Selenium Deficiency...continued.

Reference from the joint report of FAO/WHO expert consultation on Human Vitamin and Minerals verbatim.

Selenium and thyroid hormones

35. Arthur, J.R., Nicol, F. & Beckett, G.J. 1993. Selenium deficiency thyroid hormone metabolism and thyroid hormone deiodinases. Am. J. Clin. Nutr., Supplement, 57:

236S-239S.

36. Corrilain, B., Contempre, B., Longombe, A.O., Goyens, P., Gervy-Decoster, C., Lamy, F., Vanderpas, J.B. & Dumont, J.E. 1993. Selenium and the thyroid: how the relationship was established. Am. J. Clin. Nutr., Supplement 57: 244S-248S.

The importance of selenium for thyroid hormone metabolism (35, 36) is evident from changes in the T3-T4 ratio which develop after relatively mild selenium depletion in infants and elderly (65+ years) subjects.

37. Olivieri, O., Girelli, D., Stanzial, A.M., Rossi, L., Bassi, A. & Corrocher, R. 1996. Selenium, zinc and thyroid hormones in healthy subjects. Low T3/T4 ratio in the elderly is related to impaired selenium status. Biol. Trace Elem. Res., 51: 31-41.

38. MacPherson, A., Barclay, M.N.J., Scotts, R. & Yates, R.W.S. 1997. Loss of Canadian wheat imports lowers selenium intake and status of the Scottish population. In: Trace Elements in Man and Animals -Proceedings of 9th International Symposium on Trace

Elements in Man and Animals. Fischer, P.W.F., L'Abbe, M.R., Cockell, K.A., Gibson, R.S. p. 203-205. eds. Ottawa, Canada, NRC Research Press.

39. Vanderpas, J.B., Contempre, B., Duale, N.L. & Deckx, H. 1993. Selenium deficiency mitigates hypothyroxinimia in iodine deficient subjects. Am. J. Clin. Nutr., 57 Suppl: 271S-275S.

Decreases in the T3-T4 ratio indicative of decreased thyroid hormone balance have been detected when serum selenium falls below 0.9 μmol/l (37). In a recent Scottish study these decreases were correlated with a decline in dietary and plasma selenium after the replacement of selenium-rich wheat from Canada and the United States with selenium-deficient wheat from European sources (38). Communities noted for a high incidence of myxedematous cretinism have been found to have low plasma selenium status and GSHPx activity in addition to having low iodine status (39) and being exposed to high thiocyanate intakes from cassava.

40. Contempre, B., Le Moine, O., Dumont, J.E., Denef, J-F. & Many, M.C. 1996. Selenium deficiency and thyroid fibrosis. A key role for macrophages and TGF-á. Mol. Cell. Enyzmol., 124: 7-15. 

Restoration of iodine supply, particularly if excessive, tends to induce a high peroxidative stress through the action of iodide peroxidase, the first step in iodine utilisation by the thyroid. It is postulated that necrosis and thyroid fibrosis leading to irreversible hypothyroidism result if a concurrent deficiency of selenium limits peroxide destruction by the protective action of the seleniumdependent enzymes, GSHPx and, more probably, thioredoxin reductase (40).

39. Vanderpas, J.B., Contempre, B., Duale, N.L. & Deckx, H. 1993. Selenium deficiency mitigates hypothyroxinimia in iodine deficient subjects. Am. J. Clin. Nutr., 57 Suppl: 271S-275S. 

41. Ma, T., Guo, J. & Wang, F. 1993. The epidemiology of iodine deficiency diseases in

China. Am. J. Clin. Nutr., Supplement, 57: 264S-266S.

42. Contempre, B., Many, M.C., Duale, G.L., Denef, J.F. & Dumont, J.E. 1996. Selenium and iodine in thyroid function: the combined deficiency in the etiology of the involution of the thyroid leading to myxoedematous cretinism. In: Thyroid and Trace Elments. 6th Thyroid Symposium. p. 35-39. Eds. Browerman, L.E., Kohsle, J., Eber, O., Langsteger, W. Graj-Eggenberg: Barmhersige Brudes.

In areas where myxedematous cretinism is endemic and characterised by persistent hypothyroidism, dwarfism, and stunting, it has been recommended that attempts to introduce iodine therapy for mildly affected individuals should be preceded by an assessment of selenium status and rectification of any observed deficit (39). Although this suggestion is compatible with pathologic observations on hypothyroid rats differing in selenium status, its validity has yet to be assessed adequately in humans (41, 42).