WEBVTT 1 00:00:00.600 --> 00:00:01.500 Hi all. 2 00:00:01.500 --> 00:00:03.630 In this lecture will be discussing the epidemiology 3 00:00:03.630 --> 00:00:04.953 of thyroid cancer. 4 00:00:06.690 --> 00:00:08.250 So we've several goals. 5 00:00:08.250 --> 00:00:09.750 We'll begin by describing the anatomy 6 00:00:09.750 --> 00:00:11.700 and function of the thyroid gland, 7 00:00:11.700 --> 00:00:13.590 looking at diseases of the thyroid gland, 8 00:00:13.590 --> 00:00:17.187 and then looking at hyperthyroidism and Graves' disease. 9 00:00:17.187 --> 00:00:20.293 We'll also discuss Hashimoto's thyroiditis, 10 00:00:20.293 --> 00:00:22.830 hypothyroidism and goiter. 11 00:00:22.830 --> 00:00:25.680 Finally, we'll look at studies of iodine supplementation. 12 00:00:26.520 --> 00:00:27.588 So to begin with, 13 00:00:27.588 --> 00:00:32.190 let's look at the anatomy of the thyroid gland. 14 00:00:32.190 --> 00:00:34.380 So the thyroid gland produces iodine-containing 15 00:00:34.380 --> 00:00:38.873 thyroid hormones like triiodothyronine or T3 16 00:00:38.873 --> 00:00:42.066 and thyroxine or T4. 17 00:00:42.066 --> 00:00:44.340 These circulating hormones are essential 18 00:00:44.340 --> 00:00:47.130 in regulating the rate of metabolism in the body. 19 00:00:47.130 --> 00:00:50.490 Inside the cell, T3 and T4 stimulate energy production 20 00:00:50.490 --> 00:00:51.480 by the mitochondria 21 00:00:51.480 --> 00:00:54.180 and promote glucose metabolism, protein synthesis, 22 00:00:54.180 --> 00:00:59.160 lipolysis, and excretion of cholesterol. 23 00:00:59.160 --> 00:01:00.990 Thyroid hormones also influence growth 24 00:01:00.990 --> 00:01:02.100 and development in early life 25 00:01:02.100 --> 00:01:04.650 and help maintain normal cardiac rhythm, muscle tone 26 00:01:04.650 --> 00:01:07.623 and neuronal function in the sympathetic nervous system. 27 00:01:08.490 --> 00:01:10.800 Biosynthesis of thyroid hormones is regulated 28 00:01:10.800 --> 00:01:12.972 by peptide hormones secreted by the hypothalamus 29 00:01:12.972 --> 00:01:15.600 and the anterior pituitary gland 30 00:01:15.600 --> 00:01:18.240 in response to low blood levels of thyroid hormones 31 00:01:18.240 --> 00:01:20.251 or neurological signals. 32 00:01:20.251 --> 00:01:23.653 Special cells of the thyroid gland called C cells 33 00:01:23.653 --> 00:01:28.355 produce a polypeptide hormone called calcitonin 34 00:01:28.355 --> 00:01:31.320 which helps regulate calcium homeostasis 35 00:01:31.320 --> 00:01:33.000 throughout the body. 36 00:01:33.000 --> 00:01:35.100 Relatively small parathyroid glands, 37 00:01:35.100 --> 00:01:36.660 usually four in number, 38 00:01:36.660 --> 00:01:39.425 are located at the periphery of the thyroid gland. 39 00:01:39.425 --> 00:01:43.620 The parathyroid glands synthesize parathyroid hormone, 40 00:01:43.620 --> 00:01:45.973 or PTH, which together with calcitonin 41 00:01:45.973 --> 00:01:49.020 and the active form of vitamin D, regulate levels of calcium 42 00:01:49.020 --> 00:01:50.820 and phosphorus in the blood, the bones, 43 00:01:50.820 --> 00:01:52.695 and most other tissues. 44 00:01:52.695 --> 00:01:57.600 So there's several kinds of neoplasms of the thyroid gland. 45 00:01:57.600 --> 00:02:01.710 To begin with, benign thyroid adenomas are relatively common 46 00:02:01.710 --> 00:02:03.960 and are detected approximately three times more often 47 00:02:03.960 --> 00:02:05.670 in women than men. 48 00:02:05.670 --> 00:02:07.380 Approximately 90 to 95% 49 00:02:07.380 --> 00:02:09.480 of solitary thyroid nodules are benign 50 00:02:09.480 --> 00:02:11.520 and are treated by simple excision. 