Supplement

Selenium

Selenium is a trace mineral the body uses for antioxidant enzymes and for converting thyroid hormone to its active form. People mostly look at it for Kashin-Beck disease, a bone and joint disorder where low selenium is a major contributing factor, and the evidence for that use is strong. For Hashimoto's thyroiditis, however, studies of 1,377 people found no clear difference in signs, and that evidence is very limited.

Updated 30 September 2026
How we grade
6 studies cited

Best evidence: Grade B
Conditions studied: 8
Outcomes: 29
Graded outcomes: 0132

Evidence by condition

Strong
Moderate
Limited
Very limited

8 conditions

Gestational Diabetes

Gestational Diabetes: outcomes studied for Selenium
Grade	Outcome	Effect	Size	Studies	People
	Bilirubin Moderate Decrease	Improves (the measure goes down)	Moderate effect		106 people
	Insulin Resistance	Improves (the measure goes down)		1 study	175 people
Studies that measured insulin resistance Selenium supplementation for management of gestational diabetes mellitus in pregnancy: a systematic review and meta-analysis of randomized controlled trials.BMC Endocr Disord · PMID 41073938
	Triglycerides	Improves (the measure goes down)		1 study	121 people
Studies that measured triglycerides Effect of selenium supplementation on hemodialysis patients: a meta-analysis.Int Urol Nephrol · PMID 39900786
	Blood glucose	Improves (the measure goes down)			175 people
	High-density lipoprotein (HDL)	Improves (the measure goes up)			121 people
	Low-density lipoprotein (LDL)	Improves (the measure goes down)			121 people
	Total cholesterol	Improves (the measure goes down)			121 people

Acne

Acne: outcomes studied for Selenium
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Acne Symptoms Small Improvement	Improves (the measure goes down)	Small effect		56 people

Migraine Headache

Migraine Frequency: improves
Migraine Severity: improves
Nitric Oxide: improves

Migraine Headache: outcomes studied for Selenium
Outcome	Effect	Size	People
Migraine Frequency Small Decrease	Improves (the measure goes down)	Small effect	72 people
Migraine Severity	Improves (the measure goes down)		72 people
Nitric Oxide	Improves (the measure goes up)		72 people

Pain Relief

Migraine Frequency: improves
Migraine Severity: improves
Nitric Oxide: improves

Pain Relief: outcomes studied for Selenium
Outcome	Effect	Size	People
Migraine Frequency Small Decrease	Improves (the measure goes down)	Small effect	72 people
Migraine Severity	Improves (the measure goes down)		72 people
Nitric Oxide	Improves (the measure goes up)		72 people

Chronic Kidney Disease (CKD)

Body Mass Index (BMI)
Triglycerides: improves
C-Reactive Protein (CRP): improves

Chronic Kidney Disease (CKD): outcomes studied for Selenium
Grade	Outcome	Effect	Size	Studies	People
	Body Mass Index (BMI) No effect		NoneNo effect		2,080 people
	Triglycerides	Improves (the measure goes down)		1 study	2,080 people
Studies that measured triglycerides Effect of selenium supplementation on hemodialysis patients: a meta-analysis.Int Urol Nephrol · PMID 39900786
	C-Reactive Protein (CRP)	Improves (the measure goes down)			2,080 people
	Ferritin	Improves (the measure goes up)			2,080 people
	Hemoglobin	Improves (the measure goes up)			2,080 people
	High-density lipoprotein (HDL)	Improves (the measure goes up)			2,080 people
	Low-density lipoprotein (LDL)	Improves (the measure goes down)			2,080 people
	Total cholesterol	Improves (the measure goes down)			2,080 people

Hashimoto's disease

Hashimoto's Thyroiditis Signs
Thyroid-Stimulating Hormone: improves
Serum T3: improves

Hashimoto's disease: outcomes studied for Selenium
Grade	Outcome	Effect	Size	Studies	People
	Hashimoto's Thyroiditis Signs No effect		NoneNo effect		1,377 people
	Thyroid-Stimulating Hormone	Improves (the measure goes up)		1 study	939 people
Studies that measured thyroid-stimulating hormone Clinical efficacy of selenium supplementation in patients with Hashimoto thyroiditis: A systematic review and meta-analysis.Medicine · PMID 40898469
	Serum T3	Improves (the measure goes up)			432 people
	Serum T4	Improves (the measure goes up)			776 people
	Subjective Well-Being	Improves (the measure goes up)			171 people

