Selenium

Best for

Build key mineral stores

Large effect, needs confirmation for 3–39 weeks · 2 meta-analyses , n=706

58 papers · 10 claims · 120 outcomes scored · 7 positive

Outcomes

What selenium actually does, by outcome

Each row is one outcome with effect size, evidence base, the dose that worked in trials, and time to first effect. Magnitude tiers come from native-unit MCID where available, Cohen's d otherwise.

Outcome Effect size Evidence Dose Weeks Rank

Calm thyroid autoimmune activity Likely strong benefit

Reduces the antibodies that attack thyroid tissue in Hashimoto's.

9 meta-analyses n=5.1k 50–1000 mcg 8–52 wk #1/3

25524327·32676110·33650299·34909430 +5 more

large

9 meta-analyses n=5.1k Meta-analyzed I²=95%

50–1000 mcg

8–52 wk

#1 /3

Reduce oxidative cell damage Large effect, needs confirmation

Less oxidative damage to your cell membranes, proteins, and DNA.

11 meta-analyses n=2.3k 60–400 mcg 8–52 wk #2/30

19033020·24938534·32676110·35224710 +7 more

large

11 meta-analyses n=2.3k Meta-analyzed I²=85%

60–400 mcg

8–52 wk

#2 /30

Build key mineral stores Large effect, needs confirmation

Essential mineral blood levels rise into optimal range, confirming absorption.

11 meta-analyses n=706 0.054–500 mg 3–39 wk #2/5

19033020·24708917·24938534·30215171 +7 more

large

11 meta-analyses n=706 Meta-analyzed

0.054–500 mg

3–39 wk

#2 /5

Strengthen sperm count and motility Proven benefit

Raises count, movement, and normal shape in your semen analysis.

2 meta-analyses n=2.2k 100–200 mcg 19–22 wk #1/6

31160241·35265037

moderate

2 meta-analyses n=2.2k Meta-analyzed I²=79%

100–200 mcg

19–22 wk

#1 /6

Improve thyroid hormone balance Likely modest benefit

Keeps the gland that controls your metabolism producing at the right level.

7 meta-analyses n=4.7k 80–1000 mcg 5–52 wk #1/3

27683225·32676110·34909430·38243784 +3 more

small

7 meta-analyses n=4.7k Meta-analyzed I²=89%

80–1000 mcg

5–52 wk

#1 /3

Lower your blood pressure Faint early signal

Brings down both systolic and diastolic, especially when baseline runs high.

3 RCTs n=155 200 mcg 8–12 wk

35047136·35224710·38757125

small

3 RCTs n=155

200 mcg

8–12 wk

—

Lower prostate cancer risk Not enough research

Fewer diagnoses, slower precancerous changes, steadier PSA.

4 meta-analyses n=37k 200–400 mcg 156–284 wk #4/5

19066370·22887343·24683040·28415774

trivial

4 meta-analyses n=37k Meta-analyzed

200–400 mcg

156–284 wk

#4 /5

Ease low thyroid symptoms Probably doesn't help

Reduces cold intolerance, fatigue, and brain fog from underactive thyroid.

1 meta-analysis n=679 80–200 mcg —

27683225

large

1 meta-analysis n=679 Meta-analyzed

80–200 mcg

—

Protect thyroid function in pregnancy Faint negative signal

Keeps your thyroid stable when pregnancy doubles its workload.

1 RCT n=31 60 mcg —

25524327

small

1 RCT n=31

60 mcg

—

Lower non-melanoma skin cancer risk Not enough research

Repairs sun-damaged skin cells before they turn precancerous.

1 meta-analysis n=— — —

24683040

—

1 meta-analysis n=— Meta-analyzed

—

Outcome	Effect	Evidence	Dose	Weeks	Rank
Calm thyroid autoimmune activity Likely strong benefit	large	9 meta-analyses n=5.1k Meta-analyzed	50–1000 mcg	8–52 wk	#1/3
Reduce oxidative cell damage Large effect, needs confirmation	large	11 meta-analyses n=2.3k Meta-analyzed	60–400 mcg	8–52 wk	#2/30
Build key mineral stores Large effect, needs confirmation	large	11 meta-analyses n=706 Meta-analyzed	0.054–500 mg	3–39 wk	#2/5
Strengthen sperm count and motility Proven benefit	moderate	2 meta-analyses n=2.2k Meta-analyzed	100–200 mcg	19–22 wk	#1/6
Improve thyroid hormone balance Likely modest benefit	small	7 meta-analyses n=4.7k Meta-analyzed	80–1000 mcg	5–52 wk	#1/3
Lower your blood pressure Faint early signal	small	3 RCTs n=155	200 mcg	8–12 wk	—
Lower prostate cancer risk Not enough research	trivial	4 meta-analyses n=37k Meta-analyzed	200–400 mcg	156–284 wk	#4/5
Ease low thyroid symptoms Probably doesn't help	large	1 meta-analysis n=679 Meta-analyzed	80–200 mcg	—	—
Protect thyroid function in pregnancy Faint negative signal	small	1 RCT n=31	60 mcg	—	—
Lower non-melanoma skin cancer risk Not enough research		1 meta-analysis n=— Meta-analyzed	—	—	—

Buy well

Recommended Selenium products

Real products that dose Selenium where the research does, in a clean formulation, from brands we've audited. We only list ones we'd stand behind.

Chosen for adequate Selenium dosing vs. the studied range, a clean formulation (grade A–C), and independent brand-quality audits. Not sponsored.

Risk profile

Adverse events and known drug interactions

Safety events

grade 3 or 4 adverse events severe

ovarian torsion requiring right oophorectomy severe

prostate cancer diagnosis severe

Non-ST elevation myocardial infarction (serious adverse event) severe

Diagnosis of bowel cancer (serious adverse event) severe

Pulmonary embolus due to metastatic bowel cancer (serious adverse event) severe

nausea moderate

elevated PSA moderate

Drug interactions

Epirubicin major increases effect

Lipid Modifying Agents major increases toxicity

5-Fluorouracil moderate increases effect

Gemcitabine moderate increases effect

Cisplatin moderate increases effect

Paclitaxel moderate increases effect

Simvastatin moderate decreases effect

Roxadustat moderate decreases concentration

Lithium minor decreases effect

Lipid Modifying Agents minor unknown

Sources

Generated August 14, 2026

Selenium

What selenium actually does, by outcome

Recommended Selenium products

Adverse events and known drug interactions

More evidence for Selenium

Moonlight and Razor's Edge: Selenium's U-Shaped Lesson from Rural China to Your Kitchen

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Brazil nut

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Selenium

Recommended Selenium products

More evidence for Selenium

NewMoonlight and Razor's Edge: Selenium's U-Shaped Lesson from Rural China to Your Kitchen

NewBest Supplements for Depression, Ranked by Clinical Evidence

NewBest Supplements for Migraines and Headaches, Ranked by Clinical Evidence

NewBest Supplements to Lower Blood Pressure in Pregnancy (2026)

NewBrazil nut

NewAlpha Lipoic Acid

Moonlight and Razor's Edge: Selenium's U-Shaped Lesson from Rural China to Your Kitchen

Best Supplements for Depression, Ranked by Clinical Evidence

Best Supplements for Migraines and Headaches, Ranked by Clinical Evidence

Best Supplements to Lower Blood Pressure in Pregnancy (2026)

Brazil nut

Alpha Lipoic Acid