Selenium Interventions

As noted previously, neither Keshan disease nor Kashin-Beck disease are now thought to be simple dietary deficiency diseases. They probably also involve viral components and may be exacerbated by environmental toxins, including mycotoxins. Thus, they are probably multifactorial, but importantly, public health selenium supplementation interventions have had a dramatically beneficial effect on the prevalence of these diseases. The main clinical features of Keshan disease are cardiac insufficiency and enlargement, electrocardiographic changes, and fibrosis. Those of Kashin-Beck disease are osteoarthropathy and necrosis of the joints and epiphysial plate cartilage. Both diseases occur in school-age children; Keshan disease also occurs in women of child-bearing age, but adult men are less affected.

In hilly and heavily eroded areas of China where these diseases were endemic, the use of selenium-enriched fertilizers was not feasible as an intervention because of the huge geographical areas involved and hence the high cost. Instead, direct human supplementation of at-risk and affected populations was introduced during the 1970s using a 0.5 or 1.0 mg sodium selenite supplement (according to age) per person per week. In Shaanxi province, following supplementation, the prevalence of Keshan disease declined from 12 per 1000 to undetectable levels between 1976 and 1985, and in Heilongjiang province the prevalence of Kashin-Beck disease declined from 44 to 1% of the population between 1970 and 1986.

An alternative approach to intervention, by selenium enrichment of crop and grassland fertilizers, was introduced in the 1970s in Finland. Here, there was no overt evidence of selenium deficiency in the human population, but Se deficiency disease had occurred, and had been successfully eliminated in farm animals, by supplementation of animal feeds during the 1960s. Fertilizer that was Se enriched at 16mg/kg was then applied to cereal crops for human consumption. Grassland fertilizer was enriched at 6mg/kg. As a result, adult human Se intake increased from 25-60 to approximately 100 mg/day. Serum Se increased from 65-70 mg/l in

1975 to 120 mg/l in 1989-1991. In 1990, the selenium level was reduced to 6 mg/kg fertilizer for cereal crops as a precaution against possible overload. Selenium intervention by fertilizer enrichment was judged to be a safe, economical, and easily controlled intervention.

New Zealand, which has a similar situation of marginal intakes and status, decided not to intervene on a population or nationwide basis but instead has taken steps to ensure that particular high-risk groups, notably people receiving total parenteral nutrition or children receiving special diets for phe-nylketonuria prevention, are adequately supplied.

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