Selênio e vitamina E não evitam câncer, mas podem atrapalhar

Mais uma para os adeptos dos suplementos dietéticos, em especial aqueles que usam altas doses de certas vitaminas e micronutrientes sob a cara propaganda de pseudo-especialistas, como os "Terapeutas Ortomoleculares". Lembramos que esta "terapia", muitas vezes ministrada por não médicos sem o menor conhecimento do funcionamento do organismo e do mecanismo das doenças, não é reconhecida pelo Conselho Federal de Medicina nem pelo Ministério da Saúde do Brasil. Desta vez um trabalho tentou associar algum benefício do uso de suplementos de selênio e vitamina E no câncer de próstata, sem resultado. Para piorar, o selênio mostrou uma tendência a associar-se com mutações genéticas que indicam maior gravidade do câncer, com uma significância estatística limítrofe. Embora os autores do estudo tenham responsavelmente se abstido de conclusões precipitadas, fica óbvio que o uso não adequadamente testado de qualquer substância, mesmo suplementos alimentares, pode ser perigoso. Leia mais:

NEW YORK (Reuters Health) Mar 13 - Gene expression profiles in prostatectomy specimens can provide insight into the effects of nutritional supplements taken by those patients preoperatively,
according to the results of a new study.

The study by U.S. researchers is reportedly the first detailed systematic pathological tissue interrogation to be completed inpreoperative patients with favorable-risk prostate cancer. The report appears in the March 4 issue of the Journal of the National Cancer Institute.

Dr. Jeri Kim of the University of Texas M.D. Anderson Cancer Center, Houston, and colleagues note that several major studies and secondary analyses have given contradictory results regarding whether selenium and/or vitamin E reduce the incidence of prostate or other cancers.

To investigate further, the researchers studied 39 men with histologically confirmed adenocarcinoma of the prostate, a life expectancy of at least 10 years and scheduled radical prostatectomy.

The participants were randomly assigned to one of four daily oral regimens: 200 mcg of selenium, 400 IU of vitamin E, a combination of both, or placebo. These treatments were given for 3 to 6 weeks, between enrollment in the study and prostatectomy. Thirty-six participants were included in all parts of the study, including microarray analysis.

The researchers isolated and studied normal, stromal and tumor cells from the biopsy samples. They then identified differential gene expression based on treatment type and also on cell type and tissue zone.

Among other results, an increase in the mean percentage of tumor cells positive for the tumor suppressor p53 in the selenium group (26.3%), compared with that in the placebo group (5%), showed borderline statistical significance (p = 0.051).

In an accompanying editorial, Dr. Eric A. Klein of the Cleveland Clinic Lerner College of Medicine, Ohio, reviews the findings of several major surveys that failed to find cancer-prevention benefits from selenium or vitamin E, and commented that such studies "do not always validate what we believe biology indicates."

He concludes that "dietary or nutrient supplement prevention of cancer may be best achieved by lifelong healthy eating habits."

J Natl Cancer Inst 2009;101:283-285,306-320.