General Cardiovascular Health

Pre-Eclampsia Risk: changes; see studies

General Cardiovascular Health: outcomes studied for Selenium
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Pre-Eclampsia Risk	Changes; see studies		3 studies	230 people
Studies that measured pre-eclampsia risk Selenium and Preeclampsia: a Systematic Review and Meta-analysisBiol Trace Elem Res · 2016 · PMID 26516080 Selenium supplementation and the incidence of preeclampsia in pregnant Iranian women: a randomized, double-blind, placebo-controlled pilot trialTaiwan J Obstet Gynecol · PMID 20708525 Effect of selenium on markers of risk of pre-eclampsia in UK pregnant women: a randomised, controlled pilot trialBr J Nutr · PMID 24708917

Preeclampsia

Pre-Eclampsia Risk: changes; see studies

Preeclampsia: outcomes studied for Selenium
Grade	Outcome	Effect	Size	Studies	People	Studies list
	Pre-Eclampsia Risk	Changes; see studies		3 studies	166 people
Studies that measured pre-eclampsia risk Selenium and Preeclampsia: a Systematic Review and Meta-analysisBiol Trace Elem Res · 2016 · PMID 26516080 Selenium supplementation and the incidence of preeclampsia in pregnant Iranian women: a randomized, double-blind, placebo-controlled pilot trialTaiwan J Obstet Gynecol · PMID 20708525 Effect of selenium on markers of risk of pre-eclampsia in UK pregnant women: a randomised, controlled pilot trialBr J Nutr · PMID 24708917

What the published studies found

1 automated reading

Automated reading of the published studies (Decosa evidence engine), for outcomes Dr. Grey has not graded yet. It is not a Dr. Grey grade and does not change one. How it is read

Respiratory infections
The studies read are too weak to tell whether Selenium changes respiratory infections. The strongest review read studied critically ill adults. The evidence is very weak.
6 studies counted of 11 read: 4 reviews and 2 trials (159 people in the trials).
1. Meta-analysis, 2015; 16 studies, 2,084 people; critically ill adults: unclear: evidence too weak to tell (the review the verdict rests on). Selenium supplementation for critically ill adultsPubMed 26214143
2. Systematic review, 2020; 43 studies; humans with viral and respiratory infections: improves. selenium and zinc have also shown favourable immune-modulatory effects Enhancing immunity in viral infections, with special emphasis on COVID-19: A reviewPubMed 32334392
3. Meta-analysis, 2019; 13 studies; patients with sepsis syndrome: no clear difference. incidence of renal failure, secondary infection or duration A meta-analysis of randomized controlled trials: Efficacy of selenium treatment for sepsisPubMed 30817625
4. Meta-analysis, 2016; 21 studies: no clear difference. no significant treatment effect of parenteral Se High-dose intravenous selenium does not improve clinical outcomes in the critically ill: a systematic review and meta-analysisPubMed 27788688
5. Randomised trial, 2025; 60 people; hospitalised under-five children with acute lower respiratory tract infections: improves. reduces the need for mechanical ventilation Oral Selenium as an Adjunct in the Treatment of Acute Lower Respiratory Tract Infections in Children: A Double-Blind Randomized Controlled TrialPubMed 40202578
6. Randomised trial, 2018; 99 people: no clear difference. The incidence of VAP was 19.4/1000days of mechanical ventilation in the placebo group while it … Antioxidant reserve of the lungs and ventilator-associated pneumonia: A clinical trial of high dose selenium in critically ill patientsPubMed 29288963
Automated reading of the published studies (Decosa evidence engine), run 30 Sep 2026. It reads abstracts, can miss studies, and a repeat run can differ.

Key findings

BilirubinGestational DiabetesImproves (the measure goes down)
Acne SymptomsAcneImproves (the measure goes down)
Migraine FrequencyMigraine HeadacheImproves (the measure goes down)

Shop the evidence-backed picks

Third-party tested Selenium products, in the forms the graded studies used where we can match them.

Grade B

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Studies cited

6 studies from PubMed

Selenium and Preeclampsia: a Systematic Review and Meta-analysisBiol Trace Elem Res, 2016 · PMID 26516080
Selenium supplementation and the incidence of preeclampsia in pregnant Iranian women: a randomized, double-blind, placebo-controlled pilot trialTaiwan J Obstet Gynecol · PMID 20708525
Effect of selenium on markers of risk of pre-eclampsia in UK pregnant women: a randomised, controlled pilot trialBr J Nutr · PMID 24708917
Effect of selenium supplementation on hemodialysis patients: a meta-analysis.Int Urol Nephrol · PMID 39900786
Clinical efficacy of selenium supplementation in patients with Hashimoto thyroiditis: A systematic review and meta-analysis.Medicine · PMID 40898469
Selenium supplementation for management of gestational diabetes mellitus in pregnancy: a systematic review and meta-analysis of randomized controlled trials.BMC Endocr Disord · PMID 41073938