What is Selenium?
Selenium (Se) is a vital trace mineral essential for human health. Discovered in 1818 by Swedish chemist Jöns Jakob Berzelius, it was initially believed to be toxic until its essential biological roles were uncovered. Selenium is crucial for numerous physiological functions, including thyroid hormone metabolism, antioxidant defense, immune responses, and reproductive health.
Forms and Compounds of Selenium
Selenium occurs naturally in both organic and inorganic forms:
Organic Forms:
- Selenomethionine (SeMet): Found in yeast, algae, bacteria, and plants.
- Selenocysteine (SeCys): Present in animal tissues and selenoproteins.
Inorganic Forms:
Selenate (SeO4^2−), Selenite (SeO3^2−), Selenide, and Elemental Selenium.
These forms are incorporated into the body primarily through diet, from foods grown in selenium-rich soils, animal products, seafood, and fortified foods.
Why Do We Need Selenium?
Selenium is indispensable for:
- Thyroid Function: Selenium-dependent enzymes regulate thyroid hormone production and protect the thyroid gland from oxidative damage.
- Immune System: It supports the production of selenoproteins that help combat infections and modulate inflammation.
- Antioxidant Defense: Selenium is a component of glutathione peroxidase, protecting cells from oxidative stress.
- Cancer Prevention: Studies indicate selenium may reduce the risk of prostate, lung, and colon cancers.
- Reproductive Health: Particularly crucial for male fertility, aiding in sperm motility and quality.
- Cognitive Function: Selenium may help reduce the risk of cognitive decline and Alzheimer's disease.
- Metabolic Health: Plays a role in glucose metabolism and may impact Type 2 Diabetes risk.
Uses and Health Benefits of Selenium
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Antioxidant Protection:
Selenium is a key component of antioxidant enzymes like glutathione peroxidase and thioredoxin reductase, neutralizing harmful free radicals. -
Thyroid Health:
The thyroid gland contains the highest amount of selenium per gram of tissue. Selenium is necessary for converting the thyroid hormone T4 to its active form T3, aiding metabolism regulation. -
Immune Support:
Selenium enhances the body's immunity, supporting the production and efficacy of T-lymphocytes. -
Cancer Risk Reduction:
Epidemiological studies show that adequate selenium levels may reduce cancer risks by inducing apoptosis (programmed cell death) in abnormal cells. -
Reproductive Health:
Selenium supplementation can improve sperm motility and quality, aiding male fertility. Deficiency in selenium can lead to infertility due to oxidative damage to sperm cells. -
Heart Health:
Selenium's antioxidant properties help reduce oxidative stress linked to cardiovascular diseases. -
Neurological Protection:
Selenium contributes to the protection against Alzheimer's disease through its role in reducing oxidative damage in brain cells. -
Anti-inflammatory Effects:
Selenium influences inflammatory responses by modulating NF-kB pathways, reducing the production of inflammatory cytokines.
Dietary Sources of Selenium
- Tuna, cod, and seafood
- Poultry and meat (beef, chicken, lamb)
- Dairy products
- Cereals, rice, pasta
- Brazil nuts (exceptionally high in selenium)
- Eggs
The Recommended Daily Allowance (RDA) for selenium varies:
- Adults: 55–70 µg/day
- Pregnant women: 60 µg/day
- Lactating women: 60–75 µg/day
Caution: Selenium Deficiency & Toxicity
- Deficiency Risks: Can lead to Keshan disease (cardiomyopathy), infertility, weakened immunity, thyroid dysfunction, and increased oxidative stress.
- Toxicity Risks: Excessive selenium intake can cause nausea, vomiting, diarrhea, hair loss, and neurological damage.
References
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Kieliszek, M., Bano, I., & Zare, H. (2021). A Comprehensive Review on Selenium and Its Effects on Human Health and Distribution in Middle Eastern Countries. Biological Trace Element Research, 200:971–987. https://doi.org/10.1007/s12011-021-02716-z