Ratios (HRs) and 95% Confidence Intervals (CIs). The significance level was set to 5%.

In total, 457 women in the study used antioxidants. The relative proportions of antioxidants used were: Selenium (40.5%), multivitamins (36.3%), zinc (30.4%), vitamin C (16.2%), vitamin E (16.2%), and vitamin A (3.1%).

In the study use of vitamin or mineral (antioxidant) supplements was defined as regular use (≥3 times/wk) of any vitamin or mineral supplements for ≥1 y.

In order to ensure adequate statistical power for survival analyses, use of different antioxidants was combined into 1 antioxidant variable. Thus the exposure parameter used in this study was very simple: Supplementation or no supplementation of antioxidants.

Based on that, the analysis of the relatively small concurrent antioxidant user group of 187 women showed a statistical significant poorer breast cancer prognosis, than the patients not taking antioxidant supplements..

However, in human epidemiological studies the exposure details are as important as the disease parameters. However, in this study the exposure assessment was as a black box.

It was not specified, which single antioxidant chemicals or mixtures of antioxidants the patient groups had taken, or the amount/doses of antioxidants administrated. Such information have crucial importance for the exposure assessment.

Neither, there was information on postdiagnosis dietary intake of antioxidants, which also might had changed the conclusion.

A quality study had determined the antioxidant levels in the patient’s blood, and used these results for their statistical analysis. The authors failed with that, making their study results completely arbitrary and therefore considered political or junk science. It seems that the authors accepted and were happy with the outcome of the study, because the outcome happened to be, what they expected and believed in beforehand.

The science of antioxidant vitamins and minerals is very complex. Antioxidants are very different in nature and effects, and there are various interactions between antioxidants, and mixtures of antioxidants have often more than additive effects.

The authors know that, because, in their paper, they mentioned two other studies where vitamin C and carotenoids, respectively, were the antioxidants studied, and these studies gave completely opposite results!

It is also remarkable that the conclusion in the abstract:

“Results from our study align with the current recommendation to possibly avoid the use of antioxidants during chemotherapy or radiation therapy”,

is more political and alarming than the more balanced conclusion at the end of the paper:

“Our results, together with other clinical and experimental evidence, suggest that during breast cancer treatment antioxidants should potentially be used with caution.”

Based upon the new study the Danish Cancer Society has recommended Danish breast cancer patients to avoid antioxidants supplementations during cancer treatments.

That is not a reasonable action based on an insufficient research study!

Will that mean that the Cancer Society also recommend cancer patients to avoid intake of antioxidants with the food during treatment? It is well-known that there may be no differences between antioxidants in food and the same antioxidants in supplements. Further, do the Society believe that it would be better for the patients’ survival to eat unhealthy food without vitamins and minerals during treatments?

Probably not! It has been known for more than 30 years that radiation and chemical therapy kills both cancer cells and healthy cells mainly by oxidation, and that the rapid growing cancer cells will be more susceptible to the treatment than the healthy cells.

In order for the patients to recover and survive it is necessary, that the healthy cells are protected sufficient against oxidations caused by the treatments. A patient in good shape will tolerate the treatment better, be more resistant to side-effects and should have a better prognosis.

The US National Cancer Institute has published a more balanced evaluation of a complex topic.

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