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'Narrow' range for ideal iodine intake in weaning infants
In comparison to other age groups, the association between urinary iodine concentration and thyroglobulin in infants aged 6 to 24 months forms a similar U-shape, but the range for optimal iodine intake is narrower, according to findings published in Thyroid.
“Pediatric guidelines recommend no extra salt be given to infants during the first year and that cow’s milk should not be introduced as a drink before the age of 12 months. The dietary sources of iodine for this age group may, thus, be limited,” Jessica Farebrother, MPharm, MPH, from the department of human nutrition at the Institute of Food, Nutrition and Health in Zurich, and colleagues wrote. “Our group has previously shown that weaning infants are at risk of iodine deficiency and may be vulnerable to thyroid dysfunction with chronic excess iodine intakes.”
Farebrother and colleagues conducted a cross-sectional study with 1,543 weaning infants aged 6 to 24 months (mean age, 12.2 months) who consumed breast milk and complementary foods. Participants were from 12 sites in seven countries, including Morocco, the Gambia, the Philippines, China, Croatia, Tanzania and Kenya.
Food intake patterns and content as well as exposure to iodine, iodized salt and foods that contained iodine were assed via questionnaires answered by each infant’s parent or guardian. The researchers determined iodine status by collecting spot urine samples and measured thyroglobulin, thyroid-stimulating hormone and total thyroxine via dried blood spot samples.
Among the different countries, median urinary iodine concentration varied between 48 µg/L and 552 µg/L while estimated iodine intake fell between 21 µg per day and 233 µg per day. The researchers noted that iodine was provided mainly via breast milk. Thyroglobulin levels peaked at sites with the lowest and highest urinary iodine concentrations (P < .001), which the researchers said was indicative of a U-shaped pattern. There was a correlation between urinary iodine concentration and TSH (P < .01) and T4 (P < .05) for the entire population, but not on a site-by-site basis. In addition, the researchers noted a negative correlation between thyroglobulin and age (P = .018).
In the study population, very few thyroid disorders were reported. Subclinical hyperthyroidism was the most common, particularly in Morocco (P < .05).
“We observed the same U-shaped association between [urinary iodine concentration] and [thyroglobulin] concentrations as documented in other population groups. However, in this age group compared to older children and adults, the optimal iodine intake range appears narrow,” the researchers wrote. “Though our study was not designed to define the optimal iodine intake, the data presented suggest that the median [urinary iodine concentration] threshold of 100 µg/L defining adequate iodine nutrition in this group may be too low. ... The results suggest that the median [urinary iodine concentration] range reflecting optimal iodine nutrition in young infants may be higher than for older children.” – by Phil Neuffer
Disclosures: The authors report no relevant financial disclosures.