Circadian rhythms in urinary trace element and electrolyte excretion in children with and without endemic goiter

Six boys and six girls 11 +/- 1.5 years of age living in the endemic goiter area of Tîrgovişte, Romania were studied. Three of the children of each sex did have a palpable endemic goiter, three did not. The children followed a diurnal activity pattern synchronized by their school routine and ate their usual three meal diet. Urine was collected at 4-hour intervals over a 24 hour span (six samples). Urinary volume, pH, total (T) solids, protein, glucose, phosphorus, uric acid, urea nitrogen, creatinine, total and nondialyzable (ND) sodium and potassium were determined by conventional methods and the total and nondialyzable (ND) portion of urinary calcium, magnesium, and zinc and the ND portion of aluminum, copper, boron, lead and silicon were determined by an inductively coupled plasma (ICP) system.