Requirement And Recommended Dietary Intakes

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Goiter occurs when iodine intakes are less than about 50 |g/day, and cretinism when intakes of mothers are 30 |g/day or less.12 Minimum requirements to prevent goiter are based on the urinary excretion associated with a high incidence of goiter in a population, estimated at 50 |g/g creatinine, and the observation that a minimum intake of 70 |g/day appears to be necessary to avoid signs of goiter. Therefore, the minimum requirement for prevention of goiter is approximately one |g/kg body weight/day.61 However, recommended dietary intakes are based on physiological requirements, which are in turn based on a number of indicators, including thyroidal radio-iodine accumulation and turnover, iodine balance studies, urinary iodide excretion, thyroid hormones measures and thyroid volume. Physiological requirement is at least equal to the daily amount of hormonal iodine degraded in the peripheral tissues and not recovered by the thyroid. There is an obligatory loss of iodine from the body via urine, feces, and sweat. Fecal iodine loss is relatively constant and is likely to be significant only when iodine intake is very low. Sweat has generally not been considered an important avenue for iodine loss,62 however, losses may be appreciable in hot climates. Urine, the major excretion pathway for iodine, is related to dietary intake. Individuals over a period of time adapt well to low or high iodine intakes, although the length of this adaptation time is uncertain.63 The consensus of reviewed studies would appear to be that iodine balance is achievable at intakes over 100 |g/day and not achievable below 40 |g/day.64 From this physiological requirement of around 100 | g/day, a rather large safety margin is added to give a recommended dietary intake, which for most countries is 150 |g/day.65 This level is adequate to maintain normal thyroid function, which is essential for growth and development. Requirements may increase if the diets contain goitrogens.

At present, there are no recommendations for iodine intake for athletes. However, reports of high sweat losses during strenuous activity22-24 in the heat suggest that further investigation of requirements for active individuals should be made.

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