Sweating iodine

SAFETY PROFILE Experimental poison by subcutaneous route. Moderately toxic to humans by ingestion. Moderately toxic experimentally by ingestion, intraperitoneal, and intravenous routes. An experimental teratogen. Human systemic effects by multiple and unspecified routes toxic psychosis, excitement, respiratory stimulation, nausea or vomiting, and sweating. Experimental reproductive effects. Mutation data reported. A powerful irritant which affects the central nervous system. Incompatible with ferric salts, mineral acids, iodine, lead acetate, silver nitrate, sodium phosphate powder. When heated to decomposition it emits toxic fumes of Na20. 

Perhaps the most ambitious early effort of this type was the model of iodine metabolism developed by Douglas Riggs (1952). He presented a theoretical model that included ingestion of iodine as iodide, its absorption into the plasma, and transfer to the thyroid and other tissues, with loss through the kidneys, sweat and expired air. Within the thyroid gland, he described the organification of iodine and production of monoiodothyronine, diiodothyronine, and thyroxine (T4) on the framework of thyroglobufln. 

Table 59.2 Iodine in sweat measured over time in volunteers maintained under oontrol oonditions at a temperature of 38.5°C and relative humidity of 30%...

Sweat weight (g) Time (h) Iodine cone, (gg/l) Total iodine loss (iig)... 

Such losses may be negligible in those parts of the world where diets are iodine-replete and intrathyroidal iodine and thyroid hormone stores abundant. However, in areas of iodine deficiency, overt or borderline, the additional stress of iodine loss in sweat may have relevance to thyroid status (Smyth and Duntas, 2005). It is this possibility which is the subject of the present study. 

Studies by one of the authors in Ireland, an area of borderline dietary iodine intake, consistently showed a much lower level of iodine in sweat (19 8 pg/1). The percentage distribution of individual values is shown in histogram form in Figure 59.2. It can be seen that the majority of individual values (64.8%) lie between 20 and 30pg/l, with a median value of 20 pg/1. This is difficult to explain in the context of the apparent independence of sweat iodine content from dietary iodine intake reported by Mao et al. (1990). In order to study this phenomenon further volunteers were given 400 pg of KI orally before exercise and sweat samples were collected within one hour. As shown in Figure 59.3, this resulted in a doubling of sweat iodine from 20 to 40 pg/1 after 1 h, which returned to baseline 24 pg/1 after 24 h and increased to 32 pg/1 at 48 h. 

Table 59.3 Iodine loss (urine + sweat) in training athletes and controls...

Figure 59.2 Percent frequency distribution of sweat iodine levels (N = 43).

Figure 59.3 Sweat iodine vaiue foiiowing ingestion of Kl (400 (xg).

In the absence of definitive evidence that iodine loss through excessive sweating can induce a relative iodine deficiency with consequences for thyroid hormone formation, there is not as yet a case for iodine supplementation of those involved in vigorous exercise. However, the... 

Asa published sweat iodine concentration of35—40 p,g/l sweat losses of 4—5 liters would involve iodine losses equivalent to the WHO-recommended adult daily iodine intake ( 150 p,g). 

Iodine losses in sweat may not be independent of dietary iodine intake. 

Over a prolonged period of exercise, sweat iodine losses would result in a significant depletion of thyroidal iodine stores. 

Radioactive iodine is excreted primarily in the urine and in smaller amounts in saliva, sweat and feces. The contamination in sweat is small. According to the findings of Lassman et al. (1998) and Schomaecker et al. (2000), less than 0.1% is exhaled. Jacobson et al. (1978) have shown that internal doses resulting from contamination and intake of are likely to be much smaller (a factor of over 100) than external exposure to radiation from patients. Next to urine, the highest iodine excretion is in saliva. The activity in the salivary glands has been found to be proportional to the administered activity. In a study by O Doherty et al. (1993), it was shown that the maximal salivary activity occurs approximately 24 h post-administration. 

D. A bluish skin discoloration involving sweat glands may occur following large doses of iodine-containing products. 

ABSORPTION, METABOLISM, EXCRETION. Most of the iodide present in food is iodine, in which form it is absorbed. Absorption takes place in the small intestine. Following absorption, iodine takes two main pathways within the body. Approximately 30% is removed by the thyroid gland and used for the synthesis of the thyroid hormones most of the remainder is excreted in the urine, although small amounts are lost in the feces and sweat. 

Hyperthyroidism The result of excessive circulating thyroid hormone with nervousness, sweating, tremor, with a rapid heart rate and loss of weight ICCIDD International Council for Control of Iodine Deficiency Disorders-an international non-government organization made up of a network of 700 health professionals from more than 90 countries available to assist IDD elimination programs in affected countries... 

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