Jean-Baptiste Vanderpas

Effect of selenium supplementation on thyroid hormone metabolism in an iodine and selenium deficient population

OBJECTIVE Severe selenlum deficiency has been documented In northern Zaïre, already known as one of the most Iodine deficient regions In the world and characterized by a predominance of the myxoedematous form of cretinism. This has been attributed to the double deficiency of essential trace elements. A short selenium supplementation programme was conducted In this area to evaluate the effects of a selenium supplementation on thyroid diseases.

Cretinism, thyroid hormones and selenium

The effect of angiotensin II on cytosolic free Ca 2+ ion concentrations ([Ca 2+ ] i ) were studied in single porcine granulosa cells using the calcium-sensitive fluorescent dye fura-2 and high temporal resolution fluorescent videomicroscopy. Angiotensin II initiated specific, rapid, transient and topographically organized increases in [Ca 2+ ] i in a subpopulation of single swine granulosa cells

Selenium status in pregnant women of a rural population (Zaire) in relationship to iodine deficiency.

Endemic myxoedematous cretinism has been associated with combined selenium and iodine deficiency in several areas of Zaire. To determine selenium and iodine status across the country, serum selenium and thyroid function parameters including urinary iodide were determined at prenatal clinics in 30 health centres of rural villages distributed over the whole country. Only in Bas‐Zaire was the mean serum selenium level similar to that in non‐deficient areas (80–120 ng/ml); in the regions of Bandundu and Kasai levels were marginally decreased (55–80 ng/ml), and in Kivu, Haut‐Zaire, Equateur and Shaba they were marginally or moderately decreased (<55 ng/ml). The frequency of abnormally low urinary iodide (<5 μg/dl) varied from 20% in the region of Bas‐Zaire to 50% in Kasai (P<0.001), and to still higher percentages in the 5 other regions of Zaire (Bandundu, 57%; Kivu, 63%; Equateur, 72%; Shaba, 76%; Haut‐Zaire, 84%). With the exception of Bas‐Zaire, biochemical maternal hypothyroidism (serum TSH >5mU/l) was present in every region, with a frequency ranging from 3% in Kivu to 12% in Equateur. Iodine deficiency affects most of the Zairean population and requires public health measures on a larger scale than previously estimated. Combined iodine and selenium deficiency affects Equateur, Haut‐Zaire and Kivu, where endemic myxoedematous cretinism occurs, but also Shaba, where it was not previously described. Besides combined iodine and selenium deficiency which is permissive, another factor (thiocyanate?) must be taken into account to explain the peculiarly elevated prevalence of endemic myxoedematous cretinism in Central Africa.

Historical aspects of iodine deficiency control

In 1895, iodine was characterized as an essential element of thyroid tissue by Baumann. The efficacy of iodine to prevent goiter was demonstrated by Marine in Northern USA in 1916-1920. Severe endemic goiter and cretinism had been almost entirely eliminated from continental Western Europe and Northern America before the 1930s; however large populations elsewhere and even some places in Western Europe (Sicily) were still affected up to the 2000s. Public health consequences of iodine deficiency are not limited to endemic goiter and cretinism. Iodine deficiency disorders include also increased neonatal death rate and decreased intellectual development, although these consequences are not included in the current estimation of the Global Burden Disease related to iodine deficiency. Severe iodine deficiency as a public health problem is now largely under control worldwide, but can still affect isolated places, in hard-to-reach and/or politically neglected populations. We emphasize the importance of maintaining international cooperation efforts, in order to monitor iodine status where iodine deficiency is now adequately controlled, and identify at-risk population where it is not. The goal should be now global eradication of severe iodine deficiency. Commercial distribution of iodized salt remains the most appropriate strategy. A randomized clinical trial in New Guinea clearly showed in the 1970s that correcting severe iodine deficiency early in pregnancy prevents endemic neurological cretinism. This supports the essential role of thyroid hormones of maternal origin on the normal fetal development, during the first trimester of pregnancy (i.e. when fetal thyroid is still not functional). A randomized clinical trial in Congo (RD) in the 1970s also showed that correcting severe iodine deficiency during pregnancy prevents myxœdematous cretinism, particularly prevalent in affected Congolese areas.