Validation and reproducibility of a new iodine specific food frequency questionnaire for assessing iodine intake in Norwegian pregnant women

Table 2 Descriptive of estimated iodine intake from the I-FFQ and food diary (μg/day), and urinary iodine concentration (UIC, μg/L) and estimated iodine intake from UIC (μg/day) in pregnant women (gestational week 18-19) enrolled in the Mommy’s Food study

	N	Mean (SD) ^f	Median (p25-p75)	p5-p95
Estimated iodine intake, I-FFQ, μg/day ^a
Diet	124	134 (73)	123 (89–157)	51, 309
Diet and supplements	124	202 (108)	202 (106–275)	60, 377
Estimated iodine intake, food diary, μg/day ^b
Diet	134	116 (51)	105 (80–153)	42, 203
Diet and supplements	134	171 (99)	151 (87–262)	47, 342
Urinary iodine concentration (UIC), μg/L ^c
All participants	134	103 (56)	94 (62–130)	36, 210
Non-supplement users ^d	87	89 (49)	77 (58–120)	31, 172
Supplements users ^d	47	129 (58)	130 (77–160)	49–270
Estimated iodine intake from UIC, μg/day ^e
All participants	117	166 (93)	147 (104–206)	61, 404
Non-supplement users ^d	75	135 (69)	119 (83–169)	46, 273
Supplement users ^d	42	220 (105)	202 (143–262)	73, 439

^a Iodine specific food frequency questionnaire (I-FFQ)
^b Iodine specific food diary from six consecutive days
^c Pooled sample of spot urinary samples from six consecutive days
^d Reported use of iodine containing supplement in the food diary
^e Estimated from the equation: Urinary iodine concentration (μg/L) × 0.0235 × body weight (kg) (IOM 2001) [28]. Self-reported current body weight used for estimation (data of n = 17 missing)
^f Differences between the different methods were tested by Wilcoxon’s signed-rank test. Difference between estimated iodine intake from I-FFQ and food diary (without supplements): P = 0.030; estimated iodine intake from I-FFQ and food diary (with supplements): P = 0.002; estimated iodine intake from UIC and food diary: P = 0.882; estimated iodine intake from UIC and I-FFQ: P = 0.001

ISSN: 1475-2891