How does the body eliminate selenium?

Selenium Elimination from the Body

The body primarily eliminates selenium through urinary excretion, with approximately 31% of ingested selenium being excreted in urine, predominantly as unmetabolized selenate. 1

Pathways of Selenium Elimination

Primary Elimination Routes

• Urinary excretion: The main pathway for selenium elimination

  • Unmetabolized selenate is the predominant form excreted (approximately 30% of ingested dose) 1
  • Peak elimination occurs approximately 2 hours after selenium ingestion 1
  • Selenium-containing carbohydrates (selenosugars) are also excreted in urine 1, 2

• Fecal excretion: Secondary route of elimination

  • Less significant compared to urinary excretion
  • Primarily eliminates unabsorbed dietary selenium

Metabolic Processing Before Elimination

The liver plays a central role in selenium metabolism and excretion:

• Acts as the central regulatory organ for selenium homeostasis 3
• Produces excretory forms of selenium to regulate whole-body selenium levels 3
• During deficiency, the liver curtails excretion to conserve selenium 3
• Secretes selenoprotein P (Sepp1) into plasma for distribution to tissues based on need 3

Individual Variation in Selenium Excretion

Selenium excretion patterns show important individual differences:

• Trimethylselenonium (TMSe) status: People can be categorized as either TMSe eliminators or non-TMSe eliminators 1

  • TMSe eliminators: Excrete trimethylselenonium in urine and metabolize selenate more extensively
  • Non-TMSe eliminators: Do not excrete TMSe and excrete selenate largely unmetabolized 1

• Consistency in excretion patterns:

  • Modest day-to-day and week-to-week variation within individuals 2
  • More significant variation between individuals 2

Forms of Selenium Excreted in Urine

The main selenium compounds found in urine include:

• Selenate (unmetabolized form) 1
• Selenosugar 1 (methyl-2-acetamido-2-deoxy-1-seleno-β-D-galactopyranoside) 1, 2
• Selenosugar 3 (methyl-2-amino-2-deoxy-1-seleno-β-D-galactopyranoside) 1, 2
• Trimethylselenonium (in TMSe eliminators) 1, 2
• Se-methylselenoneine (consistently detected in all individuals) 2

Factors Affecting Selenium Excretion

Several factors can influence how selenium is eliminated from the body:

• Inflammation: Significantly affects selenium levels and metabolism 4, 5

  • CRP levels of 10-40 mg/L can reduce plasma selenium by 15-25%
  • CRP levels of 41-80 mg/L can reduce plasma selenium by about 35%
  • CRP levels >80 mg/L can reduce plasma selenium by about 50%

• Renal function: The kidneys play a crucial role in selenium excretion

  • N-terminal Sepp1 forms are taken up in the renal proximal tubule by the megalin receptor 3
  • Continuous renal replacement therapy can increase selenium losses 4

• Specific clinical conditions:

  • Burns patients have high losses of selenium 4
  • Patients on renal replacement therapy experience increased selenium elimination 4

Clinical Implications

Understanding selenium elimination is important for:

• Determining appropriate supplementation in deficiency states
• Monitoring patients at risk of deficiency (those on parenteral nutrition, after bariatric surgery, with burns) 5
• Interpreting selenium levels in the context of inflammatory status 4, 5
• Recognizing that plasma selenium <0.4 μmol/L (<32 μg/L) indicates deficiency requiring supplementation 4, 5

The body's selenium regulation mechanisms prioritize vital selenoproteins during deficiency, creating a hierarchy of selenium distribution to maintain essential functions 3.