Iodine is a chemical element and an important nutrient that the human body needs to produce hormones in the thyroid gland, an organ in the front of the neck. These thyroid hormones help regulate protein production, energy metabolism and normal growth and development. Iodine comes from a number of natural sources, such as milk. Without iodine, the human body may develop an iodine deficiency, which can lead to hypothyroidism, enlargement of the thyroid gland and mental retardation in children.
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Iodine in Milk
Milk is a natural source of iodine that helps provide the proper nutritional value for the cow's young. The iodine is present within the cattle feed that farmers give to the cows and eventually ends up in the milk. Other dairy products made from milk, such as cheese, frozen yogurt and ice cream, also contain iodine.
The amount of iodine may vary according to seasonal variations and the way in which the manufacturer prepares the milk. For example, the average iodine content in milk is significantly higher in winter than summer. It may also vary over time. Between 1965 and 1980, the iodine content of milk increased by 300 to 500 percent due largely to changes in cattle feeds. However, the limitations in the allowable amount of iodine to 10 mg per cow daily in 1986 actually resulted in a decrease of iodine in milk since then.
In 2004 a group of researchers from Boston Medical Center and Golestan University Medical School in Iran published a study in "The Journal of Clinical Endocrinology and Metabolism" that examined 18 brands of cow's milk. They found that all the samples had at least 88 micrograms of iodine per 250 ml — about a serving in size. Some samples had as much as 168 micrograms per serving. Infant formulae in the study ranged from 16.2 to 56.8 micrograms of iodine content per every 5 oz.
The Institute of Medicine has set a recommended dietary allowance of iodine at only 150 micrograms per day for adult men and women. For pregnant women the amount rises to 220 micrograms. Breastfeeding women need at least 290 micrograms a day. Milk represents a significant portion of the recommended daily intake of iodine for the U.S. population, and there is little danger of consuming too much iodine from milk. The Food and Nutrition Board sets an upper limit of the daily iodine intake at 1.1 mg, or 1,100 micrograms, for adults. However, it is possible to consume too much iodine with a certain combination of iodine-rich foods. Excessive iodine may not necessarily cause a dysfunction of the thyroid gland in people with normal-functioning thyroids, but can certainly cause problems in those with pre-existing thyroid conditions.