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Smyth
Iodine uptake and loss-can frequent strenuous exercise induce iodine deficiency?
Smyth PP, Duntas LH.
Horm Metab Res. 2005 Sep;37(9):555-8. Review.
[abstract only]
"Most of the daily
dietary iodine intake (approximately 90 %) will be excreted in
the urine; measurement of urinary iodine excretion is thus
routinely used as an index of dietary iodine intake. However,
urinary excretion is not the only means of iodine loss. Subjects
such as athletes or those participating in vigorous exercise can
lose a considerable amount of iodine in sweat, depending on
environmental factors such as temperature and humidity. In areas
of lower to moderate dietary iodine intake, loss in sweat can
equal that in urine. Although electrolyte loss in sweat is
well-recognized and replacement strategies are adopted, there is
less recognition of potential iodine loss. Crude calculations
reveal that if sweat iodide losses are not replaced, dietary
stores could be depleted in an athlete undergoing a regular
training regime. The significance of these losses could be
increased in areas where dietary iodine intake is lower in the
summer months. Although there is little doubt that excessive
sweating can induce a relative iodine deficiency state, there is
no case as yet for iodine supplementation in those that take
vigorous exercise. However, sustained iodine loss may have
implications for thyroid status and possibly consequences for
athletic performance."
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