Background:

Iodine intake is required for thyroid hormone production, which is essential for neurological development. A large proportion of UK women of childbearing age are likely to have insufficient iodine intake, and should they become pregnant, there would be a risk to fetal neurodevelopment. However, there are no useful biomarkers to measure iodine status in an individual; urinary iodine concentration can only be used for population assessment. The aim of this study was therefore to validate an iodine intake screening tool that had previously been developed, against a reference measure for estimating iodine intake. We hypothesized that the short screening tool (28 questions) would be able to correctly classify daily iodine intake as low (˂140 lg), adequate (140 lg - 600 lg) or excessive (˃600 lg).

Methods:

Healthy females aged 18–50 years, were recruited from the University of Surrey population and contacts of the researchers. They were asked to complete the iodine screening tool and a 4-day dietary record using estimated measures of intake. The screening tool was coded to calculate daily iodine intake based on estimated iodine content per portion and frequency of consumption. Dietary records were analysed in Nutritics to give an average daily iodine intake. Values from the tool and the dietary record were compared using a Spearman Rank correlation and Bland-Altman analysis. Cohen's j was used to assess iodine intake classification from the two methods of assessment. A sensitivity analysis was performed to exclude outliers and highlight variations in individual components of the screening tool. The project received a favourable ethical opinion from the Faculty of Health and Medical Sciences Ethics Committee (University of Surrey).

Results:

Twenty-one female participants (mean age 33 ± 4) were recruited. There was no significant difference (p = 0.566) between median iodine intake from the screening tool (155 lg/day, interquartile range (IQR): 70–180 lg) and dietary records (100 lg/day, IQR: 88–176 lg). There was a moderate correlation (rs=0.540, p = 0.012) and moderate agreement for categorisation of participants based on iodine intake (j=0.521, p = 0.017) with 67% of those with low intakes according to the reference measure also being categorized as low using the screening tool (Table 1); none of the participants had excessive iodine intake. The exclusion of brown seaweed improved sensitivity of the tool (to 75%) by removing outliers. Bland- Altman analysis indicated high accuracy but large limits of agreement.

Discussion:

The percentage of women correctly classified was similar or higher than other validation studies of food frequency questionnaires (FFQs) using dietary records as a reference measure (45% - 66%)1–3. The Cohen’s j value is also higher than those from those studies (0·15 - 0·3), indicating a greater agreement regarding classification.

Conclusion:

The screening tool is a quick, simple and moderately accurate method of classifying individuals into low and normal intakes of iodine using 4-day dietary records as a reference measure.