51 00:02:11.520 --> 00:02:13.878 Treatment by simple excision is curative. 52 00:02:13.878 --> 00:02:16.740 Careful histological examination of tissue is always 53 00:02:16.740 --> 00:02:19.443 necessary to rule out malignant transformation. 54 00:02:20.280 --> 00:02:22.417 Malignant tumors of the thyroid gland are rare, 55 00:02:22.417 --> 00:02:25.200 but all thyroid nodules must be carefully examined 56 00:02:25.200 --> 00:02:26.940 under the microscope to distinguish benign 57 00:02:26.940 --> 00:02:28.653 from malignant tumors. 58 00:02:29.610 --> 00:02:32.280 Thyroid carcinomas arise from the cuboidal epithelium 59 00:02:32.280 --> 00:02:34.775 that lines the thyroid follicles. 60 00:02:34.775 --> 00:02:38.850 During 2000 and 2020 or during 2000 and 2012, 61 00:02:38.850 --> 00:02:40.320 the annual number of incident cases 62 00:02:40.320 --> 00:02:42.570 of thyroid cancer detected in the world population 63 00:02:42.570 --> 00:02:44.370 has increased dramatically, 64 00:02:44.370 --> 00:02:46.937 whereas the number of deaths has changed very little. 65 00:02:46.937 --> 00:02:48.420 Age-adjusted incidents 66 00:02:48.420 --> 00:02:51.030 and mortality rates actually show inverse trends. 67 00:02:51.030 --> 00:02:54.779 During 2002 to 2012, the incidents doubled among women, 68 00:02:54.779 --> 00:02:58.530 whereas the mortality declined by 25%. 69 00:02:58.530 --> 00:03:00.450 The inverse trends of incidents and mortality 70 00:03:00.450 --> 00:03:02.730 may largely reflect the increased early detection 71 00:03:02.730 --> 00:03:05.040 of small papillary thyroid tumors 72 00:03:05.040 --> 00:03:08.043 that are treated by complete surgical resection. 73 00:03:09.311 --> 00:03:14.100 During 2012, almost 300,000 new cases were diagnosed 74 00:03:14.100 --> 00:03:15.510 in the world population, 75 00:03:15.510 --> 00:03:18.599 and almost 40,000 people died from thyroid cancer. 76 00:03:18.599 --> 00:03:23.599 Of these, 77% of cases and 68% of deaths occurred in women. 77 00:03:23.884 --> 00:03:26.760 The annual age-adjusted incidence rate in 2012 78 00:03:26.760 --> 00:03:29.700 among women was 60.1 cases per 100,000 79 00:03:29.700 --> 00:03:32.133 compared to 1.9 per 100,000 in men, 80 00:03:33.960 --> 00:03:36.390 Incidence rates are markedly higher 81 00:03:36.390 --> 00:03:38.130 in high income countries 82 00:03:38.130 --> 00:03:39.960 than low and middle income countries. 83 00:03:39.960 --> 00:03:41.640 For example, the incidence in American 84 00:03:41.640 --> 00:03:44.460 and Canadian women is 10 to 20 times higher 85 00:03:44.460 --> 00:03:46.740 than the incidence rates among women living in India 86 00:03:46.740 --> 00:03:48.720 and sub-Saharan Africa. 87 00:03:48.720 --> 00:03:50.250 In contrast, mortality rates 88 00:03:50.250 --> 00:03:52.050 of thyroid cancer are markedly higher 89 00:03:52.050 --> 00:03:54.217 in less-developed regions of the world. 90 00:03:54.217 --> 00:03:57.300 For example, the mortality rates range from one 91 00:03:57.300 --> 00:03:59.030 to three deaths per 100,000 among women 92 00:03:59.030 --> 00:04:00.510 in sub-Saharan Africa, 93 00:04:00.510 --> 00:04:03.360 compared to 0.3 deaths per 100,000 among women 94 00:04:03.360 --> 00:04:04.863 in Canada and the US. 95 00:04:04.863 --> 00:04:08.550 In 2020, the overall age-standardized incidence 96 00:04:08.550 --> 00:04:11.324 of thyroid cancer was 6.6 per 100,000. 