{"entity":{"id":"selenium-supplements","kind":"technology","name":"Selenium supplements","aka":["Selenite","Selenomethionine","Selenate"],"tldr":"Selenium is an essential trace mineral sold to prevent cancer. The large SELECT trial found it did not prevent prostate cancer or bowel polyps, other studies suggest long-term use may raise the risk of some skin cancers and of dying from prostate cancer, and overdoses have killed.","summary":"Selenium is needed in small amounts for antioxidant enzymes and thyroid function and is found in seafood, meat, grains and nuts. Memorial Sloan Kettering's About Herbs summary sets out why it is no longer considered a cancer preventive: the Selenium and Vitamin E Cancer Prevention Trial (SELECT) found no protection against prostate cancer or colorectal adenomas; selenium with soy and vitamin E did not slow prostate cancer progression; a review of randomised trials found no clear preventive effect; a chemoprevention trial after non-small-cell lung cancer showed no benefit and a possible, non-significant increase in second lung cancers; and long-term supplementation may increase some skin cancers and, in one analysis, prostate cancer mortality. A few studies suggest selenium may reduce some treatment side effects, including diarrhoea and lymphoedema of the head and neck, but MSK advises that supplementation during treatment be guided by the clinical team. Toxicity is real: chronic intake above 1000 micrograms a day causes selenosis (nail and hair loss, neuropathy, liver damage), and a 75-year-old man died after taking 10 g of sodium selenite to treat his own prostate cancer after reading about it online.","status":"negative","asOf":"2026-11-04","links":[{"label":"MSK About Herbs: Selenium (page last updated 15 December 2021)","url":"https://www.mskcc.org/cancer-care/integrative-medicine/herbs/selenium"},{"label":"NCI PDQ: Prostate cancer, nutrition and dietary supplements","url":"https://www.cancer.gov/about-cancer/treatment/cam/hp/prostate-supplements-pdq"}],"tags":["complementary","supportive-care","evidence:no-benefit"],"related":["lycopene","coenzyme-q10"],"cancers":["prostate","colorectal","nsclc"],"sections":["supportive-care","prevention","nutrition-lifestyle"],"technologies":["integrative-oncology","chemoprevention","dietary-supplements-treatment-interactions"],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":[],"trials":[],"people":[],"bottlenecks":["b-misinformation"],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"principle":"Selenium is incorporated into selenoproteins such as glutathione peroxidase; people who are not deficient gain no further antioxidant protection from extra selenium.","strengths":["Tested in large randomised prevention trials, so the answer is clear"],"limitations":["No cancer prevention in SELECT","Possible increase in skin and prostate cancer outcomes","Toxic in overdose"]},"route":"/technologies/selenium-supplements/","neighbours":{"technology":[{"id":"chemoprevention","kind":"technology","name":"Chemoprevention & risk-reducing surgery","route":"/technologies/chemoprevention/"},{"id":"coenzyme-q10","kind":"technology","name":"Coenzyme Q10","route":"/technologies/coenzyme-q10/"},{"id":"dietary-supplements-treatment-interactions","kind":"technology","name":"Dietary supplements during cancer treatment: interactions and harms","route":"/technologies/dietary-supplements-treatment-interactions/"},{"id":"integrative-oncology","kind":"technology","name":"Evidence-based integrative oncology","route":"/technologies/integrative-oncology/"},{"id":"lycopene","kind":"technology","name":"Lycopene","route":"/technologies/lycopene/"},{"id":"pc-spes","kind":"technology","name":"PC-SPES","route":"/technologies/pc-spes/"}],"cancer":[{"id":"colorectal","kind":"cancer","name":"Colorectal cancer","route":"/cancers/colorectal/"},{"id":"nsclc","kind":"cancer","name":"Non-small-cell lung cancer","route":"/cancers/nsclc/"},{"id":"prostate","kind":"cancer","name":"Prostate cancer","route":"/cancers/prostate/"}],"section":[{"id":"nutrition-lifestyle","kind":"section","name":"Diet, Exercise & Lifestyle","route":"/fronts/nutrition-lifestyle/"},{"id":"prevention","kind":"section","name":"Prevention & Risk","route":"/fronts/prevention/"},{"id":"supportive-care","kind":"section","name":"Supportive Care & Survivorship","route":"/fronts/supportive-care/"}],"bottleneck":[{"id":"b-misinformation","kind":"bottleneck","name":"Misinformation and unproven therapies","route":"/bottlenecks/b-misinformation/"}]}}