Iodine variability in retail cows’ milk among different retail outlets in the U.S.

Authors: ROSELAND, JANET - Consultant; PHILLIPS, KATHERINE - Virginia Tech; Vinyard, Bryan; TODOROV, TODOR - Food And Drug Administration(FDA); ERSHOW, ABBY - Consultant; Pehrsson, Pamela

Submitted to: Nutrients
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/4/2023
Publication Date: 7/8/2023
Citation: Roseland, J.M., Phillips, K.M., Vinyard, B.T., Todorov, T., Ershow, A.G., Pehrsson, P.R. 2023. Iodine variability in retail cows’ milk among different retail outlets in the U.S.. Nutrients. 15:3377. https://doi.org/10.3390/nu15143077.
DOI: https://doi.org/10.3390/nu15143077

Interpretive Summary: In a previous study, large variability in iodine content was found among samples of store brand retail milk in a single time point sampling from 24 nationwide U.S. locations for the USDA FoodData Central database, but the sampling plan was not designed to detect differences among locations. This follow-up study was done to evaluate possible differences among retail supplies. Milk samples (2% fat) were collected bimonthly in fourteen locations for one year and analyzed in duplicate, including control materials to support accuracy of results and precision across analytical batches. The overall mean iodine concentration was 82.5 µg/240 mL serving (SE 7.0), comparable to the previous national mean (85.0, SE 5.5) and with a similar wide range among individual samples (27.9-282). For some locations the mean iodine concentration differed significantly from others, and differed from the national average by amounts ranging from -47 µg to +37 µg per serving. The between-sample range within location was large for some (up to 229 µg/serving) and minimal for others (as little as 13.2 µg/serving) These findings suggest iodine intake from some retail milk supplies could be over- or underestimated relative to the national average, even if the latter is suitable for population-wide estimation of intake.

Technical Abstract: Iodine intake remains a current health concern. Milk is a common dietary iodine source in the U.S. This study investigated variability of iodine content in milk following a previous single point time national sampling, particularly whether iodine was different within a retail supply than the national average or among different retail supplies. Milk samples (2% fat) collected regularly in fourteen locations for one year were analyzed in duplicate using approved laboratory methodology with control materials. Quality control data supported accuracy of results, precision across batches, and minimal analytical uncertainty. Mean iodine concentration was 82.5 µg/240 mL serving (SE 7.0), similar to previous mean of 85 (SE 5.5). These results support the population-wide estimate of iodine contributed by milk using database values. Like the previous study, the 95% confidence interval for the mean was narrow. However, large differences occurred among many individual samples, ranging from 27.9 to 282 µg iodine/240 mL. Some retail outlets differed from other locations and the national average. Variance within location and among locations was notable in some cases. These observations suggest differences in iodine supplementation in feed and in milk processing. The iodine average for milk is reliable for nationwide estimates, but for clinical trials actual iodine content should be measured.