97 00:04:11.324 --> 00:04:13.140 Though as previously mentioned, 98 00:04:13.140 --> 00:04:15.341 the rate is much higher in women than men. 99 00:04:15.341 --> 00:04:18.859 The age-standardized mortality rate is 0.43 100 00:04:18.859 --> 00:04:21.510 per 100,000 people overall globally, 101 00:04:21.510 --> 00:04:23.070 but the mortality rate is slightly higher 102 00:04:23.070 --> 00:04:24.220 than women than in men. 103 00:04:25.710 --> 00:04:27.720 The annual incidence of thyroid cancer in the US 104 00:04:27.720 --> 00:04:31.177 during 1996 to 2000 was 68 cases per million. 105 00:04:31.177 --> 00:04:32.850 The female to male ratio 106 00:04:32.850 --> 00:04:34.979 of thyroid cancer is approximately three to one, 107 00:04:34.979 --> 00:04:38.195 and the annual incidence rates are highest in Hawaii 108 00:04:38.195 --> 00:04:42.099 where rates are one point or 119 per million in women 109 00:04:42.099 --> 00:04:43.635 and 45 per million, 110 00:04:43.635 --> 00:04:47.250 119 per million in women, and 45 per million in men. 111 00:04:47.250 --> 00:04:49.080 And the lowest in Poland 112 00:04:49.080 --> 00:04:51.558 where the rates are 14 per million in women 113 00:04:51.558 --> 00:04:52.836 and four per million in men. 114 00:04:52.836 --> 00:04:55.530 As shown in this figure, the annual incidence 115 00:04:55.530 --> 00:04:58.380 of thyroid cancer in the US increased 142% 116 00:04:58.380 --> 00:05:00.510 during 1973 to 2000, 117 00:05:00.510 --> 00:05:04.657 from 3.6 per 100,000 to 8.7 per 100,000. 118 00:05:04.657 --> 00:05:07.650 This increase was almost entirely attributed 119 00:05:07.650 --> 00:05:09.438 to the corresponding 185% increase 120 00:05:09.438 --> 00:05:12.358 in the incidence of papillary thyroid carcinoma 121 00:05:12.358 --> 00:05:17.358 from 2.7 per 100,000 to 7.7 per 100,000. 122 00:05:17.460 --> 00:05:18.363 In contrast, 123 00:05:18.363 --> 00:05:21.870 the incidence of follicular thyroid carcinoma did not change 124 00:05:21.870 --> 00:05:23.610 during the study period, and the mortality rates 125 00:05:23.610 --> 00:05:25.410 of thyroid cancer actually declined 126 00:05:25.410 --> 00:05:28.680 from 0.57 per 100,000 to, in 1973, 127 00:05:29.617 --> 00:05:33.690 to 0.47 per 100,000 in 2003. 128 00:05:33.690 --> 00:05:35.130 The observed trends are explainable 129 00:05:35.130 --> 00:05:36.510 by the increased early detection 130 00:05:36.510 --> 00:05:38.970 of small papillary thyroid tumors that were treated 131 00:05:38.970 --> 00:05:41.433 by complete surgical removal. 132 00:05:42.780 --> 00:05:44.910 Thyroid cancer, as well as other thyroid disorders, 133 00:05:44.910 --> 00:05:46.710 are more prominent in women. 134 00:05:46.710 --> 00:05:48.900 Since women seek medical attention more often than men, 135 00:05:48.900 --> 00:05:51.000 they may be more likely than men to undergo screening 136 00:05:51.000 --> 00:05:53.910 and diagnostic procedures that can detect thyroid nodules 137 00:05:53.910 --> 00:05:56.313 and other disorders of the thyroid gland. 138 00:05:57.837 --> 00:05:59.160 The incidence 139 00:05:59.160 --> 00:06:01.320 of thyroid malignancies is significantly increased 140 00:06:01.320 --> 00:06:03.810 in populations exposed to excessive radioactive fallout 141 00:06:03.810 --> 00:06:06.600 in Japan, following the atomic bombing in World War II 142 00:06:06.600 --> 00:06:10.320 and in Russia after the Chernobyl nuclear reactor accident. 