min E, and selenium for each life-stage group above age 12 months. In each case, criteria were based on a specific function and not on the prevention of chronic disease. The report also addresses beta-carotene and the carotenoids; but no EARs, RDAs, or ULs were established for any of those substances.
Considerable research has been conducted on selenium in the past 6 years. In basic science, for example, 25 genes have been identified that code for selenoproteins. Characterization of these genes is now in progress and is expected to yield useful functional information and clarification of biochemical mechanisms.
Selenoprotein P is now considered a highly promising biomarker for selenium status. It could be considered along with selenium-dependent glutathione peroxidase (the current functional indicator) by a future DRI panel.
Disease prevention was and continues to be a particular area of interest related to the antioxidant nutrients. The ongoing Selenium and Vitamin E Chemoprevention Trial (SELECT), a very large cancer prevention clinical trial involving 35,000 men, will provide much needed clinical data on possible roles of selenium in disease prevention and on adverse effects that may occur with selenium supplementation. The basis for SELECT comes from the Selenium Skin Cancer Prevention Trial (Clark et al., 1996), which studied skin cancer prevention resulting from 4.5 years of supplementation with 200 µg/day of selenium in the form of selenium-enriched yeast. No reduction in second skin cancers occurred; but, unexpectedly, fewer cancers of the prostate, lung, and colorectum were noted in the group that received selenium supplements. The SELECT trial is designed to try to replicate this provocative finding. Figure 5-1 depicts the SELECT study design.