J. Trace Elements Med. Biol. 14, pp. 210 - 217 April 2001 ~ourna} o Urinary selenium and and lactation iodine during © 2000 Urban & Fischer pregnancy C. D. Thomson 1, M. A. Packer*, J. A. Butler**, A. J. Duffield*, K. L. O'Donaghue*, P. D. Whanger** *Department of Human Nutrition, University of Otago, Dunedin **Department of Environmental and Molecular Toxicology, Oregon State University, Corvallis, Oregon, U.S.A. Summary Introduction The New Zealand environment is low in selenium and iodine, and is therefore ideally suited for the study of these anionic trace elements. The aim of this study was to determine urinary excre- tion of selenium and iodine during pregnancy and postpartum as part of an investigation of the influence of pregnancy and lacta- tion on selenium metabolism in women of low selenium status. In a double-blind placebo-controlled study, 35 women in the earliest stages of pregnancy and 17 non-pregnant women were recruited in Dunedin, New Zealand. Eighteen pregnant women received 50 gg selenium as L-selenomethionine, while the others received a placebo daily during pregnancy and 12 months postpartum. The non-pregnant women received the supplement, serving as a pos- itive control. Blood samples and twenty-four hour urine samples were collected monthly during pregnancy and at 3, 6, and 12 months postpartum for analysis of selenium and iodine. Selenium content in plasma and urinary excretion of selenium fell during pregnancy; however, total excretion of selenium was greater dur- ing pregnancy than postpartum. Urinary iodine excretion was much lower than reported previously in New Zealand. Due to large intra- and inter-subject variability, no trends in iodide excre- tion were observed. Factors which influence urinary excretion of selenium include dietary intake, but more closely, plasma con- centrations of selenium (which is probably related to total seleni- um pool), creatinine excretion and therefore lean body mass, and glomerular filtration rate. The exact mechanism and sequence of events remains unclear and future studies incorporating new speciation techniques are necessary. Keywords: Selenium, iodine, urinary excretion, preg- nancy, postpartum (Received June/October 1999) Reprint requests to: Prof. C. D. Thomson, Department of Human Nutrition, University of Otago, PO Box 56, Dunedin, New Zealand The New Zealand environment is low in selenium, iodine and fluorine, and is therefore ideally suited for the study of these anionic trace elements. The low selenium status of New Zea- land residents has been well documented (1, 2). Low selenium and glutathione peroxidase (GSHPx) activity during pregnancy may compromise the antioxidant status of newborn babies, es- pecially already vulnerable premature infants (3, 4). New Zea- land also has a history of iodine deficiency prior to the introduc- tion of iodisation of table salt in 1939, after which goitre was virtually eliminated (5). From the 1960s iodine intake increased further through contamination of dairy products with the use of iodophor cleaning agents in the dairy industry. However, with the reduction in the use of these compounds, and the dietary rec- ommendation to reduce our salt intake, the iodine intakes of New Zealanders appear to be falling. Urinary iodide excretions in recent years (6, 71 were considerably lower than values previ- ously reported for New Zealand (8, 9), Adequate iodine status during pregnancy is critical for the protection of the fetus against retarded mental development associated with iodine de- ficiency disorders (10, 11). Selenium has an important role in thyroid hormone metabo- lism as an active component of Type I and possibly also Type II 5' iodothyronine deiodinase (12, 13), and the interaction of sele- nium and iodine during pregnancy and the perinatal period may influence development of iodine deficiency disorders in infants (14). Therefore the interrelationship between selenium and io- dine nutrition is of special interest in New Zealand where the status of both trace elements is low. Continual surveillance of the iodine and selenium status of the population is necessary to monitor effects of changes in dietary habits, availability of food products and agricultural practices (15). The initial aim of this