Dietary supplements and cancer: promises and realities
A dietary supplement can be defined as any vitamin, mineral, protein, enzyme, probiotic, herb, or plant substance taken to supplement dietary needs or improve body functions. Although some dietary supplements may be injected, the vast majority come in the form of pills, powders and liquids that are ingested.
Dietary supplements are very widely used among patients with cancer and cancer survivors. Many perceive them to have potential anticancer activity, while many others use them to try to reduce the side effects of cancer treatment or to prevent the recurrence of new tumors. Although in some cases the use of these supplements is prescribed by doctors (when a cancer patient’s blood test results indicate a vitamin deficiency, for example), on many occasions cancer patients and survivors decide to use dietary supplements on their own, without any formal recommendation by their oncologists or primary care physicians.
It is relatively common for the dietary supplements in question to have shown antitumor activity in preclinical studies or small exploratory, nonrandomized, early-phase clinical trials. From these promising results, many supplements have been promoted for their purported ability to prevent (or even treat) cancer or ameliorate cancer treatment-derived side effects. Although the use of this kind of supplements among cancer patients and survivors is extremely common, robust information on their actual clinical efficacy is in many cases still very limited.
Oncologists are often challenged in providing advice to patients about which supplements are safe and effective to use to treat or prevent cancer or cancer therapy side effects, especially since favorable preclinical results usually do not translate to success in clinical trials. Additionally, in a clinical setting with treated patients, some supplements might even be antagonistic to standard treatment with chemotherapy, radiation, targeted therapy and/or immunotherapy. The lack of robust clinical results involving dietary supplements and cancer patients or survivors greatly complicates the job of medical professionals in advising about the efficacy and safety of their use.
The generation of solid clinical evidence on dietary supplements in cancer can therefore be considered an urgent, unmet need, although there are many challenges associated to the generation of such evidence. Impossibility for patent protection entails a lack of financial incentives to fund large clinical trials, and manufacturing difficulties might generate limited product consistencies, disputing the extrapolation of the results. Despite all these difficulties, the design and development of strategic, scientifically sound clinical trials able to shed some light into the convenience of using dietary supplements for cancer-related purposes is a necessity that all health-related stakeholders should address. Patients, physicians and health systems worldwide could greatly benefit from the potential results.
Roldan Cortés, MedSIR.