Describe Selenium under the headings of 'its dietary sources', 'its biochemical roles' and 'its deficiency diseases' with their clinical manifestations.
Selenium is an essential trace element required for diverse physiological functions. Dietary sources include Brazil nuts, seafood such as tuna and cod, organ meats, poultry, eggs, and whole grains. Its content in plant foods varies with soil selenium concentration.
Biochemically, selenium is incorporated into selenoproteins as selenocysteine, the 21st amino acid. These proteins act as antioxidants (e.g., glutathione peroxidase), regulate thyroid hormone metabolism via iodothyronine deiodinases, and contribute to immune function, DNA synthesis, and reproductive health. By limiting oxidative stress, selenium safeguards cellular integrity.
Deficiency diseases include Keshan disease, a cardiomyopathy affecting children and young women, and Kashin-Beck disease, an osteoarthropathy causing joint deformity and growth retardation. Myxedematous endemic cretinism arises when selenium deficiency coexists with iodine deficiency, producing hypothyroidism and neurological deficits.
Clinical manifestations range from fatigue, muscle weakness, hair loss, and nail dystrophy to impaired immunity, heart failure, and neurological dysfunction in severe deficiency.
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