Monday, November 28, 2011

Iodine Deficiency

In the midst of moving I of course had to continue with my online graduate program.  Just after arriving here in MN I had a paper due discussing just about any topic of my choosing, but still relating to nutrition.  Being inspired by an article in Men's Health, I chose iodine deficiency.  Here I've included select portions from my paper.  Hope you learn something.... I sure did.

Approximately one-fourth of Americans suffers from hypertension, (blood pressure of 140/90mm Hg or greater) placing them at risk for coronary artery disease and stroke.  While medications such as Lasix are available and widely used, diet and lifestyle play a major role in the treatment of hypertension.  The DASH diet (Dietary Approaches to Stop Hypertension) has been promoted for many years, and is based upon the eating patterns of the Mediterranean population.  The diet is low in fat, cholesterol, and sodium; but promotes a high intake of fruits, vegetables, and whole grains.  This type of eating plan increases intake of potassium and calcium.  Both minerals appear to have antihypertensive properties.  Other lifestyle factors that influence blood pressure include body weight, physical fitness, and emotional/psychological stress.

Many Americans are becoming more aware of the complications associated with hypertension and have begun decreasing their use of table salt in an effort to cut out sodium.  However, is it possible that by cutting out salt, they are also cutting out an important nutrient, which may have cardiovascular benefits?  A recent Men’s Health Magazine article notes how the decline in table salt usage may be leading to an increase in iodine deficiency.  Salt was first iodized in 1924 in an effort to prevent mental retardation and goiter in the Midwest where these symptoms of iodine deficiency were quite common.  Today, people are switching to kosher and sea salt after watching famous Chef’s on TV use them.  Fast food restaurants, processed food companies often do not use iodized salt in their products.  Also, most Americans do not eat salt-water fish on a regular basis, further increasing the potential for iodine deficiency.  This is in direct conflict with Medeiros and Wildman who state that there is concern people in the United States may be over consuming iodine; thanks in part to the typically high sodium diets of Americans (pg 345).

Iodine is most often associated with the thyroid.  Iodine deficiency results in hypothyroidism, goiter, and cretinism. Thyroid hormones are not only integral to a person’s metabolism, but they also play a role in cardiovascular health including blood pressure and cholesterol levels.    Several literature reviews have compiled studies, which bring to light the connection between iodine deficiency, hypothyroidism, and the increased risk for cardiovascular disease.  Stephen A. Hoption Cann notes that, in recent years the prevalence of iodine deficiency has increased in many countries that use iodized salt, and that even subclinical levels of iodine deficiency can cause thyroid dysfunction leading to an increased risk for CVD

Ayturk and colleges studied the connections between metabolic syndrome and increased thyroid volume and nodule prevalence in people living in a previously iodine deficient area.  The study took place in Ankara, Turkey between August 2007 and February 2009.  Until 1999, Turkey was considered a moderately iodine deficient area, when mandatory iodization of household salt was initiated.  The researchers set out to discover if metabolic syndrome (MetS) is in fact not only linked to diet and lifestyle, but also associated with functional and morphological alterations in the thyroid gland.  

As expected, BMI, waist circumference, blood pressure, fasting blood glucose, fasting insulin, LDL-C, triglycerides, and fat mass were much higher in the MetS group than the control group.  HDL-C was lower in the MetS group.  FT3 and FT4 were not significantly different between the MetS group and the control group.  However, TSH levels, occurrence of thyroid nodules, and thyroid volume, were significantly higher in the MetS group than the control group.  All subjects including those in the control group were found to have increased thyroid volumes and nodule formations when insulin resistance was present.  Three study participants were found to have thyroid cancer, compared to the control group where no cancers were discovered.

In their discussion of the study, the researchers acknowledge the possible relationship between the hypothalamus-pituitary-thyroid axis and the influence of adipose tissue and leptin secretion on the axis.  They concluded that as fat mass increase, so does the excretion of leptin.  Insulin resistance causes an increase secretion of insulin, thereby increasing leptin levels further.  The increase in leptin and fat mass both stimulate an increase in TSH levels and ultimately induce further adipogenesis.   TSH is also involved in the regulation of thyroid growth.  The study did show that participants with elevated TSH levels were at risk for increased thyroid size but not thyroid nodules.

Unfortunately the researchers may have missed on very important aspect to their study, the actual intake of iodine by participants.  While Turkey may have previously been iodine deficient, the study was done 8 years after iodized-salt was introduced in the country.  It would have been beneficial to test participant’s iodine levels, as well as take a diet recall to assess their iodine intake.  The researchers proved that MetS and enlarged thyroids are related, but they failed to make any connection to their relationship with iodine intake.  This makes the title of their study somewhat misleading.  The only limitation mentioned is in connection to the small sample size found with thyroid cancer.  Because the detection rate was only 2.7% it is not considered statistically significant, and was not a main focus of the study.  Further studies should be done in this field in order to determine which came first MetS, or the enlarged thyroid.  If hypothyroidism is indeed a contributor to MetS, further studies into its root cause should be also done.  This may bring to light further information on iodine deficiency and it’s link to MetS and heart disease.

Ayturk, S., Gursoy, A., Kut, A., Anil, C., Nar, A., Tutuncu, N.B. (2009). Metabolic syndrome and its components are associated with increased thyroid volume and nodule prevalence in a mild-to-moderate iodine-deficient area. European Journal of Endocrinology. 161:599-605.

Cappola, Anne R., Ladenson, Paul W.  (2003). Hypothyroidism and Atherosclerosis. Journal of Clinical Endocrinology & Metabolism. 88(6):2438-2444.

Hoption Cann, Stephen A. (2006). Hypothesis: Dietary Iodine Intake in the Etiology of Cardiovascular Disease.  Journal of the American College of Nutrition. 25(1):1-11.

Medeiros, D. M., Wildman R.E.C. Avanced Human Nutrition, Second Edition. Jones & Bartlett Learning. 2012. Pg 73.

Rehagen, T. (2011, October). Do You Need More Salt?.  Men’s Health. 136-140.