Chemotherapy and radiation continue to be the major forms of treatment for many types of cancer. The considerable toxicity of these treatments to normal cells is a problem in cancer treatment and management.
Selenium’s Role in Cancer Prevention
Selenium supplementation has already been associated with statistically significant reductions in the risk of various cancers and pre-cancerous conditions:
- Linxian Nutrition Intervention Trials [Blot 1993]
- Nutritional Prevention of Cancer Trial [Clark 1996, 1998]
- Su.Vi.Max. Trial [Hercberg 2004]
- Long-term Reduction of Recurrent Adenomas [Bonelli 2013]
Possible Role for Selenium in Cancer Treatment
Selenium supplementation may be valuable in the treatment of cancer as well as in the prevention of cancer. Selenium has the ability to protect against the formation and progression of some cancer cells and also the ability to selectively target some existing cancer cells.
Moreover, it may be that selenium can work in synergy with conventional cancer therapies. Pre-clinical research data suggest that selenium may in some instances protect normal cells and tissues against the toxic effects of conventional cancer treatments on the cells [Evans 2017].
Pre-clinical Research into Selenium and Cancer Therapies
There is considerable pre-clinical research suggesting that selenium supplements may significantly protect against the normal tissue toxicities of conventional cancer therapies without compromising those same cancer therapies’ anti-cancer effects. In some cases, selenium supplements in the right formulation and the right dosage may even enhance the effectiveness of the conventional cancer therapies [Evans 2017].
Which Selenium Formulations and Dosages for Anti-Cancer Effects?
In pre-clinical models, administration of selenium has enabled the administration of higher than normal doses of the cyto-toxic anti-cancer agents. The result of using selenium to modulate the conventional cancer treatment in pre-clinical studies may be improved cancer outcomes [Evans 2017].
What is needed now is clinical trials of selenium supplementation to see which selenium supplement formulations and which selenium dosages are safe and effective in cancer treatment. The available evidence indicates that organic selenium is safer and likely more efficacious than inorganic selenium is [Evans 2017].
Pre-clinical studies have shown, however, that inorganic sodium selenite administered at high dosages does have anti-tumor effects and does increase the efficacy of drugs that inhibit cell growth. Swedish researchers found that IV sodium selenite in high doses was safe and tolerable in patients with therapy-resistant carcinomas. In future articles, I will try to review the results of studies using both inorganic and organic selenium for cancer treatment [Brodin 2015].
Supra-Nutritional Dosages of Selenium and Cancer Therapies
Evans et al have summarized the evidence for a therapeutic synergy of supra-nutritional doses of selenium compounds with the following chemotherapy drugs [Evans 2017]:
- Cisplatin
- Carboplatin
- Oxaliplatin
- Irinotecan
- Docetaxel
- Fluorouracil
- Doxorubicin
The enhancement of the above chemotherapy drugs through combination with selenium has been demonstrated in the following human tumor tissue grafts [Evans 2017]:
- Colo-rectal tissue
- Ovarian tissue
- Prostate tissue
- Small cell and non-small cell lung carcinoma
- Head and neck squamous cell carcinoma
- Leukemia cells
What are Supra-Nutritional Dosages of Selenium?
Supra-nutritional dosages of selenium are understood to be dosages above the normal daily intakes of selenium, which are estimated to be 134 micrograms (adult men) and 93 micrograms (adult women) from food in the United States [Office 2019]. Daily intakes of selenium in most regions in Europe and the Middle East are considerably lower than the average daily intakes in the United States [Stoffaneller & Morse 2015].
Accordingly, a supra-nutritional dosage of selenium could be any supplemental dosage in the range from 200 micrograms/day to 800 micrograms/day.
Note: Supra-nutritional dosages (200 micrograms/day) administered to selenium-replete individuals did not result in significant protection against prostate cancer risk in The Selenium and Vitamin E Cancer Prevention Trial (SELECT) in which the participating men had an average baseline serum selenium concentration of 135 micrograms per liter [Lippman 2009].
By contrast, participants in the Nutritional Prevention of Cancer Trial who had an average baseline plasma selenium concentration below 123.2 micrograms per liter had significant reductions in prostate cancer risk associated with the daily intake of a 200-microgram selenium-enriched yeast supplement [Duffield-Lillico 2003].
Conclusion: Selenium Supplementation and Cancer
Clinical studies have shown that selenium might play a role in the prevention of some cancers. Selenium’s cancer-preventive effect is thought to be related to its effects on DNA repair, on apoptosis, on antioxidant activity, and on the functioning of the endocrine and immune systems [Office 2019].
Evans et al have presented the pre-clinical research evidence suggesting that selenium compounds may significantly protect against the normal tissue toxicities of cancer therapies without compromising the cancer therapies’ anti-cancer efficacy (and possibly even enhancing the anti-cancer efficacy [Evans 2017].
Sources
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Bonelli, L., Puntoni, M., Gatteschi, B., Massa, P., Missale, G., Munizzi, F., & Bruzzi, P. (2013). Antioxidant supplement and long-term reduction of recurrent adenomas of the large bowel. A double-blind randomized trial. Journal of Gastroenterology, 48(6), 698-705.
Brodin, O., Eksborg, S., Wallenberg, M., Asker-Hagelberg, C., Larsen, E. H., Mohlkert, D., … Björnstedt, M. (2015). Pharmacokinetics and Toxicity of Sodium Selenite in the Treatment of Patients
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Duffield-Lillico AJ, Dalkin BL, Reid ME, Turnbull BW, Slate EH, Jacobs ET, et al. (2003). Selenium supplementation, baseline plasma selenium status and incidence of prostate cancer: an analysis of the complete treatment period of the Nutritional Prevention of Cancer Trial. BJU Int; 91:608-12.
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The information presented in this review article is not intended as medical advice and should not be used as such.
2 November 2019