Iodine, a trace element, is essential for the regulation of thyroid hormones, and is needed by the reproductive system. It also plays a role in normal growth and development. Iodine deficiency at an early age can cause anything from cretinism with mental retardation to a small enlargement of the thyroid. To avoid Iodine deficiency, make sure to use iodized salt in your meals.

References:

• National Research Council. Recommended Dietary Allowances, 10th Edition. Washington: 1989.
• Brody, Jane. Jane Brody's Nutrition Book. Bantam Books. 1987.