143 00:06:10.320 --> 00:06:12.018 Longitudinal studies of populations exposed 144 00:06:12.018 --> 00:06:13.800 to radiation fallout indicate 145 00:06:13.800 --> 00:06:16.200 that diets deficient in iodine potentiate the risk 146 00:06:16.200 --> 00:06:18.630 of radiation-induced thyroid cancer 147 00:06:18.630 --> 00:06:20.340 and suggest that iodine supplementation 148 00:06:20.340 --> 00:06:23.457 has a protective effect against carcinogenesis. 149 00:06:23.457 --> 00:06:26.700 One study, a case control study looking 150 00:06:26.700 --> 00:06:29.070 at thyroid cancer and exposure to radioactive fallout 151 00:06:29.070 --> 00:06:31.355 from the Chernobyl nuclear reactor accident, 152 00:06:31.355 --> 00:06:33.540 in combination with dietary intake 153 00:06:33.540 --> 00:06:36.573 of iodine supplements, 154 00:06:38.310 --> 00:06:43.220 found that the overall risk of thyroid cancer increased 155 00:06:43.220 --> 00:06:46.877 with increasing doses of radioactivity. 156 00:06:46.877 --> 00:06:50.670 But subjects with low iodine intake had high, 157 00:06:50.670 --> 00:06:55.277 a higher odds ratio of developing cancer 158 00:06:55.277 --> 00:06:58.052 than those with similar radiation exposures 159 00:06:58.052 --> 00:07:01.413 and increased potassium iodine supplementation. 160 00:07:05.820 --> 00:07:08.970 Another potential risk factor is obesity. 161 00:07:08.970 --> 00:07:11.190 So, one case control study conducted in Hawaii 162 00:07:11.190 --> 00:07:13.230 found the risk of thyroid cancer increased 163 00:07:13.230 --> 00:07:16.170 with increasing body weight in both men and women. 164 00:07:16.170 --> 00:07:18.000 However, additional investigations are needed 165 00:07:18.000 --> 00:07:20.490 in order to clarify the impact of radiation, iodine, 166 00:07:20.490 --> 00:07:21.930 body mass, female reproduction, 167 00:07:21.930 --> 00:07:22.860 and other risk factors 168 00:07:22.860 --> 00:07:25.923 on thyroid carcinogenesis in different populations. 169 00:07:27.150 --> 00:07:28.890 The most commonly encountered diseases 170 00:07:28.890 --> 00:07:30.690 of the thyroid gland include either, 171 00:07:30.690 --> 00:07:34.200 involve either an overactive gland known as hyperthyroidism 172 00:07:34.200 --> 00:07:37.340 or an underactive gland known as hypothyroidism. 173 00:07:37.340 --> 00:07:40.020 The most prevalent thyroid condition is enlargement 174 00:07:40.020 --> 00:07:42.750 of the thyroid gland, which is called a goiter. 175 00:07:42.750 --> 00:07:45.630 Thyroid adenomas or nodules occasionally arise 176 00:07:45.630 --> 00:07:47.200 within the thyroid gland, 177 00:07:47.200 --> 00:07:49.710 and on pathologic examination, 178 00:07:49.710 --> 00:07:52.660 the vast majority of thyroid nodules turn out to be benign. 179 00:07:53.670 --> 00:07:55.620 Several non-malignant thyroid disorders 180 00:07:55.620 --> 00:07:57.840 have been found to be associated with thyroid cancer. 181 00:07:57.840 --> 00:07:59.550 The most prominent of these associations 182 00:07:59.550 --> 00:08:01.800 involve autoimmune conditions 183 00:08:01.800 --> 00:08:04.140 and auto-antibodies against thyroglobulin 184 00:08:04.140 --> 00:08:06.400 and other thyroid-specific factors. 185 00:08:06.400 --> 00:08:08.658 Thyroiditis refers to an inflammatory condition 186 00:08:08.658 --> 00:08:10.301 of a thyroid gland. 