Large Variability of Iodine Content in Retail Cow's Milk in the U.S.

Iodine intake is of contemporary public health interest. The recommended daily iodine intake is 150 mu g for most adults, and milk is an important source of iodine in the U.S. diet. Iodine concentration in cow's milk is affected by diet and iodine supplementation levels, milking sanitation practices, and other factors. Current analytical iodine data in U.S. retail milk are crucial for evaluating population-wide health outcomes related to diet. Samples of whole (3.25% fat), 2%, 1%, and skim (0-0.5% fat) milk were procured from 24 supermarkets across the U.S. using a census-based statistical plan. Iodine was analyzed by inductively coupled plasma mass spectrometry, including certified reference materials and control samples to validate results. No difference in iodine content was found between milkfat levels (F-3,F-69 1.033, p = 0.4). Overall mean (SEM) was 85(5.5) mu g/serving (240 mL). However, the 95% prediction interval of 39-185 mu g/serving for individual samples indicated high variability among individual samples. Given the recommended 150 mu g iodine per day for most adults along with the study mean, one milk serving can provide approximately 57% of daily intake. Researchers, health care professionals, and consumers should be aware of iodine variability in milk, while additional research is needed to investigate the impact of iodine variability factors.