Selenium is an important trace mineral required for the correct function of the glutathione peroxidase enzyme. The role of glutathione peroxidase as a cellular antioxidant highlights the importance of selenium in the prevention of disease such as cancer and cardiovascular disease, both of which may have an aetiology involving free radical damage. The best source of minerals is usually from the diet as plants tend to store them in absorbable forms that are superior in efficacy when compared to most dietary supplements. However, low selenium soils have been recognised as a problem for many decades because they can produce crops that are deficient in selenium and this can cause deficiency diseases in any population relying on that crop as a source of nutrition. In addition, the shift from traditional diets to the Western diet has caused a reduction in the intakes of dietary selenium, due mainly to the refining of grains, and this in turn has lead to the selenium status of many developed nations being highlighted as insufficient for optimal health.
Biochemical individuality makes it difficult to make recommendation on selenium intakes because the range of intakes required in a population can be diverse. Although the recommended levels are usually suitable for most people, some will always require more of a particular micronutrient than others. In this regard metabolic studies have attempted to assess the intakes of minerals such as selenium that are required to keep individuals in a positive balance, and therefore free of disease. For example, in one study1 researchers measured the dietary selenium required for a positive selenium balance in healthy adults using 4 one week periods over the course of 12 months. The results showed that men had higher selenium intakes than women (90 μg versus 74 μg, and this was likely a reflection of the higher calorie intake of the men. There was little plasma variation in selenium over the course of different seasons. Analysis of the intakes and selenium balance of the subject showed that men required 80 μg per day, whereas women needed only 57 μg per day.
Adjustment of these figures for body weight in men and women showed a rough estimate of 1 μg of dietary selenium per kg bodyweight per day to maintain balance. The question that arises from this study is whether the diet can supply adequate amounts of selenium to meet these needs. Based on the fact that selenium deficiencies are rare it must be said that the typical Western diet can supply enough selenium to prevent outright selenium deficiency. However, there is a large body of evidence that suggests that while deficiencies of selenium are uncommon, insufficiencies of selenium are highly prevalent within developed nations. Eating a traditional diet containing foods grown on high selenium soils would likely supply the required selenium intake. However, even then selenium intake cannot be guaranteed to be consistent and in countries such as New Zealand where selenium deficient soils are present dietary intakes are unlikely to supply enough selenium without relying on nutritional supplements.
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