187 00:08:10.301 --> 00:08:12.442 Thyroiditis can lead to hyperthyroidism 188 00:08:12.442 --> 00:08:13.980 as in Graves' disease 189 00:08:13.980 --> 00:08:18.980 or hypothyroidism like in Hashimoto's thyroiditis. 190 00:08:19.200 --> 00:08:21.060 These inflammatory conditions are believed 191 00:08:21.060 --> 00:08:23.040 to have an autoimmune basis, and both have been linked 192 00:08:23.040 --> 00:08:25.940 to the development of thyroid adenomas and thyroid cancer. 193 00:08:26.970 --> 00:08:30.930 Hyperthyroidism refers to an overactive thyroid. 194 00:08:30.930 --> 00:08:32.880 Symptoms of this are due to the overproductive 195 00:08:32.880 --> 00:08:36.301 of thyroid hormones T3 and T4 by the thyroid gland. 196 00:08:36.301 --> 00:08:38.340 The most common cause 197 00:08:38.340 --> 00:08:41.825 of hyperthyroidism is a condition called Graves' disease. 198 00:08:41.825 --> 00:08:45.990 Graves' disease, also called diffuse toxic goiter, 199 00:08:45.990 --> 00:08:46.920 is believed to arise 200 00:08:46.920 --> 00:08:49.590 as a consequence of autoimmune reactions. 201 00:08:49.590 --> 00:08:52.230 This disease affects approximately 0.5% 202 00:08:52.230 --> 00:08:54.270 of the US population and is the underlying cause 203 00:08:54.270 --> 00:08:57.513 of up to 80% of all cases of hyperthyroidism. 204 00:08:58.350 --> 00:08:59.790 The clinical signs and symptoms 205 00:08:59.790 --> 00:09:01.920 of this condition result from excess stimulation 206 00:09:01.920 --> 00:09:03.750 of the thyroid gland by auto-antibodies, 207 00:09:03.750 --> 00:09:06.993 resulting in overproduction of T3 and T4 hormones. 208 00:09:07.890 --> 00:09:10.678 The peak incidence of Graves' disease is between 20 209 00:09:10.678 --> 00:09:12.990 and 40 years of age and symptoms include enlargement 210 00:09:12.990 --> 00:09:16.290 of the thyroid gland, protruding eyes, palpitations, 211 00:09:16.290 --> 00:09:18.810 excess sweating, diarrhea, weight loss, muscle weakness, 212 00:09:18.810 --> 00:09:21.300 and unusual sensitivity to heat. 213 00:09:21.300 --> 00:09:24.810 And it's five to 10 times more commonly diagnosed in women 214 00:09:24.810 --> 00:09:25.643 than in men. 215 00:09:26.490 --> 00:09:27.461 Genetic studies suggest 216 00:09:27.461 --> 00:09:31.100 that Graves' disease has a significant heredity component. 217 00:09:31.100 --> 00:09:34.050 An association between Graves disease 218 00:09:34.050 --> 00:09:35.790 and the development of thyroid cancer was reported 219 00:09:35.790 --> 00:09:39.573 more than 60 years ago in a 1948 article. 220 00:09:41.334 --> 00:09:45.060 A review of the malignancy rate in multiple studies 221 00:09:45.060 --> 00:09:47.940 of surgically resected thyroid nodules suggests 222 00:09:47.940 --> 00:09:50.762 that it's approximately 1.7 to 2.5% of nodules 223 00:09:50.762 --> 00:09:54.210 from Graves' disease patients manifest thyroid cancer, 224 00:09:54.210 --> 00:09:57.120 compared to only 0.25% nodules from other patients, 225 00:09:57.120 --> 00:09:59.359 reflecting a seven to 10 fold increased risk 226 00:09:59.359 --> 00:10:03.753 of thyroid cancer among patients with Graves' disease. 227 00:10:04.950 --> 00:10:06.958 Next, return to Hashimoto's thyroiditis, 228 00:10:06.958 --> 00:10:09.600 we see that it's a chronic autoimmune disease 229 00:10:09.600 --> 00:10:11.460 in which the thyroid gland is gradually destroyed 230 00:10:11.460 --> 00:10:13.710 by auto-antibodies against thyroglobulin 231 00:10:13.710 --> 00:10:16.980 or other cellular components of the thyroid gland. 