Keshan disease is an endemic cardiomyopathy of unknown cause in The People's Republic of China that occurs most frequently in children under 15 years of age and women of child-bearing age. Studies of children 1-9 years old in Mianing County of Sichuan Province have indicated that Keshan disease is a selenium responsive condition. Incidence rates of 9.5-13.5/1000 in 1974-1975 were reduced to 1-2/1000 in children treated with a tablet weekly of 0.5-1 mg sodium selenite. During 1974-1977, only 21 cases of the disease occurred in 36,603 treated children, compared with 106 cases in 9430 untreated children, of whom 53 died and 5 still have insufficient heart function. Occurrence of the disease was invariably associated with a lower selenium content of cereals, and of hair (less than 0.12 ppm Se) in residents from affected, compared with non-affected, areas. The dose relationship between selenium and regional characteristics of Keshan disease suggests that it is probably a biogeochemical disease; other etiological factors have also been considered.

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A study was undertaken in eight healthy young men to examine the effects of varying intakes of threonine on plasma free threonine concentrations and threonine kinetics, using a 3 h constant intravenous infusion of L-[1-13C]threonine. Subjects consumed diets based on an L-amino acid mixture, in which the quality of threonine was reduced every 7 days. On the last day of each diet period, determinations of plasma threonine flux and threonine oxidation were carried out while subjects consumed small meals, each supplying 1/12 daily intake, at hourly intervals. Threonine oxidation rates fell with reduced threonine intake, reaching a relatively constant level at intakes of 20 mg.kg-1.day-1 and below. These metabolic data are discussed in relation to the currently established value of 7 mg.kg-1.day-1 as the upper range of the threonine requirement for healthy young adults. It is concluded that actual threonine requirements may be considerably higher for this age group.

Healthy young men participated in a study designed to explore the effects of decreasing dietary lysine content on plasma amino acid concentrations and lysine kinetics, studied with L-[1-13C]lysine as tracer. Diets provided adequate energy and the equivalent (N X 6.25) of 0.8 g protein kg-1.day-1 as a synthetic L-amino acid mixture simulating egg protein. Lysine intake was reduced every 7 days. Changes in plasma amino acids suggested that effects characteristic of a dietary lysine inadequacy were prevented by consuming more than 32 mg lysine.kg-1 day-1. Primed, continuous intravenous infusions of L-[1-13C]lysine, at the end of each diet period while subjects were in the fed state, showed that as dietary lysine was reduced, 13C enrichment increased in plasma lysine and decreased in expired CO2. It was estimated that lysine oxidation exceeded, by 4.4 mg kg-1 day-1, the lysine intake of 20 mg kg-1.day-1 indicating that the lysine required for body protein maintenance would probably exceed this latter value. These results are discussed in relation to the physiological requirement in adults for lysine, currently accepted to be met by an intake of 12 mg kg-1.day-1. which is assumed to be the upper range of the lysine requirement for this population group.