An evaluation of urinary measures of iodine and selenium status.

The aim of this study was to establish methodology for a survey of the iodine and selenium status of New Zealand residents, more specifically to investigate the correlation between fasting or random casual urine samples and 24 hour urines for iodine and selenium excretion. Sixty-two (31 M, 31 F) adults collected casual, fasting and 24 hour urine samples for analysis of iodide, selenium and creatinine. Plasma and serum samples were collected for analysis of selenium and glutathione peroxidase activity. Results indicated that fasting urine samples, but not casual urines, may give a reasonable estimate of urinary output of iodine and selenium on a population basis, but that 24 hour urines are necessary for diagnosis of iodine deficiency in an individual and for research purposes. The results for iodine also give no support for expressing iodine as the iodide-creatinine ratio, although there was some indication that the selenium-creatinine ratio might be useful. Significant correlations between total daily excretion of selenium and iodine and also for urinary concentrations of the two trace elements in fasting and in 24 hour urine specimens may reflect a relationship of selenium and iodine to body size which may have implications for dietary requirements of these trace elements. Alternatively the correlations may reflect a relationship between dietary intake of the two trace elements in a country in which food concentrations are low, and this needs further investigation.