Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc (2001) / Chapter Skim
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8 Iodine
8 Iodine
Pages 258-289
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From page 258... ...
BACKGROUND INFORMATION Function Iodine is an essential component of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3)
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From page 259... ...
Other brief reports have suggested that inacloquate iodine nutrition impairs immune response and may be associated with an increased inciclence of gastric cancer (Venturi et al., 1993~. While these other possibilities deserve further investigation, the overwhelming importance of nutritional iodine is as a component of the thyroid hormones.
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From page 260... ...
TSH affects several sites within the thyrocyte, the principal actions being to increase thyroidal uptake of iodine and to break clown thyroglobulin in order to release thyroid hormone into the circulation. An elevated serum TSH concentration indicates primary hypothyroidism, and a decreased TSH concentration shows hyperthyroidism.
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From page 261... ...
The Third National Nutrition and Health Examination Survey study of samples collected from 1988 to 1994 showoci a meclian urinary iodine excretion of 145 HAL, well above the lower level consiclereci to reflect adequate intake (100 ~g/L) (WHO Nutrition Unit, 1994)
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From page 262... ...
Major international efforts have produced dramatic improvements in the correction of iodine deficiency in the 1990s, mainly through use of iodized salt in iodine-deficient countries. SELECTION OF INDICATORS FOR ESTIMATING THE REQUIREMENT FOR IODINE Iodine Accumulation and Turnover The normal thyroid gland takes up the amount of circulating iodine necessary to make the proper amount of thyroid hormone for the body's needs.
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From page 263... ...
In populations with acloquate general nutrition, urinary iodine concentration correlates well with the urine iocline/creatinine ratio. Urinary iodine excretion is recommencleci by the World Health Organization, the International Council for the Control of Iodine Deficiency Disorders, and the United Nations Chilciren's Fund (WHO Nutrition Unit, 1994)
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From page 264... ...
As an example, urinary iodine excretion of 100 ~g/L in a 57-kg girl would indicate a daily iodine intake of 134 fig. Simple methods for measuring urinary iodine exist (Dunn et al., 1993~.
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From page 265... ...
A fourth limitation is that while studies such as these try to control intake, iodine appears in many unidentified or unrecognized substances that are ingested; therefore control of iodine intake in these studies would have been limited. Despite the limitations of balance studies, ciata from them were used for estimating the average requirement for iodine in children.
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From page 266... ...
Studies of groups with differing iodine intakes, as reflected in urinary iodine concentrations, show different mean serum TSH concentrations, although they may remain within the normal range. The sensitivity of TSH can be enhanced by previous stimulation with TSH-releasing hormone (TRH)
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From page 267... ...
Goitrogens Some foocis contain goitrogens, that is, substances that interfere with thyroid hormone production or utilization (Gaitan, 1989~. Examples include cassava, which may contain linamarin and is metabolizeci to thiocyanate which in turn can block thyroicial uptake of iodine; millet, some species of which contain goitrogenic substances; water, particularly from shallow or polluted streams and wells, which
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From page 268... ...
Iodine concentrations in human milk are influenced by maternal iodine intake (Gushurst et al., 1984~. The meclian iodine concentration in human milk of American women who consumed noniodized salt was 113 ~g/L, whereas the concentration in
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From page 269... ...
Baseci on the meclian intake of iodine consumed from human milk and the average urinary iodine excretion of the infant, the AI for infants ages O through 6 months has been set at 110 ~g/ciay. Ages 7 though 12 Months.
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From page 270... ...
The meclian iodine intake of the seven rehabilitated children was 63.5 ~g/ciay, and the average iodine balance was +19 ~g/ciay. The coefficient of variation (CV)
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From page 271... ...
Goiter prevalence in a population increases inversely with iodine intake. Because iodine deficiency is rare in the United States, ciata from Europe are used to relate goiter, as cletermineci by ultrasound, to urinary iodine excretion.
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From page 272... ...
3. Therefore, for a 10-year-olci child weighing 40 kg, the urinary iodine concentration of 100 ~g/L approximates a daily iodine intake of 125 fig (1.15 .
