# Confirm or refute the harm of antioxidant supplements during chemotherapy

Source: https://onco.cc/ideas/idea-nl-antioxidant-supplement-harm-confirmation/  
OnCo record `idea-nl-antioxidant-supplement-harm-confirmation` (Idea). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Half of patients take antioxidant vitamins during chemotherapy. One good observational study suggests they raise recurrence by 40%. Patients deserve a definitive answer, and it can be obtained cheaply by adding supplement tracking to trials already running.

## Summary

The DELCaP study nested in a breast cancer chemotherapy trial found that antioxidant supplements (vitamins A, C, E, carotenoids, coenzyme Q10) taken before and during chemotherapy were associated with a 41% higher recurrence and 40% higher mortality, with similar signals for vitamin B12, iron and omega-3. Randomised harm has been shown for beta-carotene in smokers and for antioxidants during head and neck radiotherapy. A randomised trial of antioxidants during chemotherapy is now ethically difficult; the pragmatic path is prospective supplement capture in every adjuvant trial and a pre-registered pooled analysis, plus a randomised trial of a stop-supplement counselling intervention.

## Fields

- Kind: Idea
- Last checked: 2026-09-08
- Hypothesis: Prospectively recorded antioxidant supplement use during adjuvant chemotherapy is associated with worse disease-free survival across tumour types after adjustment, and a pharmacist-led counselling intervention at chemotherapy start reduces antioxidant use by half and is acceptable to patients.
- Rationale: The mechanism (scavenging of the reactive oxygen species that mediate cytotoxic and radiation cell kill) is coherent, the observational signal is large, and the exposure is common, modifiable and almost never recorded. Patients currently receive contradictory advice from oncologists, pharmacies and the internet.
- Proposed test: Add a standardised supplement questionnaire to three ongoing adjuvant chemotherapy trials (breast, colorectal, lung) with a pre-registered pooled analysis; in parallel, a cluster-randomised trial of pharmacist supplement reconciliation and counselling at chemotherapy initiation with supplement cessation and patient satisfaction as endpoints.
- Maturity: early-clinical
- Actor: research

## Sources

- Bottleneck evidence (Misinformation and unproven therapies): Johnson et al., Cancer misinformation and harmful information on Facebook and other social media (JNCI 2022): https://doi.org/10.1093/jnci/djab141

## Connected records

- ideas: [An open supplement-drug interaction checker built into oncology prescribing](https://onco.cc/ideas/idea-moon-supplement-interaction-database/)
- cancers: [Colorectal cancer](https://onco.cc/cancers/colorectal/), [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/), [Non-small-cell lung cancer](https://onco.cc/cancers/nsclc/), [Triple-negative breast cancer (TNBC)](https://onco.cc/cancers/tnbc/)
- fronts: [Diet, Exercise & Lifestyle](https://onco.cc/fronts/nutrition-lifestyle/), [Supportive Care & Survivorship](https://onco.cc/fronts/supportive-care/)
- technologies: [Cytotoxic chemotherapy](https://onco.cc/technologies/cytotoxic-chemotherapy/), [Dietary supplements during cancer treatment: interactions and harms](https://onco.cc/technologies/dietary-supplements-treatment-interactions/), [Oncology nutrition assessment and medical nutrition therapy](https://onco.cc/technologies/nutrition-screening-mnt/)
- drugs: [Doxorubicin](https://onco.cc/drugs/doxorubicin/), [Paclitaxel / nab-paclitaxel](https://onco.cc/drugs/paclitaxel/)
- institutions: [Memorial Sloan Kettering Cancer Center](https://onco.cc/institutions/mskcc/)
- terms: [Unproven diet claims (alkaline, juice, 'anti-cancer' diets)](https://onco.cc/terms/unproven-diet-claims/)
- bottlenecks: [Misinformation and unproven therapies](https://onco.cc/bottlenecks/b-misinformation/), [Toxicity and quality of life are undervalued](https://onco.cc/bottlenecks/b-toxicity-qol/), [Weak real-world evidence and registries](https://onco.cc/bottlenecks/b-real-world-evidence/)
- key papers: [Cancer Misinformation and Harmful Information on Facebook and Other Social Media: A Brief Report](https://onco.cc/key-papers/paper-johnson-j-natl-cancer-inst/)

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