2.4. Urine collections
All participants were asked to give a urine sample when they
visited the centers between 08.00 a.m. and 5.30 p.m. These spot
urine samples were analyzed for iodine and creatinine. Iodine
excretion was expressed in two ways: as a concentration and as an
estimated 24-h urinary iodine excretion. To calculate the estimated
24-h urinary iodine excretion, the iodine/creatinine ratio was
multiplied by the calculated 24-h creatinine excretion. The calculation
of the 24-h creatinine excretion was done by using the
formula: 7.54 age (years) þ 14.15 weight (kg) þ 3.48 height
(cm) þ 423.15 for men and 6.13 age (years) þ 9.97 weight
(kg) þ 2.45 height (cm) þ 342.73 for women. This formula was
developed for a Danish population.9 Iodine concentration in urine
was available for 4616 participants in C1a and 2453 in C1b.