Iodine deficiency in Australian and New Zealand infants

Two recently published studies have confirmed the low iodine status of Australian and New Zealand ( NZ) infants. Both studies were undertaken between 2001-2006 prior to the National Health and Medical Reseach Council's (NHMRC) recommendation that pregnant and lactating women take a daily iodine supplement of 150ug and the mandatory iodine fortification of bread.

Iodine is an essential nutrient. Deficiency in infants can result in brain damage, mental retardation, growth stunting and impaired hearing, speech and learning. Iodine contents of foods relect the soil iodine content and in many parts of Australia and New Zealand the soil in low in iodine. The iodine content of breast milk reflects the iodine content of mothers diet.

The NZ study carried out in 2004/5 looked at the iodine status of breast feeding mothers and their infants during the first 6 months postpartum. Mothers were divided into 3 groups - one group received a 75ug daily iodine supplement, one a 150ug daily iodine supplement and the other no supplemental iodine. Iodine status of both mothers and infants was measured at 1,2,4,8,12,16 and 24 weeks postpartum using urinary iodine excretion (UIE). The breast milk iodine concentration (BMIC) at these times was also measured. Mothers finished their pregnancy mildly iodine deficient as indicated by UIE. During the 24 weeks of breast feeding both supplemented and unsupplemented mothers remained iodine deficient, the supplemented mothers being less iodine deficient than the unsupplemented. BMIC was higher in the supplemented goups, being at least 40% lower in the unsupplemented group. However, supplementation with either 75ug or 150ug of iodine daily didn't raise BMIC high enough to increase their infants UIE to adequate levels. Thus the low BMIC of breast milk was reflected in the infants UIE. Despite mild iodine deficiency the infants appeared physically well. Low iodine levels for mothers may reflect in tiredness or depression. The study throws doubt as to whether a 150ug daily supplement of iodine as recommended by the NHMRC will be sufficient to raise iodine in breast feeding mums and their infants in low iodine countries like NZ and Australia to sufficent levels.

The Australian study looked at the iodine status of Victorian infants born between 2001-2006. Heel prick blood samples,  routinely taken 2-4 days after birth as part of neonatal screening tests were analysed for Thyroid Stimulating Hormone  (TSH) concentration in over 368,000 infants born during this period. Using this as a measure of iodine deficiency, the study found an increasing incidence of iodine deficiency over this time - 4% in 200l vs 9.65% in 2006. Infants from metropolitan areas had a higher incidence of iodine deficiency than those from rural areas.  The National Iodine Nutrition Survey of school children also found mild iodine deficiency aroung this time.

These studies highlight the importance of ensuring women ( pregnant and breastfeeding ) and their infants receive sufficient iodine in their diet. They will also provide important baseline data when evaluating the new recommendations on iodine supplementation and iodine fortification of bread.

References

Mulrine HM, Skeaff SA et al. Breast milk iodine concentration declines over the first 6 months postpartum in iodine deficient women. Am J Clin Nutr 2010;92:849-856

Rahmna A, Savige GS et al. Increased iodine deficiency in Victoria, Australia: analysis of  neonatal thyroid stimulating hormone data, 2001-2006. MJA 2010;193(9):503-505