tuneTypical Dose
55–200 mcg per day
Mineral
Selenium
Selenium (Se, element 34)
Evidence TierAWADA NOT PROHIBITED
watchEffect Window
3–6 months for thyroid autoantibody reduction; weeks for serum selenium normalization.
check_circleCompliance
WADA NOT PROHIBITED
Overview
Clinical Summary
Selenium is a trace mineral required for thyroid hormone metabolism and antioxidant selenoproteins. It is used to correct low selenium status and to support thyroid autoimmunity biomarkers in selected contexts.
Correcting low selenium supports thyroid hormone conversion and antioxidant defenses. In some Hashimoto’s studies, selenium reduces thyroid autoantibody levels and may improve well-being, though clinical outcomes vary. It can also support sperm quality biomarkers in low-status populations. Minority benefits include mood and oxidative stress improvements. Excess selenium is toxic, so benefits depend on correcting deficiency rather than high dosing.
Essential component of selenoproteins including glutathione peroxidase (antioxidant defense), thioredoxin reductase (redox regulation), and iodothyronine deiodinases (T4→T3 thyroid hormone conversion). Benefits are strongly dependent on baseline selenium status.
Outcomes
What This Is Expected To Influence
Primary Outcomes
- Essential for selenoprotein enzymes (glutathione peroxidase, thioredoxin reductase, iodothyronine deiodinases , T4→T3 conversion)
- Reduces TPOAb in Hashimoto's thyroiditis
- SELECT trial disproved prostate cancer prevention hypothesis in selenium-sufficient men
Secondary Outcomes
- Supports immune function via selenoprotein P
- Antioxidant defense via glutathione peroxidase pathway
- Possible type 2 diabetes risk signal with excess supplementation
Safety
Contraindications and Interactions
Contraindications
- Non-melanoma skin cancer history
- Pregnancy/lactation without medical supervision
Side effects
- GI upset
- Garlic breath/body odor
- Metallic taste
- Hair thinning at high doses
- Selenosis at >400 mcg/day
Interactions
- Statins (possible reduced efficacy , debated)
- Cisplatin/platinum chemotherapy
- Warfarin (monitor INR)
- High-dose vitamin C (reduces selenite absorption)
Avoid if
- Selenium-sufficient status without deficiency indication
- Non-melanoma skin cancer history
- Wilson's disease
Evidence
Study-level References
selenium-SRC-001Meta-analysis
Sourceopen_in_newToulis KA et al. (2010) meta-analysis on selenium supplementation in Hashimoto's thyroiditis.
Population: Adults with Hashimoto's thyroiditis
Dose protocol: Commonly 200 mcg/day selenium (frequently selenomethionine) over 3–6 months
Key findings: Significant reduction in TPOAb compared with controls in Hashimoto's cohorts. Stronger clinical utility signal in low-selenium populations; caution in selenium-replete users due to toxicity and possible glycemic risk at excess exposure.
Notes: Evidence supports targeted use with monitoring; not a blanket population-wide supplementation strategy.
Paper content
Significant reduction in TPOAb compared with controls in Hashimoto's cohorts. Stronger clinical utility signal in low-selenium populations; caution in selenium-replete users due to toxicity and possible glycemic risk at excess exposure.
selenium-SRC-002Randomized controlled trial (n=35,533)
Sourceopen_in_newLippman SM et al. (2009) Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). JAMA.
Population: Healthy men aged ≥50 (≥55 for Black men), selenium-sufficient at baseline
Dose protocol: 200 mcg/day L-selenomethionine vs placebo, median follow-up 5.46 years
Key findings: No reduction in prostate cancer risk (HR 1.04; 99% CI 0.83–1.30). Non-significant increase in prostate cancer with selenium alone (HR 1.04) and in type 2 diabetes with selenium (HR 1.07, p=0.16). Trial stopped early for futility and possible harm signal.
Notes: SELECT is the definitive trial that reversed the NPC-era optimism about selenium for cancer prevention.
