Iodine Concentrations in US Milk: Variation Due to Time, Season, and Region

The iodine content of milk is influenced primarily by the iodine added to animal feed and by iodophor sanitizing solutions used in the dairy industry. Variability of these practices may result in variation of iodine concentrations in milk. Some seasonal and perhaps regional variation in iodine concentrations in milk may reflect the amount of indoor feeding (i.e., iodine supplemented feed) during the colder months versus outdoor pasture feeding during the warmer months. The proportion of indoor versus outdoor feeding depends upon the climate of the particular geographical area. Milks and other dairy products from the Food and Drug Administration's Total Diet Study were analyzed for iodine quarterly from 1982 to 1990. The iodine concentrations in fluid milks were evaluated over time, by season (summer, spring, winter, and fall), and by region (East, South, Central, and West). Iodine in fluid milks averaged 23 μg/100 g and ranged from 16 μg/100 g in the summer and fall in the East to 34 μg/100 g in the winter in the East. Iodine was highest in the winter (27 μg/100 g) and lowest in the summer (19 μg/100 g) and higher in western and central states (25 and 27 μg/100 g, respectively) than in eastern states (18 μg/100 g).