232 00:10:16.980 --> 00:10:19.650 Patients often have a family history of thyroid disorders 233 00:10:19.650 --> 00:10:20.640 including Graves' disease 234 00:10:20.640 --> 00:10:23.018 and other autoimmune conditions 235 00:10:23.018 --> 00:10:24.750 such as type one diabetes, celiac disease 236 00:10:24.750 --> 00:10:27.090 pernicious anemia, Addison's disease, 237 00:10:27.090 --> 00:10:29.940 and Sjogren's syndrome. 238 00:10:29.940 --> 00:10:32.160 Hashimoto's thyroiditis is typically diagnosed 239 00:10:32.160 --> 00:10:34.110 between the ages of 45 and 65 years 240 00:10:34.110 --> 00:10:37.830 and occurs 10 to 20 times more often in women than in men. 241 00:10:37.830 --> 00:10:39.390 Patients are at increased risk 242 00:10:39.390 --> 00:10:40.470 of developing thyroid cancer 243 00:10:40.470 --> 00:10:43.610 compared to patients with thyroid nodules. 244 00:10:43.610 --> 00:10:45.810 In a metaanalysis of 38 studies, 245 00:10:45.810 --> 00:10:48.360 pathologic evidence of Hashimotos thyroiditis was present 246 00:10:48.360 --> 00:10:52.410 in 40.5% of the cases with thyroid cancer 247 00:10:52.410 --> 00:10:55.440 compared to only 21% of the controls 248 00:10:55.440 --> 00:10:57.153 with benign thyroid nodules. 249 00:10:59.208 --> 00:11:03.527 Next to turn to human leukocyte antigen or HLA, 250 00:11:03.527 --> 00:11:06.000 we see that genes of HLA play a major role 251 00:11:06.000 --> 00:11:08.292 in the immune response to foreign antigens 252 00:11:08.292 --> 00:11:09.930 as well as to the recognition of self versus non-self 253 00:11:09.930 --> 00:11:11.820 in immune reactions. 254 00:11:11.820 --> 00:11:14.070 The two classical forms of thyroiditis are known 255 00:11:14.070 --> 00:11:15.600 to have an autoimmune basis, 256 00:11:15.600 --> 00:11:18.117 Graves' disease and Hashimoto's thyroiditis. 257 00:11:18.117 --> 00:11:20.790 And genetic variants at the HLA locus appear 258 00:11:20.790 --> 00:11:23.673 to increase susceptibility to both conditions. 259 00:11:30.360 --> 00:11:33.210 Hypothyroidism refers to an underactive thyroid gland 260 00:11:33.210 --> 00:11:37.220 that results in a deficiency of thyroid hormones T3 and T4. 261 00:11:37.220 --> 00:11:38.910 Hypothyroid disorders occur 262 00:11:38.910 --> 00:11:41.100 when the thyroid gland is inactive or underactive 263 00:11:41.100 --> 00:11:43.500 as a result of improper formation from birth, 264 00:11:43.500 --> 00:11:45.210 lack of iodine or removal, 265 00:11:45.210 --> 00:11:48.573 and iatrogenic inactivation of the thyroid gland. 266 00:11:49.410 --> 00:11:52.260 Symptoms of hypothyroidism include abnormal weight gain, 267 00:11:52.260 --> 00:11:54.355 fatigue, baldness, temperature intolerance, 268 00:11:54.355 --> 00:11:57.183 and in some cases thyroid enlargement. 269 00:12:01.559 --> 00:12:04.740 Cretinism is an anomaly that is caused by iodine deficiency 270 00:12:04.740 --> 00:12:06.480 in the developing fetus. 271 00:12:06.480 --> 00:12:08.970 This devastating condition typically manifests at birth 272 00:12:08.970 --> 00:12:11.880 or during infancy and is characterized by hypothyroidism, 273 00:12:11.880 --> 00:12:15.540 goiter, intellectual developmental disabilities, 274 00:12:15.540 --> 00:12:19.140 deaf-mutism, stunted growth, and other anomalies. 275 00:12:19.140 --> 00:12:20.762 Endemic cretinism was once common 276 00:12:20.762 --> 00:12:23.280 in the Alpine populations of Southern Europe 277 00:12:23.280 --> 00:12:25.624 due to lack of iodine in their diets. 