Iodine dietary recommendations

Levander OA, Whanger PD. 1996. Deliberations and evaluations of the approaches, endpoints and paradigms for selenium and iodine dietary recommendations. J Nutr 126(Suppl.) 2427-2434. 

From this brief overview, it is clear that dietary recommendations to increase iodine intakes in pregnancy need to be country- or region-specific. A well-estabHshed iodine... 

These are classified as those with a requirement below one pg (microgram) per day. Elements in this class include boron, chromium, fluoride, iodine, molybdenum, nickel, selenium, cobalt and manganese. Cobalt is part of vitamin (see above). However, there appear to be no recommended dietary intakes for any of these except molybdenum. 

The thyroid hormones T4 and T3 contain 65% and 59% of iodine respectively as an essential component for biological activity of the molecule. Iodine from dietary sources or medication enters the body via gastrointestinal tract. The recommended daily adult intake is 150-300 pg. Iodine is rapidly absorbed and enters the extracellular fluid pool. Iodide is removed from the blood largely by the thyroid and kidneys. The higher the intake the lower the fractional iodine uptake by the thyroid. 

The recommended dietary iodine intakes represent amounts of iodine sufficient to prevent symptoms of deficiency and impairment of health or performance while maintaining the body s store of iodine (see sections Requirements/ Recommendations for Iodine Supplementation and Response Criteria and Dose—Response Studies of Iodine Requirement in Farm Animals ). Recommended daily... 

However, as explained below, the oxazolidinethiones must be eliminated by oxidation and impair iodine and thyroid hormone status. Large doses of methimazole or methylthiouracil( 1000 mg/kg diet approximatelyd 5 mg/kg BW/day) also impair thyroid hormone production and do not respond to dietary iodine supplementation. After exposure to methimazole or methylthiouracil for several weeks, the pigs developed severe hypothyroidism. This did not respond to iodine supplementation, even at doses significantly above the recommended amounts (Hennig et al., 1969 Schone et al., 1997a). 

In a substudy of MoBa, including pregnant women grouped as users or nonusers of vitamin and mineral supplements, median urinary iodine excretion per 24 h was 190p,g and 110p,g, respectively (Brantsaeter et al., 2007). In the same study, dietary iodine intake was calculated by a food-frequency questionnaire and a food diary. The dietary intake of iodine among nonsupplement users was below the recommendations, whereas the dietary iodine intake of supplement users was above the recommendations. This demonstrates that supplements may contribute considerably to the total dietary iodine intake. 

Dietary iodine intake is in the range of the recommended level among children, and below the recommendation among adolescents and subgroups of pregnant women. 

Normal dietary iodine intake is 150pg/day for adults, as recommended by the WHO (2001). 

Previous studies investigating dietary intake of micronutrients have reported that the dupficate portion technique offers the most accurate estimation. A study comparing dietary assessment methods to measure selenium intake concluded that diet record assessment was not adequate for predicting selenium intakes of individuals, and that duplicate diet analysis remains the recommended measure for research purposes (Duffield and Thomson, 1999). Furthermore, Koutras et al. (1970) state that if iodine intake is to be measured, the best method is the dupficate portion technique. However, the dupficate portion technique is labor intensive and requires a significant amount of subject commitment therefore, its use is usually restricted to small groups and data are usually collected over a short period of time. 

Dietary Supplements As dietary supplements are an important source of iodine in the vegan diet, the accurate assessment of iodine intake from this source is important. The use of dietary supplements by vegans is a crucial factor in determining their iodine intake and assessing whether supplement users could be at risk of excessive intakes of iodine. However, dietary supplements may be a confounding factor in the assessment of iodine intake, as there is uncertainty and variability in their iodine content (Lee et at, 1994). Furthermore, an excessive intake of iodine through some dietary supplements is not difficult because of their concentrated formulation and manufacmrers recommendations about the number of tablets to be taken, which may further exacerbate excessive intake. 

Draper et al. (1993) found that dietary supplements contributed to total iodine intake, providing approximately 11% of the recommended intake. Similarly, Lightowler and Davies (1998) observed that iodine-containing supplements significantly increased iodine intake in vegans, and estimated that such supplements provided, on average, 54 xg iodine per day or 39% of the recommended intake of l40 j,g. 

Although Abdulla et al. (1981) found that the iodine intake in their vegans did not meet the recommended daily amount, the serum levels of T4 and TSH did not indicate any signs of iodine deficiency (Table 45.4). The differing results of low dietary iodine intakes, but adequate biochemical measurements, may be attributed to the length of time the body may take to adapt to a specific diet, as... 

Iodine deficiency during the perinatal period and exposure to an iodine excess is quite conspicuos. The iodine intake of newborns is entirely dependent on the iodine content of breast milk and formula preparations used to feed them. The minimum recommended dietary allowance (RDA) for different age groups is summarized in Table 50.1. To meet such requirements, the iodine content of formulas for premature newborns should contain 20 j,g/dl, and that of first and follow-up preparations 10 j,g/dl. We refer here to these new... 

Fish sauce, Thailand (Chavasit et al., 2003) 15 ml Iodine + iron 50 pg iodine per serve offish sauce, 1/3rd Thai recommended dietary intake per serving (150 meg) ... 

From the review of prior studies on primary hypothyroidism due to Hashimotos thyroiditis and other causes, the success rate of dietary iodine restriction alone without thyroid hormone replacement seems to be approximately 50—80%. Although the ideal cut-off value for dietary iodine restriction for patients with hypothyroidism has not been determined yet, the daily recommended iodide intake of 150p,g for nonpregnant adults by the World Health Organization should be taken into consideration (Table 77.4). It took less than 3 weeks for the dietary iodine restriction to take effect in normafizing thyroid function, and the longer the duration of the dietary restriction, the higher was the response rate observed (54.5% after... 

---