Deliberations and evaluations of the approaches, endpoints and paradigms for selenium and iodine dietary recommendations

Abstract

Information is presented regarding the approaches that have been used to establish dietary recommendations for selenium and iodine. In the case of selenium, activity of the selenoenzyme glutathione peroxidase has served as a convenient biochemical endpoint for judging nutritional status. However, there are differences of opinion among various nutritionists as to whether full expression of this enzymatic activity is required for adequate nutriture, thereby resulting in differences in dietary recommendations. Endpoints for assessing selenium overexposure are much less satisfactory, but toxicological standards for selenium have nevertheless been established. Thus far, no nutritionists have attempted to shift the paradigm for determining dietary selenium recommendations away from prevention of deficiency disease to prevention of chronic degenerative disease (e.g., cancer). In the case of iodine, urinary excretion of the element is the most widely used endpoint for judging nutritional status. Numerous epidemiological surveys have been conducted to determine the level of urinary iodine excretion that is consistent with prevention of goiter, the most common endpoint of iodine deficiency. Because dietary iodine is essentially quantitatively excreted in the urine, determination of the latter in goitrous areas will allow an almost direct estimation of those intakes at risk of developing deficiency disease. Iodine toxicity is complicated by the fact that some persons are quite tolerant to the element whereas others are highly sensitive to it. There are relatively complete data sets concerning exposure vs. human health effects for both selenium and iodine so that sounder bases probably exist for their dietary recommendations than for many other trace elements.