What are the benefits of selenium?

Benefits of Selenium

Selenium is an essential trace element that provides critical antioxidant protection, supports thyroid hormone metabolism, enhances immune function, and may reduce mortality in individuals with adequate intake (plasma concentration 1.5-1.9 mmol/L), though supplementation for cancer prevention remains unproven in humans and carries a narrow safety margin. 1

Core Physiological Functions

Selenium serves as a fundamental component of human metabolism through its incorporation into at least 25 selenoproteins as the amino acid selenocysteine. 1 The primary benefits include:

Antioxidant Defense

• Selenium functions as a potent antioxidant through the glutathione peroxidase (GPX) enzyme family, which provides first-line defense against oxidative damage in both extracellular and intracellular environments. 1
• The antioxidant activity stems from selenium's six electrons in its outermost shell, making it an optimal electron donor and receiver. 1
• GPX-1 protects red blood cells while GPX-3 functions in plasma. 1

Thyroid Hormone Regulation

• Selenium-containing iodothyronine deiodinase enzymes control thyroid hormone metabolism, converting the prohormone thyroxine (T4) to active triiodothyronine (T3). 2
• This function is essential for proper metabolic regulation throughout the body. 2

Immune System Support

• Selenoproteins regulate immune function and inflammatory responses, with selenium deficiency impairing healthy immune responses. 3, 2
• Selenium demonstrates anti-inflammatory and antiviral properties through its role in selenoprotein synthesis. 4

Cellular Protection

• Selenoproteins control cell proliferation and apoptosis, contributing to cellular health and potentially reducing retroviral virulence. 1
• Emerging evidence suggests selenium may protect vascular endothelium. 1

Recommended Intake Levels

Daily oral selenium intake should range between 50-70 mcg/day for most individuals, with requirements varying based on specific health goals. 1

• Minimum requirement: 20 mcg/day - prevents Keshan disease (selenium deficiency cardiomyopathy). 1
• Standard recommendation: 50-70 mcg/day - meets basic physiological needs. 1
• Upper range: 90 mcg/day - maximizes plasma and whole blood glutathione peroxidase activity. 1
• For parenteral nutrition: 60-100 mcg/day IV brings plasma concentration into target range. 1

Optimal Plasma Concentrations

• Plasma selenium concentration of 1.20 mmol/L saturates plasma GPX-3 activity. 1
• Plasma concentration of 1.5-1.9 mmol/L may be closer to optimal for reducing mortality in free-living individuals, though levels sufficient to saturate GPX-3 may be insufficient to optimize immune response and reduce cancer risk. 1

Cancer Prevention: Equivocal Evidence

The evidence regarding selenium's role in cancer prevention remains mixed and inconclusive:

Animal Studies vs. Human Evidence

• Animal studies suggest selenium protects against cancer, but human studies have yielded inconsistent results. 1
• One experimental trial showed selenium supplements might reduce risk of lung, colon, and prostate cancers, but the American Cancer Society emphasizes that repeated and well-controlled studies are needed to confirm these findings. 1
• The 2006 American Cancer Society guidelines note that selenium intake sufficient to saturate GPX-3 activity may be insufficient to optimize cancer risk reduction. 1

Critical Safety Consideration

High-dose selenium supplements are not recommended due to the narrow margin between safe and toxic dosages. 1 The maximum supplemental dose should not exceed 200 micrograms per day. 1

Additional Health Benefits

Reproductive Health

• Selenium plays a significant role in male fertility, with deficiency causing deterioration in semen quality and sperm motility. 5
• Sperm capsule selenoprotein stabilizes the integrity of sperm flagella. 2
• Low selenium concentration in early pregnancy predicts low birth weight, and deficiency may lead to gestational complications and miscarriages. 5

Cardiovascular Protection

• Selenium may decrease cardiovascular disease mortality through its antioxidant and vascular protective effects. 2

Protection Against Heavy Metals

• Selenium protects against detrimental effects of heavy metals in the body. 5

Absorption and Dietary Sources

• Selenium is well absorbed from the digestive tract (56-81%) with low inter-individual variation. 1
• The form of selenium and food constituents are key determinants of post-absorptive metabolism. 1
• Good dietary sources include seafood, meats, and grain products. 1

Critical Clinical Caveats

Supplementation Not Routinely Recommended

There is no evidence that selenium supplements can reduce cancer risk in the general population, and the few human studies attempting to demonstrate this have yielded disappointing results. 1

Individualized Assessment Required

• Both beneficial and toxic effects of selenium have been reported, with effects strictly dependent on chemical form and concentration. 4
• There is a relatively narrow window between selenium deficiency and toxicity. 4
• Growing evidence suggests selenium health effects depend greatly on baseline levels, requiring an individualized approach to supplementation. 4

Geographic Variation

Because selenium concentrations in blood are affected by dietary intake, which varies by geographic region and soil content, reference intervals should be locally established. 1