Selenium
Selenium (Selenomethionine)
Essential trace mineral critical for thyroid function, antioxidant defense, and immune health.
Selenium is an essential trace mineral required for the production of selenoproteins, which have antioxidant and thyroid-regulating functions. Deficiency is uncommon in most developed countries, but suboptimal levels may affect thyroid function and immune health. Supplementation is most beneficial for those with low selenium status.
Mechanisms of Action
Selenoprotein Synthesis
Required to make crucial antioxidant enzymes
Thyroid Support
Critical for thyroid hormone metabolism
Recommended Dose
100-200mcg
Optimal Timing
- With food
Take with food
Best Form
Selenomethionine (best absorbed)
Alternatives: Selenium yeast, Sodium selenite
Selenomethionine is the most bioavailable organic form.
Duration
Minimum: 4 weeks
Optimal: weeks
Cycling: Not required
Note: Take with food for better absorption. Do not exceed 400mcg/day from all sources.
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Thyroid Support
Supports healthy thyroid hormone levels
Immune Function
Supports immune cell activity
Safe at RDA levels; don't exceed 400mcg
Who Should NOT Take This
- Those with adequate/high selenium status
- Thyroid conditions (hypothyroidism, hyperthyroidism, Hashimoto's, Graves' disease) — selenium affects thyroid hormone metabolism and may alter thyroid function; consult endocrinologist before use
Drug Interactions
May interact; consult oncologist
May affect cholesterol-lowering effects
Possible Side Effects
Tip: Take with food
Tip: Reduce dose
Tip: Stop supplementation; indicates excess
Warnings
- Narrow therapeutic window — toxicity possible at high doses
- Signs of excess: garlic breath, hair loss, nail changes
- Test levels before supplementing if uncertain
Vitamin C
complementaryBoth support immune function and antioxidant defense
Enhanced immune and antioxidant support
Iodine
essentialSelenium is required for thyroid hormone conversion
Optimal thyroid function — don't supplement iodine without adequate selenium
Vitamin E
complementaryBoth support glutathione antioxidant system
Enhanced antioxidant defense
Top studies from 40+ peer-reviewed papers
Jenkins DJA et al. • The American journal of clinical nutrition (2020)
“The addition of selenium should be considered for supplements containing antioxidant mixtures if they are to be associated with CVD and all-cause mortality risk reduction.”
Key Findings:
- However, a decreased risk with antioxidant mixtures was seen for CVD mortality when selenium was part of the mix (RR: 0.77; 95% CI: 0.62, 0.97; P = 0.02), with no association when selenium was absent.
- Similarly, when selenium was part of the antioxidant mixture, a decreased risk was seen for all-cause mortality (RR: 0.90; 95% CI: 0.82, 0.98; P = 0.02) as opposed to an increased risk when selenium was absent (RR: 1.09; 95% CI: 1.04, 1.13; P = 0.0002).
- The addition of selenium should be considered for supplements containing antioxidant mixtures if they are to be associated with CVD and all-cause mortality risk reduction.
- This trial was registered at https://www.crd.york.ac.uk/PROSPERO/ as CRD42019138268.
Vinceti M et al. • The Cochrane database of systematic reviews (2018)
“Well-designed and well-conducted RCTs have shown no beneficial effect of selenium supplements in reducing cancer risk (high certainty of evidence).”
Key Findings:
- For analyses of RCTs with low risk of bias, the summary risk ratio (RR) for any cancer incidence was 1.01 (95% confidence interval (CI) 0.93 to 1.10; 3 studies, 19,475 participants; high-certainty evidence).
- The RR for estimated cancer mortality was 1.02 (95% CI 0.80 to 1.30; 1 study, 17,444 participants).
- Selenium supplementation did not reduce overall cancer incidence (RR 0.99, 95% CI 0.86 to 1.14; 5 studies, 21,860 participants) nor mortality (RR 0.81, 95% CI 0.49 to 1.32; 2 studies, 18,698 participants).
- As RCT participants have been overwhelmingly male (88%), we could not assess the potential influence of sex or gender.We included 15 additional observational cohort studies (70 in total; over 2,360,000 participants).
Hurst R et al. • The American journal of clinical nutrition (2012)
“The relation between selenium status and decreased prostate cancer risk was examined over a relatively narrow range of selenium status; further studies in low-selenium populations are required.”
Key Findings:
- Three high-quality studies included in the meta-analysis of toenail selenium and cancer risk indicated a reduction in prostate cancer risk (estimated RR: 0.29; 95% CI: 0.14, 0.61) with a toenail selenium concentration between 0.85 and 0.94 μg/g.
- The relation between selenium status and decreased prostate cancer risk was examined over a relatively narrow range of selenium status; further studies in low-selenium populations are required.
- Further research warranted to confirm findings
Huwiler VV et al. • Thyroid : official journal of the American Thyroid Association (2024)
“Indications for lowering TPOAb were found independent of THRT.”
Key Findings:
- We synthesized the results as standardized mean differences (SMD) or odds ratio (OR), assessed risk of bias using the Cochrane RoB 2 tool, and rated the evidence using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach.
- Our meta-analysis found that selenium supplementation decreased TSH in patients without THRT (SMD -0.21 [confidence interval, CI -0.43 to -0.02]; 7 cohorts, 869 participants; I2 = 0%).
- In addition, TPOAb (SMD -0.96 [CI -1.36 to -0.56]; 29 cohorts; 2358 participants; I2 = 90%) and malondialdehyde (MDA; SMD -1.16 [CI -2.29 to -0.02]; 3 cohorts; 248 participants; I2 = 85%) decreased in patients with and without THRT.
- Adverse effects were comparable between the intervention and control groups (OR 0.89 [CI 0.46 to 1.75]; 16 cohorts; 1339 participants; I2 = 0%).
Liang X et al. • Frontiers in immunology (2024)
“Patients with vitiligo should reduce smoking and alcohol consumption and take appropriate vitamin E, B12, copper, and zinc supplements.”
Key Findings:
- Vitamin C [mean difference (MD), -0.342; 95% confidence interval (CI), -1.090-0.407; p >0.05), folic acid (MD, -1.463; 95% CI, -7.133-4.208; p >0.05), and selenium (MD, 0.350; 95% CI, -0.687-1.387; p >0.05) levels did not differ between the groups.
- The serum iron level of the vitiligo group was significantly higher than that of the control group (MD, 1.181; 95% CI, 0.390-1.972; p <0.005).
- Patients with vitiligo should reduce smoking and alcohol consumption and take appropriate vitamin E, B12, copper, and zinc supplements.
- However, vitamin C, vitamin D, selenium, iron, and folic acid supplements are unnecessary.
Study Type Distribution
Goals This Supplement Supports
Related Goals
This information is for educational purposes only and is not intended as medical advice. Always consult a qualified healthcare provider before starting any supplement.