Selenium and Iodine for Thyroid Health

  1. Selenium and Iodine for Thyroid Health

    Mostly about selenium. Will add more iodine info as it turns up on PubMed.

    1: Hell J Nucl Med. 2006 Sep-Dec;9(3):195-203.Links
    [Selenium and thyroidal function; the role of immunoassays]
    [Article in Greek, Modern]

    Kaprara A, Krassas GE.

    Department of Endocrinology, Diabetes and Metabolism, Panagia General Hospital, N Plastora 22, 551 32 Kalamaria, Thessaloniki, Macedonia, Greece.

    It is well known that selenium plays a fundamental role in regulating thyroid and other functions of the human body like reproduction, autoimmunity, glucose metabolism or bone metabolism. While for thyroid function investigation, radioimmunoassays and radioimmunometric assays both key techniques of nuclear medicine are used, for selenium measurements atomic absorption spectrometry is the method of choice. Normal thyroid gland retains high selenium concentrations even under conditions of inadequate selenium supply and expresses many of the known selenocysteine-containing proteins. Adequate selenium nutrition supports efficient thyroid hormone synthesis and metabolism and protects the thyroid gland damage by excessive iodide exposure. In regions where a combined severe iodine and selenium deficiency exist, normalization of iodine supply is mandatory before initiation of selenium supplementation in order to prevent hypothyroidism. Selenium deficiency and disturbed thyroid function may develop under conditions of special dietary regimens, such as long-term total parenteral nutrition or after inadequate nutrition in children. Some investigators suggest that selenium may be a useful adjunctive treatment for autoimmune thyroid diseases, such as Hashimoto and Graves' disease. Low serum selenium levels have been associated with higher incidence of thyroid cancer, as well as with chronic illness or lomicronw triiodothyronine syndrome. These biological actions are mediated through the expression of selenoproteins, the most important being the glutathione peroxidases, the iodothyronine deiodinases, the thioredoxine reductase and the selenoprotein P. Selenium is also associated with animal proteins. Subsequently meats and seafood are dietary sources of selenium. The ingestion of large quantities of selenium may have adverse effects. It has been shown that dietary intake of about 300 micro g of selenium daily may have a toxic effect on growth hormone and insulin like growth factor-1 metabolism, as well as in the synthesis of thyroid hormones. Main adverse effects may be anorexia, diarrhea, depression, hemorrhage, liver and kidney necrosis, blindness, ataxia and respiratory disturbances. Dermatitis and CNS deficiency have also been described. It is concluded that selenium plays an important role in regulating thyroid function, as well as in the homeostasis of thyroid hormones through the action of selenoproteins, in which it incorporates as selenocystein.

    PMID: 17160166 [PubMed - indexed for MEDLINE]

  2. Iodine uptake and loss-can frequent strenuous exercise induce iodine deficiency?
    Smyth PP, Duntas LH.

    Endocrine Laboratory, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Ireland. [email protected]

    Most of the daily dietary iodine intake (approximately 90 %) will be excreted in the urine; measurement of urinary iodine excretion is thus routinely used as an index of dietary iodine intake. However, urinary excretion is not the only means of iodine loss. Subjects such as athletes or those participating in vigorous exercise can lose a considerable amount of iodine in sweat, depending on environmental factors such as temperature and humidity. In areas of lower to moderate dietary iodine intake, loss in sweat can equal that in urine. Although electrolyte loss in sweat is well-recognized and replacement strategies are adopted, there is less recognition of potential iodine loss. Crude calculations reveal that if sweat iodide losses are not replaced, dietary stores could be depleted in an athlete undergoing a regular training regime. The significance of these losses could be increased in areas where dietary iodine intake is lower in the summer months. Although there is little doubt that excessive sweating can induce a relative iodine deficiency state, there is no case as yet for iodine supplementation in those that take vigorous exercise. However, sustained iodine loss may have implications for thyroid status and possibly consequences for athletic performance.

    PMID: 16175493 [PubMed - indexed for MEDLINE]

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