Abstract
Leo Sher, Riverdale, New York:
The element selenium, named after the Greek goddess of the moon Selen, was discovered by the Swedish scientist Berzelius in 1817 [1]. Selenium is an essential nutrient of fundamental importance to human biology [1, 2]. There is evidence that decreased selenium status can have adverse consequences for the maintenance of optimal health [1, 2]. Low selenium status can be a result of low selenium intake. Levels of selenium in blood and tissue can also be affected in patients with chronic renal failure treated by haemodialysis or by chronic peritoneal dialysis [3].
Selenium is an antioxidant and catalyst and is required for appropriate thyroid hormone synthesis, activation, and metabolism [1, 2]. The human thyroid gland has the highest selenium content per gram of tissue among all organs. Several selenocysteine-containing enzymes are functionally expressed in the thyroid: three forms of glutathione peroxidases, the type I 5-deiodinase, thioredoxin reductase and selenoprotein P. Low selenium status may compromise thyroid-hormone metabolism. The findings of an essential role of selenium for thyroid hormone synthesis and metabolism raise the question whether if in addition to iodine supplementation we also need selenium supplementation to optimize the function of thyroid axis.
Both hypo- and hyperthyroidism may be associated with changes in mood, behaviour, and cognitive function [1, 4]. Considerable evidence has accrued within the last several decades suggesting that the boundary between normal thyroid function and thyroid dysfunction is not distinct. There is evidence that small changes in thyroid function might be biologically meaningful and affect mood and behaviour [4].
Multiple lines of evidence suggest that selenium deprivation leads to depressed mood, and high dietary or supplementary selenium seems to improve mood [1, 2]. Several researchers reported that low selenium status was associated with a significantly increased incidence of depression, anxiety, confusion, and hostility. Low plasma selenium concentrations in the elderly were significantly associated with senility and cognitive decline [1, 2]. Brain selenium level in Alzheimer's patients is only 60% of that in controls. The effect of selenium status on mood, behaviour, and cognition may therefore be partly mediated by changes induced by selenium deficiency or selenium supplementation in thyroid function [1, 5].
Selenium deficiency decreases immunocompetence and promotes viral infections [2]. It has been suggested that viruses may be capable of using the selenium supply of the host by incorporating selenium into viral selenoproteins, thereby reducing the ability of the host to produce an effective immune response. Patients who have a combination of depression, hypothyroidism, and increased susceptibility to viral infections should therefore be assessed for selenium deficiency, especially if they live in an area where the soil is low in selenium [1, 5].