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    Should pregnant women receive iodine supplementation?

    Iodine deficiency is on the rise in the United States, thanks in part to changing dietary habits

     

    One of this nation’s greatest public health successes resulted from the decision to cheaply supplement table salt with iodine. Since iodine supplementation of our diets began in the 1920s, we in the United States have almost eliminated severe iodine deficiency. Before then, endemic iodine deficiency was prevalent in the so-called goiter belt--the Great Lakes, Appalachian, and Northwestern region--where 26% to 70% of children had clinically apparent goiter.1

    Iodine deficiency is still a major global health problem; approximately 2 billion people are currently at risk. It remains a leading cause of preventable mental retardation in children worldwide.2 In the past, the stigmata of iodine deficiency and the ensuing hypothyroid states could not be ignored. In addition to large goiters, affected women had pregnancy complications and their offspring had severe developmental delays. Fortunately, such overt clinical manifestations are vanishingly rare in this country today, but more subtle forms of iodine deficiency are on the rise and pose a potential risk to pregnant women and their fetuses. Thus, US obstetricians need to once again be concerned about maternal iodine deficiency.

    Thyroid hormone homeostasis in pregnancy

    Iodine is crucial to maintaining a euthyroid state because it forms the elemental backbone of both thyroxine (T4) and triiodothyronine (T3). Normal thyroid function is critical to energy homeostasis and metabolism as well as normal cognition and neurological functioning in adults and children. Pregnant women are particularly vulnerable to iodine deficiency because early pregnancy is characterized by a rapid surge in thyroid hormone production (and iodine requirements).3 Late pregnancy also stresses maternal iodine stores because of increased renal clearance. Normally this enhanced iodine demand is easily overcome by adequate iodine intake, but these changes can easily overwhelm a woman who begins pregnancy with borderline or low iodine stores.

    The increasing prevalence of iodine deficiency in pregnancy

    The World Health Organization recommends 250 µg of iodine daily for pregnant and lactating women while the Institute of Medicine recommends 220 µg daily during pregnancy and 290 µg daily during lactation.2 While achieving such intake levels was easily accomplished in the past, contemporary dietary trends are making it harder for US mothers to meet these recommendations. Currently, the major sources of dietary iodine are iodized salt/table salt, breads/grains, and dairy products.4 However, the current push to reduce salt intake in order to lower risks of hypertension and cardiovascular disease as well as increasing intake of noniodized salt from processed foods and sea salts or kosher salts have measurably reduced US dietary iodine intake.5,6

    Seafood is also an excellent source of iodine but reduced seafood consumption during pregnancy, caused by concerns about excess mercury ingestion, has further exacerbated reduced iodine intake in pregnant women. As a consequence of these cumulative trends, US iodine stores have dropped by 50% from 1970s levels when assessed by urinary iodine concentration (UIC), the most common method of evaluating iodine status in populations7 From 1971 to 1974, the median UIC was 320 µg/L, but by 2005 to 2008, the median UIC level had fallen to 164 µg/L.8 National survey data also suggest that among women of childbearing age, the median UIC decreased from 294 µg/L to 128 µg/L, and the most recent National Health and Nutrition Examination Survey (2003–2004) reported that 37.2% of women of childbearing age had UIC values below 100 µg/L, which suggests mild iodine deficiency.2,8

    NEXT: DOES MILD IODINE DEFICIENCY MATTER? >>

    Charles J. Lockwood, MD, MHCM
    Dr. Lockwood, Editor-in-Chief, is Dean of the Morsani College of Medicine and Senior Vice President of USF Health, University of South ...

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