Paper content
No reduction in prostate cancer risk (HR 1.04; 99% CI 0.83–1.30). Non-significant increase in prostate cancer with selenium alone (HR 1.04) and in type 2 diabetes with selenium (HR 1.07, p=0.16). Trial stopped early for futility and possible harm signal.
selenium-SRC-003Randomized controlled trial (NPC trial)
Sourceopen_in_newClark LC et al. (1996) Effects of selenium supplementation for cancer prevention in patients with carcinoma of the skin. JAMA.
Population: Adults with history of non-melanoma skin cancer (selenium-deficient southeastern US)
Dose protocol: 200 mcg/day high-selenium yeast vs placebo
Key findings: Reduced total cancer incidence, lung cancer, colorectal cancer, and prostate cancer in a selenium-deficient population. Increased non-melanoma skin cancer recurrence. These benefits were NOT replicated in the selenium-sufficient SELECT population.
Notes: The NPC trial started the selenium-cancer-prevention hypothesis that SELECT ultimately disproved for selenium-sufficient populations.
Paper content
Reduced total cancer incidence, lung cancer, colorectal cancer, and prostate cancer in a selenium-deficient population. Increased non-melanoma skin cancer recurrence. These benefits were NOT replicated in the selenium-sufficient SELECT population.
selenium-SRC-004Phase 3, double-blind, parallel group, randomized controlled pilot study.
Sourceopen_in_newYim GW, Han KH, Lee ST, et al. Efficacy and safety of intravenous administration of high-dose selenium for preventing chemotherapy-induced peripheral neuropathy in platinum-sensitive recurrent ovarian cancer. BMC Med. 2026;24(1):131. doi:10.1186/s12916-026-04637-x. PMID:41630017.
Population: Women with platinum-sensitive recurrent ovarian cancer receiving chemotherapy.
Dose protocol: IV sodium selenite 2000 mcg before each chemotherapy cycle versus placebo
Key findings: Primary endpoint of reducing grade 1+ neuropathy not met. Secondary analysis showed lower grade 2 and motor neuropathy in selenium group during earlier cycles, especially in patients aged 60+. No selenium-related toxicity.
Notes: Exploratory motor neuropathy benefit only. Does not establish selenium as standard neuroprotective intervention during chemotherapy.
Paper content
This double-blind randomized pilot trial tested high-dose intravenous selenium (2000 mcg sodium selenite) before chemotherapy in 68 women with platinum-sensitive recurrent ovarian cancer. The primary endpoint of reducing overall grade 1+ neuropathy was not met. However, a secondary analysis found significantly lower grade 2 and motor neuropathy incidence in the selenium group during earlier treatment cycles, particularly among patients aged 60 and older. No selenium-related toxicity occurred. Quality of life did not differ between groups. The trial provides a safety signal and exploratory motor neuropathy benefit but does not establish selenium as a standard neuroprotective intervention during chemotherapy.
selenium-SRC-005Multicountry observational analysis within a preconception trial.
Sourceopen_in_newGilley SP, Westcott JL, Kemp JF, et al. A Multicountry Analysis of Maternal Selenium Status in Pregnancy and Lactation and Infant Birth Outcomes. J Nutr. 2026;156(2):101279. doi:10.1016/j.tjnut.2025.101279. PMID:41461273.
Population: Pregnant women from Guatemala, India, and Pakistan enrolled in the Women First trial.
Dose protocol: Observational analysis of maternal selenium status across pregnancy and postpartum in Guatemala, India, and Pakistan
Key findings: Selenium declined during pregnancy and was lowest at 3 months postpartum. No significant associations with birth weight, length, head circumference, LBW, SGA, or prematurity. Supplementation did not meaningfully raise serum selenium.
Notes: Adds to the evidence that selenium supplementation does not reliably improve birth outcomes in populations with varied baseline status.
Paper content
This multicountry observational analysis measured serum selenium in pregnant women from Guatemala, India, and Pakistan at multiple timepoints. Selenium levels decreased throughout pregnancy and reached their lowest at 3 months postpartum. The study found no significant associations between maternal selenium status and any measured infant birth outcome, including birth weight, length, head circumference, or rates of low birth weight, small-for-gestational-age, or prematurity. Selenium supplementation within the trial did not meaningfully increase maternal serum levels. The authors suggest larger studies in selenium-deficient populations are needed. This adds to the evidence that selenium supplementation does not reliably improve birth outcomes in populations with varied baseline status.