Functional indicators of iodine and selenium status

The micronutrient I, which has only one known biological function as a comp onent of thyroid hormones, contrasts with Se, which is essential for many b iochemical pathways through a range of Se-containing proteins. Thus, for I it is less complicated to propose and validate biochemical or functional ma rkers which represent the adequacy or otherwise of dietary intake than it i s to perform the same task for Se. Plasma thyroid-stimulating hormone provi des a good indicator of functional I status, since levels of the hormone in crease to compensate for any inadequacy in available dietary I. This increa se occurs even when problems are caused by goitrogens restricting utilizati on of dietary I that otherwise would be adequate. In contrast, there are ma ny potential indicators of Se status, especially since the many Se-containi ng proteins relate to different biochemical functions in the body. However, determination of the different GSH peroxidase (EC 1.11.1.9) activities in blood or tissue may give a useful indication of 'functional Se status', sin ce these selenoproteins are often the most sensitive indicators of dietary Se intake. This approach has been successful in many experiments where anim als of a similar genetic background have consumed diets which differ only i n their Se content. Unfortunately, use of indicators of Se status in human populations may be complicated by differences (possibly genetic) between in dividuals that increase variability of selenoenzyme activities. The most ap propriate indicator of functional Se status may also vary with other dietar y conditions such as vitamin E or I deficiencies which may interact with Se deficiency. However, taking particular circumstances into account, determi nation of blood or tissue selenoprotein activity can provide a useful marke r of adequacy of dietary Se supply for maintaining optimal health.