278 00:12:25.624 --> 00:12:27.780 And populations living in those areas 279 00:12:27.780 --> 00:12:30.120 without outside food sources are therefore at high risk 280 00:12:30.120 --> 00:12:32.620 for the development of iodine deficiency diseases. 281 00:12:33.504 --> 00:12:35.370 The addition of iodine to table salt 282 00:12:35.370 --> 00:12:38.283 has virtually eliminated cretinism in developed countries. 283 00:12:39.210 --> 00:12:43.080 Early detection of thyroid insufficiency in newborns 284 00:12:43.080 --> 00:12:46.950 and administration of thyroxine or T4 can often be effective 285 00:12:46.950 --> 00:12:48.570 in reinstating thyroid function 286 00:12:48.570 --> 00:12:50.640 and normal growth and development. 287 00:12:50.640 --> 00:12:53.432 Nevertheless, in lower middle income countries 288 00:12:53.432 --> 00:12:54.265 without such programs, 289 00:12:54.265 --> 00:12:56.370 the lack of dietary iodine remains the leading cause 290 00:12:56.370 --> 00:13:00.600 of preventable mental disability 291 00:13:00.600 --> 00:13:02.523 in babies and small children. 292 00:13:05.130 --> 00:13:07.260 In the US, iodized table salt 293 00:13:07.260 --> 00:13:10.830 containing 100 milligrams per kilogram of potassium iodine 294 00:13:10.830 --> 00:13:13.663 has been available since 1924. 295 00:13:13.663 --> 00:13:16.140 The US Food and Drug Administration recommends 296 00:13:16.140 --> 00:13:20.269 150 micrograms of iodine per day for both men and women. 297 00:13:20.269 --> 00:13:23.310 So supplementing the diet with iodized salt is a simple, 298 00:13:23.310 --> 00:13:27.903 cost effective method of ensuring adequate iodine intake. 299 00:13:31.632 --> 00:13:34.260 Goitrogens are dietary agents that suppress thyroid function 300 00:13:34.260 --> 00:13:36.240 and induce the formation of goiters, 301 00:13:36.240 --> 00:13:37.683 particularly in children. 302 00:13:41.790 --> 00:13:43.380 There also are some studies that suggest 303 00:13:43.380 --> 00:13:46.110 that high dietary intake of iodine may be associated 304 00:13:46.110 --> 00:13:47.670 with the development of thyroiditis, 305 00:13:47.670 --> 00:13:50.733 papillary thyroid carcinoma, and thyroid lymphoma. 306 00:13:53.940 --> 00:13:57.037 There also are some genetic characteristics 307 00:13:57.037 --> 00:13:59.523 to medullary thyroid cancer. 308 00:14:02.640 --> 00:14:06.210 Another rare form of cancer is parathyroid cancer, 309 00:14:06.210 --> 00:14:09.930 and it is approximately 1% of all cases 310 00:14:09.930 --> 00:14:13.743 of parathyroidism and about 0.005% of all cancers. 311 00:14:16.246 --> 00:14:18.930 Key steps to take for prevention of thyroid cancer 312 00:14:18.930 --> 00:14:20.640 are total avoidance of radiation exposure 313 00:14:20.640 --> 00:14:22.020 to the head and neck, 314 00:14:22.020 --> 00:14:25.560 maintenance of normal thyroid function by intaking iodine, 315 00:14:25.560 --> 00:14:29.100 avoiding goitrogens in the diet, like soy products, 316 00:14:29.100 --> 00:14:32.220 and regular checkups by ultrasonography to detect nodules 317 00:14:32.220 --> 00:14:35.280 and other abnormalities of the thyroid gland. 318 00:14:35.280 --> 00:14:37.399 Finally, a therapy for thyroid cancer 319 00:14:37.399 --> 00:14:42.000 includes early detection coupled with complete excision. 320 00:14:42.000 --> 00:14:44.670 There's a greater than 95% five year survival rate 321 00:14:44.670 --> 00:14:46.533 for patients with stage one disease.