Selenium

Overview

Selenium is an essential trace element vital for human health. It functions primarily as a cofactor for antioxidant enzymes, especially glutathione peroxidase (GSH-Px) and thioredoxin reductase (TDR), which protect cells from oxidative damage. It is incorporated into selenoproteins in the form of selenocysteine, contributing to antioxidant defense, thyroid hormone regulation, immune support, male reproductive function, and DNA synthesis.

Although this deficiency is rare, maintaining adequate levels is crucial for optimal cellular homeostasis. Interestingly, selenium at nutritional levels acts as an antioxidant and provides chemopreventive effects against cancer, while excess levels may act as pro-oxidants, leading to toxicity. The recommended daily intake for adults is about 55 μg/day, with higher needs during pregnancy (60 μg/day) and lactation (70 μg/day).

It occurs in both organic forms (selenocysteine, selenomethionine) and inorganic forms (selenite, selenate). Major dietary sources include Brazil nuts, seafood, poultry, eggs, meats, dairy products, and grains.

Symptoms

An imbalance, whether deficiency or excess, produces distinct clinical features:

1. Deficiency Symptoms:
   1. Fatigue and muscle weakness
   2. Mental fog and poor cognitive performance
   3. Hair loss and brittle nails
   4. Weak immune function and recurrent infections
   5. Hypothyroidism due to impaired thyroid hormone metabolism
   6. Infertility in both men and women
   7. Disorders linked to deficiency include:
      1. Keshan disease – a cardiomyopathy (heart muscle disease)
      2. Kashin-Beck disease – a form of osteoarthritis affecting joints
2. Toxicity (Selenosis) Symptoms:
   1. Hair loss and nail brittleness
   2. Garlic-like odor on breath
   3. Gastrointestinal upset (nausea, diarrhea, abdominal pain)
   4. Neurological abnormalities such as irritability and nerve dysfunction

Causes

The causes of abnormal levels include both deficiency and excessive exposure:

1. Causes of Selenium Deficiency:
   1. Low dietary intake (endemic in areas with selenium-poor soil)
   2. Malabsorption syndromes
   3. Long-term parenteral nutrition without selenium supplementation
   4. Association with vitamin E deficiency
2. Causes of Selenium Toxicity:
   1. Excessive dietary intake or supplementation
   2. Chronic intake as low as 750 μg/day can be toxic
   3. Occupational or environmental exposure through contaminated soil or water
   4. Inhalation of selenium-containing dust

Risk Factors

Certain individuals and groups are more prone to selenium-related imbalances:

1. Deficiency Risk Factors:
   1. People living in regions with selenium-deficient soil
   2. Patients with chronic gastrointestinal disorders or malabsorption
   3. Individuals on long-term intravenous nutrition without supplementation
   4. People with vitamin E deficiency, as selenium and vitamin E work synergistically
2. Toxicity Risk Factors:
   1. Workers exposed to selenium dust in contaminated industrial areas
   2. Populations relying heavily on selenium-rich diets (e.g., excessive Brazil nut consumption)
   3. Individuals using high-dose supplements beyond recommended allowances
3. Medical Conditions:
   1. Patients with chronic kidney disease or certain cancers may require monitoring of selenium status.

Prevention

The imbalance can be prevented by maintaining optimal intake levels, monitoring supplementation, and ensuring proper dietary habits:

1. Dietary Management:
   1. Incorporate selenium-rich foods such as seafood, poultry, eggs, grains, and Brazil nuts in moderation.
   2. Avoid excessive supplementation unless prescribed by a healthcare provider.
2. Recommended Dietary Allowances (RDA):
   1. Adults: ~55 μg/day
   2. Pregnant women: 60 μg/day
   3. Lactating women: 70 μg/day
3. Testing and Monitoring:
   1. The levels can be assessed using plasma, serum, or urine tests.
   2. Methods include Atomic Absorption Spectroscopy (AAS) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS).
   3. Plasma selenium reference range: 23–190 μg/L.
   4. Urinary selenium testing is useful for detecting both deficiency and toxicity.
4. Sample Handling:
   1. Collect 3 mL of blood in trace element–free tubes (royal blue EDTA or NaHep, or red capped plain tubes).
   2. 24-hour urine samples should be refrigerated and preserved properly during collection.
5. Public Health Strategies:
   1. Educating populations on safe supplementation practices.
   2. Monitoring environmental and occupational exposure in high-risk areas.