A food frequency questionnaire (FFQ) covering iodine-rich foods
was given to all participants in both studies when they arrived at
the centers.
The FFQ was semi-quantitative and was similar in both
studies, except that ten questions on bread intake were added to
the questionnaire in C1b because of the iodine fortification of bread
salt. So the FFQ referred to a list offifty-three iodine-rich food items
in C1a and sixty-three in C1b.
The FFQ has been evaluated and described in more detail. Iodine intake was calculated for 4347 participants in C1a and for 2424 in C1b.