Circadian and seasonal variations in iodine excretion in children with and without endemic goiter.

The urinary iodine excretion was measured in 193 children 11 +/- 1.5 years of age living in the endemic goiter area of Dîmboviţa, Romania. One hundred and thirty four of the children showed some degree of endemic goiter, 59 showed none. All children followed a diurnal activity pattern with rest during the night. They received their usual iodine supplement of 1 gm potassium iodide once a week during the school year (which included the time of all measurements made). Urine was collected in six 4-hour samples over a 24-hour span. The examinations were conducted during the months of March, June, September and December. Iodine was determined by an automated ceric ion arsenic acid method using a Technicon Autoanalyzer. Circadian and seasonal variations of urine volume and iodine excretion were statistically verified by the cosinor technique and the seasonal variations also by one way analysis of variance using the circadian means as input. A comparable circadian rhythm of iodine excretion was found in the children with and without endemic goiter, with an acrophase during the evening (20:16 with a 95% C.I., from 19:32 to 21:04). The circadian rhythm in iodine excretion has to be taken into account whenever an estimate of the 24-hour excretion is attempted from a sample covering less than the entire 24-hour span. There was a statistically significant seasonal variation of the 24-hour iodine excretion in the boys with and without endemic goiter and in the group as a whole. The 24-hour iodine excretion during March was 102 +/- 6 mcg, during June 81 +/- 4 mcg, during September 79 +/- 3 mcg and during December 102 +/- 7 mcg. The average 24-hour iodine excretion pooled over all seasons was 91 +/- 3 mcg/24 hrs in the children with and 91 +/- 5 mcg/24 hrs in the children without endemic goiter. During March and December the iodine excretion indicates an iodine intake not usually associated with a high prevalence of endemic goiter. However, during the months of June and September (and presumably even more during the months of July and August when during summer vacation no iodine supplementation was given in school) the 24-hour iodine excretion indicates some degree of iodine deficiency. The seasonal variation in urinary iodine excretion thus points to a time when increased iodine prophylaxis may be of value.