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From page 273... ...
A for Boys 9-13 years 14-18 years RI) A for Girls 9-13 years 14-18 years 90 1lg/day of iodine 90 1lg/day of iodine 120 1lg/day of iodine 150 1lg/day of iodine 120 1lg/day of iodine 150 ~g/day of iodine Adults Ages I 9 Years and folder Evidence Considered in Estimating the Average Requirement Thyroid Iodine Accumulation and Turnover.
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From page 274... ...
, thyroid hormone secretion (69 to 171 fig/ clay) cletermineci by using the method of Berson and Yalow (1954)
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From page 275... ...
Studies have measured thyroid volume by ultrasound and correlated it with urinary iodine excretion and the effects of iodine supplementation cluring pregnancy (Berghout and Wiersinga, 1998~. Pregnant women in an iodine-deficient area of Italy were given iodized salt estimated
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From page 276... ...
, pregnant women with an initial urinary iodine of 36 ~g/L were treated with an additional 100 g/day. Their median urinary iodine concentration increased to 100 ~g/L at 33 weeks, and their thyroid volume increased by 15 percent, compared with 30 percent in control subjects.
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From page 277... ...
RI) A for Lactation 14-18 years 19-30 years 31-50 years 290 1lg/day of iodine 290 1lg/day of iodine 290 1lg/day of iodine INTAKE OF IODINE Food Sources The iodine content in most food sources is low and can be affected by content of soil, irrigation, and fertilizers.
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From page 278... ...
Hazard Identification Most people are very tolerant of excess iodine intake from food (Pennington, 1990~. Certain subpopulations, such as those with autoimmune thyroid disease and iodine deficiency, respond adversely to intakes consiclereci safe for the general population.
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From page 279... ...
Laurberg and coworkers (1998) showoci that in populations with high iodine intake, impaired thyroid function (i.e., elevated TSH concentration)
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From page 280... ...
Seasonal variations in thyrotoxicosis have been related to variations in ciaily iodine intake from 126 to 195 fig to 236 to 306 fig (Nelson and Phillips, 1985~. Summary Challenged thyroid function shown by TSH concentrations elevateci over baseline is the first effect observed in iodine excess.
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From page 281... ...
Baseline urinary iodine excretion was 287 ~g/ciay; therefore baseline iodine intake from food is estimated to be approximately 300 ~g/ciay. The mean basal serum TSH concentration increased significantly in those receiving the two higher closes, although it remained within the normal range.
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From page 282... ...
Given the dearth of information, the UL values for children and adolescents are extrapolated from those established for adults. Thus, the adult UL of 1,100 ~g/ciay of iodine was acljusteci for children and adolescents on the basis of body weight as clescribeci in Chapter 2 and using reference weights from Chapter 1 (Table 1-1~.
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From page 283... ...
may have increased sensitivity to adverse effects of iodine intake. Some young adults with simple goiter and iodine deficiency who were supplementeci with 200 ~g/ciay of iodine clevelopeci either mild transient hyperthyroiclism or hypothyroidism, positive antibodies, and reversible histological changes of lymphocytic thyroiclitis (Kahaly et al., 1997~.
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From page 284... ...
· Effects of iodine concentration in water purification. · Further stanciarclization of thyroid volume by ultrasound and urinary iodine excretion in areas with different iodine intake.
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From page 285... ...
Evaluation of the iodine intake: Problems of the iodine/creatinine ratio Comparison with iodine excretion and daily fluctuations of iodine concen "ration. Exp Clin End ocrinol Diabetes 106: S 17-S20.
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From page 286... ...
1982. Influence of increasing iodine intake on thyroid function in euthyroid and hyperthyroid states.
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From page 287... ...
Trends and public health implications: Iodine excretion data from National Health and Nutrition Examination Surveys I and III (1971-1974 and 1988-1994~. ~ Clin Endocrinol Metab 83:34013408.
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From page 288... ...
1985. Seasonal variations in dietary iodine intake and thyrotoxicosis.
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From page 289... ...
1967. Iodine intake, excretion and thyroidal accumulation in healthy subjects.
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