Phytotherapy and Nutritional Supplements on Breast Cancer 用于乳腺癌治疗的植物疗法和营养补充剂

4.2.4. Selenium

Selenium is an antioxidant mineral that activates enzymes (e.g., glutathione peroxidase) which participate in the metabolism of oxidants and drugs [412]. However, this activation is dependent on the physiological selenium concentrations which should be between 70 and 90 mcg/L [413]. In humans, physiological selenium concentrations depend on the intake of food products containing high levels of selenium (e.g., grains, cereals, organ meats, and seafood, with lower amounts in dairy products, fruits, and vegetables), the selenium content in soil of each geographic region, and the supplementation [397]. However different organic nutritional forms of selenium are available for cancer prevention; sodium selenite is the favourite form of selenium for therapeutic purposes [414].

Selenium appears to be a crucial trace element recognized in some types of cancers as cancer-protective agent [415]. Adequate selenium levels should be maintained to provide therapeutic benefits such as preventive activity in breast cancer [416]. In a meta-analysis, prospective studies demonstrated the protective effect in cancer incidence when patients were supplemented with selenium in the case of deficiency in physiological levels [417]. Nevertheless, the results from studies are again unclear. In another meta-analysis study, the authors evaluated the association between selenium exposure/supplement and cancer risk and did not find a protective efficacy of selenium supplement [418]. Additionally, different effects (i.e., decreased or not associated effect) on specific types of cancer were reported; namely, it decreased the risk of breast cancer. In a review paper related to the prevention of cancer by selenium, the authors reported that positive evidence was only achieved from epidemiological data and not from randomized studies [415]. From this perspective, before the supplementation of cancer patients with selenium (e.g., sodium selenite), the individual selenium status should be measured (e.g., selenium in whole blood) [419] to avoid overdosing and side effects such as higher incidence of serum lipids, hypertension, and diabetes [391].

To investigate the input of selenium and other trace elements in the etiology of breast cancer, Adeoti and collaborators determined the serum concentration of these elements in breast cancer patients [420]. An inverse relationship between the concentration of zinc and selenium in the venous blood was verified while that of the control reported a direct relationship. The authors demonstrated the association between the serum concentration of trace elements, including selenium, and breast cancer.

In addition, selenium seems to reduce the side effects of radiotherapy and does not affect the efficacy of conventional treatments [421]. In this study, diarrhoea was significantly reduced in the group supplemented with selenium.