The Benefits and Hazards of Antioxidants: Controlling Apoptosis and Other Protective Mechanisms in Cancer Patients and the Human Population

Abstract

Cellular oxidants, called reactive oxygen species (ROS), are constantly produced in animal and human cells. Excessive ROS can induce oxidative damage in cell constituents and promote a number of degenerative diseases and aging. Cellular antioxidants protect against the damaging effects of ROS. However, in moderate concentrations, ROS are necessary for a number of protective reactions. Thus, ROS are essential mediators of antimicrobial phagocytosis, detoxification reactions carried out by the cytochrome P-450 complex, and apoptosis which eliminates cancerous and other life-threatening cells. Excessive antioxidants could dangerously interfere with these protective functions, while temporary depletion of antioxidants can enhance anti-cancer effects of apoptosis. Experimental data are presented supporting these notions. The human population is heterogeneous regarding ROS levels. Intake of exogenous antioxidants (vitamins E, C, beta-carotene and others) could protect against cancer and other degenerative diseases in people with innate or acquired high levels of ROS. However, abundant antioxidants might suppress these protective functions, particularly in people with a low innate baseline level of ROS. Screening human populations for ROS levels could help identify groups with a high level of ROS that are at a risk of developing cancer and other degenerative diseases. It also could identify groups with a low level of ROS that are at a risk of down-regulating ROS-dependent anti-cancer and other protective reactions. Screening populations could provide a scientifically grounded application of antioxidant supplements, which could significantly contribute to the nation's health.

Renal cell carcinoma risk associated with lower intake of micronutrients

“…Selenium plays critical roles in major metabolic pathways, and is an essential element to protect the body from harmful substances. Recent studies demonstrated that selenium supplementation reduces side effects from chemotherapy and improves kidney and liver functions in cancer patients 16, 19, 20. Analysis of selenium intake by participants in our study revealed inverse associations with RCC risk for both EA and AA, with greater protective effects among AA.…”

“…Many vitamins from diet and supplements, including vitamin A, C, and B, have been shown to have antioxidative effects and may influence RCC risk 5, 6, 7, 8, 14, 15. Intake of dietary E vitamins, including α‐, β‐, δ‐, and γ‐tocopherol, is suggested to be chemo‐preventative 16. Supplementation with selenium may influence RCC risk, and selenium has been shown to possess anti‐tumor functions 17, 18, 19, 20.…”

High-dose vitamin C supplement use is associated with self-reported histories of breast cancer and other illnesses in the UK Women’s Cohort Study

“…Despite controversy surrounding evidence of benefits of high-dose vitamin C supplementation for prolonged cancer survival (32)(33)(34) , our results showed prior to seasonal weighting that women with any type of cancer were more likely to be high-dose vitamin C supplement takers than women with no history of cancer. Since antioxidants can potentially reduce the effectiveness of anti-cancer drugs (35,36) , patients should be encouraged to discuss their supplement use with their doctors in order to avoid contraindications. For some cancer patients, supplement use may be a coping behaviour and a way of taking control (37,38) .…”

Conceitos atuais e perspectivas na prevenção da degeneração macular relacionada à idade

“…Espéci-es reativas de oxigênio, em moderada concentração, são mediadores essenciais de reações pelas quais o corpo livra-se de células indesejáveis. Sendo suplementos antioxidantes redutores de radicais livres, provavelmente ocorra interferência nos mecanismos essenciais de defesa para livrar o organismo das células defeituosas, incluindo aquelas que são pré-cancerosas e cancerosas (24) . Sendo assim, suplementos vitamínicos podem ser nocivos (19)(20)(21)(22)(23)25) .…”

“…Por outro lado, depois de décadas de uso para prevenir e combater doenças sistêmicas, vários relatos demonstram que o uso indiscriminado de antioxidantes pode ser extremamente maléfico à saúde (19)(20)(21)(22)(23)(24)(25)(26)(27) .…”