Young American women of childbearing age have borderline levels of iodine, that is only just above what would be regarded as iodine deficiency, according to a new report released this week by the US Centers for Disease Control and Prevention (CDC). This age group (20 to 39 years of age) also had the lowest iodine levels of any age group of women, according to the CDC\'s Second National Report on Biochemical Indicators of Diet and Nutrition. Iodine is an essential nutrient that the body needs for healthy functioning of the thyroid, whose hormones help regulate growth and development. Women of childbearing age need a good supply of iodine for the healthy development of the fetus during pregnancy. Insufficient iodine leads to mental retardation, goiter (swelling in the thyroid gland), cretinism (stunted physical and mental growth), hypothyroidism (insufficient thyroid hormone) and other growth and development disorders. Dietary salt is one of the major sources of iodine in over 70 countries, including the US and Canada, that have salt iodization programs. Seaweed (eg kelp, nori, kombu, and wakame) is one of the richest food sources of dietary iodine. Other good food sources include seafood, dairy products, grains and eggs. Fruits and vegetables also contain iodine, but the amount varies according to the iodine content of the soil they grow in, and how they are fertilized and irrigated. Dairy products, especially milk, and grain products are the major contributors of iodine to the American diet. Pregnant women who do not consume enough dairy products may be particularly at risk of iodine deficiency, according to information from the Office of Dietary Supplements, part of the National Institutes of Health. A study published in 2010 by researchers at Central Michigan University suggests that iodine deficiency might be more likely among women who restrict their dietary salt intake than among women who don\'t. Overall, the CDC report finds that the US population has good levels of some essential vitamins and nutrients, but higher deficiency rates in some groups are a cause for concern. As well as highlighting the borderline iodine levels in childbearing age women, the report says Vitamin D deficiency is much higher in black Americans, and iron deficiency is higher among preschool Mexican-American children and non-Hispanic black and Mexican-American women of childbearing age.