The percentage of Americans with low levels of iodine intake has more than quadrupled over the past 20 years. Iodine plays a role in the production of thyroid hormone, which is important in regulating various body functions. The authors point out that since iodine helps regulate hormones important to fetal and infant brain development, iodine deficiency is the world's leading cause of intellectual deficiency.

Beginning in the 1920s, US health officials mandated that all table salt in the US be fortified with iodine. The exact cause of the observed drop in intake levels remain unknown. The investigators note that the use of iodine as an ingredient in both bread and milk has been on the decline since the mid-1980s. They also speculate that many Americans, concerned about sodium's links to hypertension, may be cutting down on the amount of salt in their diet. Because iodine has been added to many brands of salt, they have also inadvertently cut down on their iodine intake.

Journal of Clinical Endocrinology and Metabolism October 1998;88:3401-3408.

COMMENT: Iodine is critical to thyroid function in adults. It is an important to confirm that you are getting adequate iodine in your diet.