Food Group Intakes as Determinants of Iodine Status among US Adult Population

Abstract

Adequate intake of iodine is essential for proper thyroid function. Although dietary reference intakes for iodine have been established, iodine intake cannot be estimated due to the lack of data on iodine contents in foods. We aimed to determine if food group intakes can predict iodine status assessed by urinary iodine concentration (UIC) from spot urine samples of 5967 US adults in the National Health and Nutrition Examination Survey (NHANES) 2007–2012. From an in-person 24-h dietary recall, all foods consumed were aggregated into 12 main food groups using the individual food code of the US Department of Agriculture (USDA); dairy products, meat/poultry, fish/seaweed, eggs, legumes/nuts/seeds, breads, other grain products, fruits, vegetables, fats/oils, sugars/sweets, and beverages. Chi-square test, Spearman correlation, and multiple linear regression analyses were conducted to investigate the predictability of food group intakes in iodine status assessed by UIC. From the multiple linear regressions, the consumption of dairy products, eggs, and breads, and iodine-containing supplement use were positively associated with UIC, whereas beverage consumption was negatively associated with UIC. Among various food group intakes, dairy product intake was the most important determinant of iodine status in both US men and women. Subpopulation groups with a high risk of iodine deficiency may need nutritional education regarding the consumption of dairy products, eggs, and breads to maintain an adequate iodine status. Efforts toward a better understanding of iodine content in each food and a continued monitoring of iodine status within US adults are both warranted.

Iodine Status and Consumption of Key Iodine Sources in the U.S. Population with Special Attention to Reproductive Age Women

“…Despite the lack of a publicly available national nutrient database with iodine values for foods and beverages consumed in the US, there is consistent agreement that dairy, grains, eggs, and fish provide the bulk of iodine in the US diet [ 18 , 30 , 48 ], as assessed through mUIC. We found that non-Hispanic Asian WRA, consumed similar amounts of dairy and grains when compared to non-Hispanic black WRA; yet the mUIC for non-Hispanic Asian WRA (81 mg/L) was significantly lower than their non-Hispanic black (124 mg/L) counterparts, and indicative of mild iodine deficiency.…”

“…Additionally, some reports have found bread, but not other grain products, to be a good source of dietary iodine. [ 11 , 18 ]. If the type of grain consumed is important, i.e., breads vs. rice, then the difference in mUIC between non-Hispanic Asian persons and non-Hispanic blacks, might be explained by different consumption patterns of rice vs. breads.…”

“…The iodine content in dairy milk can vary widely [ 15 ], depending on the iodine content in cattle feed, teat-dipping practices before and after milking [ 16 ], and the presence of goitrogens (substances that can block the uptake or utilization of iodine in cattle feed [ 17 ]). Other common food sources of iodine include grains and eggs [ 10 , 18 ].…”

“…Similar declines have been reported separately among men and women from 2001–2004 through 2009–2012 [ 27 ] and among pregnant women from the 1970s until 2007–2010 [ 28 ]. Iodine status may also be of concern among subgroups of the US population who report low consumption of dairy, eggs, and bread [ 18 , 29 , 30 ], key sources of iodine in the U.S. diet [ 10 ].…”

Development of Databases on Iodine in Foods and Dietary Supplements

“…The DSID assay results suggest that the actual iodine content for adult MVMs, pediatric MVMs, and non-prescription prenatal MVMs may typically exceed the labeled amount by 20–26%. Furthermore, comparisons of labeled iodine contents of prescription and non-prescription prenatal supplements sold in the US have found that, per tablet, non-prescription prenatals contain approximately 10% more iodine than prescription prenatals [ 99 , 100 ].…”