Objective: To evaluate a food frequency questionnaire (FFQ) used to assess
the dietary intake of iodine.
Design: The iodine intake determined by the FFQ was compared with 4-day die
tary records and with iodine excretion in 24 h urine samples in a subgroup
of participants in a cross-sectional study of iodine intake and thyroid dis
eases in Denmark. Furthermore, the intake of fish determined from the FFQ w
as compared with the intake of fish from a simple record kept for 3 months.
Subjects: Women aged 25-30 y and 60-65 y.
Results: Median iodine intake was similar when determined from the FFQ and
from dietary records and the correlation between these measures was 0.52 (P
< 0.001). Iodine intake was higher than iodine excretion (P < 0.001). The
cross-check questions in the FFQ (for example the question 'How often did y
ou get any kind of fish?') underestimated the intake. In contrast, the inta
ke of a specific fish tended to be overestimated by the FFQ when compared w
ith the 3 month record of fish intake.
Conclusion: The FFQ can be used to classify subjects into low and high iodi
ne intake groups, but the level of iodine tends to be overestimated.
Sponsorship: The Danish Medical Foundation and the 1991 Pharmacy Foundation
.