Selenium, zinc and copper status in Tasmania: dietary, lifestyle and some genetic associations

Micronutrient deficiency is a public health problem thought to affect a third of the world's population. In Tasmania, selenium deficiency occurred in livestock, and it has been hypothesised that the human population may be at risk of inadequate intakes. There are few Australian studies of trace element status, and previous studies in Tasmania have been very limited and have provided conflicting results. The primary aim of this thesis was: To assess the selenium status of people in northern Tasmania; To identify factors that may influence selenium status in these people; To determine groups in this population that may be at increased risk of low selenium status. A secondary aim was to conduct an opportunistic study to assess the copper and zinc status in the same population, and determine some of the factors which may be associated with copper and zinc status in this population. The main study was a cross sectional population study of approximately 500 subjects randomly selected from the electoral roll in the northern Tasmania; this was preceded by a preliminary study which used a convenience sample from this same geographical region, and some technical work on the assessment of copper and zinc status. Indices of trace element status measured included dietary intake, serum levels and functional markers of status, such as glutathione peroxidase activity for selenium status. This was linked with data on lifestyle habits, anthropometric measurements, dietary analysis for other nutrients, and the measurement of total antioxidant status and lipid profiles. Results from the preliminary research (n = 198) suggested that marginal selenium status may be reasonably widespread in this population, and that certain gender/age groups may also consume inadequate zinc. Hereditary haemochromatosis was not observed to have a major effect on trace element status. The population study on 498 subjects from the electoral rolls of north, north west and north eastern Tasmania, suggested a high prevalence of marginal selenium status. Northern Tasmanians had mean selenium intakes of 77.4 and 65.1 ìg/d for men and women respectively; with 27% of all subjects consuming inadequate amounts of selenium as indicated by NH&MRC guidelines on dietary intakes. Mean serum selenium was 1.13 ìmol/L; and hence a large proportion of the population (80%) was estimated to have serum selenium concentrations below threshold levels associated with selenoprotein requirements. The majority of subjects also had serum selenium concentrations below the level suggested to offer chemopreventative benefits for some cancers. Associations with a common selenoprotein SNP were not found. In investigations of zinc status, men in particular appeared at risk of inadequacy. Zinc intakes were 12.6 and 10.9 mg/d for men and women respectively. Fifty two percent of men consumed inadequate zinc compared to only 9% of women. Mean serum zinc concentration was 13.0 ìmol/L and when compared to the WHO cut-off, 15% of all men had low serum zinc; the prevalence of which rose in older age ranges. Investigations of copper status suggested that copper deficiency was unlikely in this population. Mean serum copper concentrations were 15.5 and 18.9 ìmol/L for men and women respectively; well above the lower clinical reference range. These findings indicate that many Tasmanians may have marginal selenium status, and that particular population sub-groups may additionally be susceptible to inadequate zinc status. Further research is required. However, with our increasing understanding of the importance of these essential trace elements in maintaining health and for reducing susceptibility to some chronic diseases, the findings are important. There is potential, to be tested, that increased intakes could possibly benefit an aging Tasmanian population, which leads the country in chronic disease rates.