Selenium in global food systems

Abstract

Food systems need to produce enough of the essential trace element Se to provide regular adult intakes of at least 40 m g/d to support the maximal expression of the Se enzymes, and perhaps as much as 300 m g/d to reduce risks of cancer. Deprivation of Se is associated with impairments in antioxidant protection, redox regulation and energy production as consequences of suboptimal expression of one or more of the Secontaining enzymes. These impairments may not cause deficiency signs in the classical sense, but instead contribute to health problems caused by physiological and environmental oxidative stresses and infections. At the same time, supranutritional intakes of Se, i.e. intakes greater than those required for selenocysteine enzyme expression, appear to reduce cancer risk. The lower, nutritional, level is greater than the typical intakes of many people in several parts of the world, and few populations have intakes approaching the latter, supranutritional, level. Accordingly, low Se status is likely to contribute to morbidity and mortality due to infectious as well as chronic diseases, and increasing Se intakes in all parts of the world can be expected to reduce cancer rates.

Selenium status in Southern Tasmania

“…It should also be noted that the maximum age for participation in the latter study was 65 years of age and there is some evidence of declining selenium levels in the elderly (Akbaraly et al, 2005). Plasma selenium levels are higher than those reported in many other countries, including New Zealand, but lower than reported levels in several countries including the USA and Japan (Combs, 2001). Interestingly, the proportion of participants less than 70 mg/l was 4/335 (1.2%) which is far less than the estimated prevalence (10-50%) of low selenium status (defined as less than 70 mg/l) by Combs (2001), based on reported blood selenium levels.…”

“…In the meantime, it would be reasonable to promote increased dietary intake of foods rich in selenium by individuals potentially most at risk of having suboptimal selenium levels, particularly young women, older men and those with low educational attainment. Two recent studies have shown associations between high selenium levels and fish and meat consumption in France and Britain (Arnaud et al, 2006;Bates et al, 2006), both countries with similar levels and estimates of depletion prevalence (10-50% o70 mg/l ) as Australia (Combs, 2001). …”

“…disease in humans relates to Keshan disease and Kashin-Beck disease (Combs, 2001). Given that anticarcinogenesis effects have been observed with mono-methylated forms of selenium (Ganther, 1999), only relying on selenoprotein saturation to determine threshold plasma selenium values for cancer prevention in humans may be an inappropriate approach.…”

“…Sulfur fertilization is also thought to interfere with selenium uptake by plants (Gupta & Gupta, 2002). As well as parts of China and Russia, central Africa, eastern Europe, New Zealand and regions of Scandinavia have been established as areas with low soil selenium and have demonstrated low levels in humans (Combs, 2001).…”

“…Selenium plasma levels for maximal glutathione peroxidase activity have been reported over the range 90-114 mg/l (Alfthan et al, 1991;Thomson et al, 1993;Duffield et al, 1999), whereas maximum selenoprotein P concentrations are reached around 83-118 mg/l (Marchaluk et al, 1995;Duffield et al, 1999), but may be as low as 71 mg/l in individuals with low selenium status (Hill et al, 1996). Rayman (1997) suggested a value of 100 mg/l as a threshold for nutritional adequacy although it has even been proposed that around 120 mg/l is a useful target for minimizing cancer risk (Combs, 2001). One significant limitation with plasma selenium threshold estimates, based on protein levels and activity, is that the positive health effects of selenium cannot be solely attributed to selenoproteins.…”