The impact of iodised salt or iodine supplements on iodine status during pregnancy, lactation and infancy.

OBJECTIVES: Monitoring of iodine status during pregnancy, lactation and infancy is difficult as there are no established reference criteria for urinary iodine concentration (UI) for these groups; so it is uncertain whether iodized salt programs meet the needs of these life stages. DESIGN AND SUBJECTS: The method used in this paper was: 1) to estimate the median UI concentration that reflects adequate iodine intake during these life stages; and 2) to use these estimates in a review of the literature to assess whether salt iodisation can control iodine deficiency in pregnant and lactating women, and their infants. RESULTS: For pregnancy, recommended mean daily iodine intakes of 220-250 microg were estimated to correspond to a median UI concentration of about 150 microg l- 1, and larger surveys from the iodine sufficient countries have reported a median UI in pregnant women > or = 140 microg l- 1. Iodine supplementation in pregnant women who are mild-to-moderately iodine deficient is beneficial, but there is no clear affect on maternal or newborn thyroid hormone levels. In countries where the iodine intake is sufficient, most mothers have median breast milk iodine concentration (BMIC) greater than the concentration (100-120 microg l- 1) required to meet an infant's needs. The median UI concentration during infancy that indicates optimal iodine nutrition is estimated to be > or = 100 microg l- 1. In iodine-sufficient countries, the median UI concentration in infants ranges from 90-170 microg l- 1, suggesting adequate iodine intake in infancy. CONCLUSIONS: These findings suggest pregnant and lactating women and their infants in countries with successful sustained iodised salt programs have adequate iodine status.