Iodine Deficiency, Goiter and Nutritional Status Assessment
Last week at the American Society for Nutrition annual meeting, DSM scientists reported ~ 25% of American adolescents and adults were clinically deficient in at least one micronutrient. For more details read Hidden Hunger: Micronutrient Deficiencies are prevalent among US adolescents and Think Nutrient Deficiencies are History in the US? Think Again.
Iodine was the nutrient most often found to be deficient. Why is that? Iodine intake reflects the iodine content of soil because that dictates the amount absorbed by plants and present in drinking water. In an era when people dependent upon locally-grown foods and drinking water, iodine deficiency (goiter) was a regional problem. Prior to the introduction of iodized salt in the US in the 1920s, 26-70% of children living in the Great Lakes, Appalachians, and Northwestern regions were estimated to have clinically apparent goiter. Today, the situation is much different with global distribution of foods and iodization of salt.
Despite iodization, 35% of the world population have inadequate iodine intakes. While 50-60% of Americans report using iodized salt in their homes, recommendations to decrease salt intake may push iodine intake down. This seems to be the case when the most prevalent micronutrient deficiency is iodine (Murphy et al, 2015; Bird et al, 2015).
The World Health Organization defines iodine status using urinary concentrations, preferably 24 h collections. For school-age children 6 years and older, an adequate iodine status is urinary iodine concentrations ranging between 100-199 ng/mL. For pregnant women, the adequate range is 150-249 ng/mL. The CDC’s Second Nutrition Report finds that American women 20-39y have the lowest urinary iodine status of all age groups. Wei and colleagues report that 48.3% of pregnant women in Shanghai China are iodine deficient (urinary iodine concentration < 150 µg/g creatinine). The iodine content of household salt and multivitamin supplements were the primary determinants of status.
In a new analysis of individuals living in Greenland, the accuracy of 24 hour and sport urine samples to assess iodine status are compared. A morning spot urine sample significantly underestimated iodine status, especially at higher concentrations (> 150 ug/d).
The reproducibility of this interpretation is questionable when 40% of the 24h collections appeared to be incomplete (measured by an indicator, PABA). It still seems that the best way to assess iodine status is with a 24h urine sample because it incorporates circadian variations in dietary intake and urinary excretion. However, indicators and spot samples are valuable when used appropriately.
Bottomline: Unless urinary iodine is measured, people cannot predict iodine status, especially without knowing if the salt used in food flavoring was iodized or not.
Andersen S, Waagepetersen R, Laurberg P. Misclassification of iodine intake level from morning spot urine samples with high iodine excretion among Inuit and non-Inuit in Greenland. 2015 Br J Nutr doi: 10.1017/S0007114515000653
Wei Z, Wang W, Zhang J, Zhang X, Jin L, Yu X. Urinary iodine level and its determinants in pregnant women of Shanghai, China. 2015 Br J Nutr doi: 10.1017/S0007114515000665
Murphy RA, Ciappio ED, Bird JK. Lower prevalence of vitamin and mineral deficiencies among adolescent users of full spectrum multivitamin/mineral supplements. 2015 FASEB Abstract 250.4
Bird JK, Ciappio ED, Murphy RA. Adult full spectrum multivitamin/mineral supplement users have a lower prevalence of vitamin and mineral deficiencies. 2015 FASEB Abstract 586.2
Leung AM, Braverman LE, Pearce EN. History of US iodine fortification and supplementation. 2012 Nutrients doi: 10.3390/nu4111740
Assessment of iodine deficiency disorders and monitoring their elimination. A guide for programme managers. Third edition (updated 1st September, 2008) ISBN 978 92 4 159582 7
Originally released on April 8, then updated and posted on April 9.