February 12, 2019
One could justifiably use the above-mentioned Shakespeare title about a newly published article (1) that supposedly shows that antioxidant supplements reduce the effectiveness of chemotherapy and radiation therapy in postmenopausal women.
Please note that this assertion is by no means proven; there is much research that points in both directions.
The above-mentioned journal article does not contribute to clarification of the issue, not least because of the weak design of the study.
The data in the study came from interviews of postmenopausal women in two regions in Germany. The researchers used data from the “Mamma Carcinoma Risk Factor Investigation,” a study that was first published more than 10 years ago to report on the risk factors associated with postmenopausal hormone therapy.
Despite the known weaknesses of the interview study, the Danish TV2 reported the results of the study as a great sensation and with a headline that announced:
“New research: Dietary supplements can spread breast cancer.
German researchers have learned that antioxidant supplements can worsen breast cancer in women. The Danish Cancer Society is concerned.
For many years, there have been discussions as to whether antioxidant supplements are good for human health or not. And now a German study makes it clear that they are definitely dangerous for women with breast cancer.”
No, no, and no again.
There is no evidence for the dramatic TV2 news statements.
The German study does not make anything clear.
And the journal article authors’ own conclusion is much more cautious than the TV2 news report.
The journal article authors write:
“Our data do not support an overall association of postdiagnosis supplement use with prognosis in postmenopausal breast cancer survivors. Our results, together with other clinical and experimental evidence, suggest that during breast cancer treatment, antioxidants should potentiall be used with caution.”
In their journal article, the authors do not even advise against the use of antioxidants during chemotherapy and radiation therapy. They just urge caution.
Normally, German research results are shrugged off in Denmark, and interview-format studies get the same treatment. But, this time, the German interview study could be used to advance specific points of view, and so it was.
There are many things in this German study that grab the attention of the alert reader, and a close reading of the study reveals that the authors are biased, not least in their selection of earlier research on the topic.
An interview study, with no blinding of at all, is certainly not the most valid form of research and cannot be compared with prospective randomized controlled trials (RCT’s).
In the German study, the researchers asked some 2000 breast cancer patients whether they took antioxidant supplements before and/or after the time of their diagnosis with breast cancer and/or during their chemotherapy and radiation therapy.
The women in the study were to answer yes if they had just taken one or another supplement three days a week for a year at a given point in time. A “current user” was any woman who used supplement postdiagnosis within the 6 months before the first follow-up interview.
The term “supplement” and the term “antioxidant” are used quite sloppily but with a noticeable consistency. Whenever the researchers discuss the study, the usage, or the statistics, they use the term “supplements.” Whenever they discuss the chemotherapy or the radiation therapy, however, they use the term “antioxidants” without specifying what the term “antioxidants” covers.
In other words, the researchers have had to extend the definition of antioxidants with other supplements in order to achieve sufficient statistical power and thereby just barely sneak over the line into statistical significance.
About this, the authors write in their article:
“The main exposures of interest included postdiagnosis use (no postdiagnosis use, postdiagnosis use, current use) of any type of supplement; specific supplements, such as magnesium and calcium; and supplement group, such as antioxidants, in which there was adequate statistical power to conduct analyses. Only a few women reported postdiagnosis use of multivitamins, vitamins A, C, E, zinc, and selenium, and therefore they were collectively evaluated together as antioxidants in all of our analyses.”
Above and beyond the fact that the researchers have jumbled everything together in a big group that they call “antioxidants,” there is also a total lack of information about daily dosages, single dosages, and preparation types.
This study has a weak design and has unclear results. Therefore, the authors are careful to settle for a cautious conclusion, which speaks for itself.
The misinformation occurs when the Danish media then trumpet the study conclusion as the definitive truth.
Any serious researcher would avoid making such bombastic statements.
- Jung AY et al. Antioxidant supplementation and breast cancer prognosis in postmenopausal women undergoing chemotherapy and radiation therapy. Am J Clin Nutr 2019;109:69–78.
- Flesch-Janys D, Slanger T, Mutschelknauss E, Kropp S, Obi N, Vettorazzi E, Braendle W, Bastert G, Hentschel S, Berger J. Risk of different histological types of postmenopausal breast cancer by type and regimen of menopausal hormone therapy. Int J Cancer 2008;123(4):933–41.