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Observational Study
. 2017 Nov 13;9(11):1239.
doi: 10.3390/nu9111239.

Maternal Iodine Intake and Offspring Attention-Deficit/Hyperactivity Disorder: Results from a Large Prospective Cohort Study

Marianne Hope Abel  1   2   3 , Eivind Ystrom  4   5   6 , Ida Henriette Caspersen  7 , Helle Margrete Meltzer  8 , Heidi Aase  9 , Liv Elin Torheim  10 , Ragna Bugge Askeland  11 , Ted Reichborn-Kjennerud  12   13 , Anne Lise Brantsæter  14
Affiliations
Observational Study

Maternal Iodine Intake and Offspring Attention-Deficit/Hyperactivity Disorder: Results from a Large Prospective Cohort Study

Marianne Hope Abel et al. Nutrients. .

Abstract

Current knowledge about the relationship between mild to moderately inadequate maternal iodine intake and/or supplemental iodine on child neurodevelopment is sparse. Using information from 77,164 mother-child pairs in the Norwegian Mother and Child Cohort Study, this study explored associations between maternal iodine intake and child attention-deficit/hyperactivity disorder (ADHD) diagnosis, registered in the Norwegian Patient Registry and maternally-reported child ADHD symptoms at eight years of age. Pregnant women reported food and supplement intakes by questionnaire in gestational week 22. In total, 1725 children (2.2%) were diagnosed with ADHD. In non-users of supplemental iodine (53,360 mothers), we found no association between iodine intake from food and risk of child ADHD diagnosis (p = 0.89), while low iodine from food (<200 µg/day) was associated with higher child ADHD symptom scores (adjusted difference in score up to 0.08 standard deviation (SD), p < 0.001, n = 19,086). In the total sample, we found no evidence of beneficial effects of maternal use of iodine-containing supplements (n = 23,804) on child ADHD diagnosis or symptom score. Initiation of iodine supplement use in gestational weeks 0-12 was associated with an increased risk of child ADHD (both measures). In conclusion, insufficient maternal iodine intake was associated with increased child ADHD symptom scores at eight years of age, but not with ADHD diagnosis. No reduction of risk was associated with maternal iodine supplement use.

Keywords: ADHD; MoBa; Norwegian Patient Registry; Norwegian mother and child cohort study; attention-deficit/hyperactivity disorder; dietary supplements; iodine; neurodevelopment; pregnancy.

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Conflict of interest statement

The first author of this paper is employed by a Norwegian dairy company (TINE SA), and she participates in this project as an industrial PhD-student financed partly by the dairy company and partly by The Research Council of Norway. This project is designed, owned and administered by The Norwegian Institute of Public Health and analysis of the data follow from protocol. All results of analysis in the project are to be published regardless of the results. The dairy company supports the study to raise awareness on the importance of iodine and to gain more knowledge about the potential health effects of milk in the Norwegian diet. Apart from the PhD-student, no one from the dairy company has been involved in the study, and in itself, the company had no direct influence on the analysis and interpretation of the results. The other authors had no conflicts of interest.

Figures

Figure 1
Figure 1
Flow-chart of inclusion. 1 Questionnaire 1 was answered around gestational week 17. 2 The FFQ (questionnaire 2) used in the present study was included in The Norwegian Mother and Child Cohort Study (MoBa) from 2002 and was answered around gestational week 22. FFQ: Food frequency questionnaire, BMI: Body Mass Index, ADHD: attention-deficit/hyperactivity disorder.
Figure 2
Figure 2
Association between maternal iodine intake from food and proportional risk of child ADHD diagnosis. Results are from multivariable regression analysis and are restricted to non-users of iodine supplements during first half of pregnancy (n = 53,360 mother–child pairs). Iodine intake was modelled by restricted cubic splines (four knots), and the reference level was set to 160 µg/day. Dashed lines represent 95% confidence limits. The histogram (b) illustrates the distribution of iodine intake. Both models (a,b) were adjusted for random effects of sibling clusters and for energy intake to control for measurement error. The adjusted model (b) was additionally adjusted for maternal age, BMI, parity, education, smoking in pregnancy, and fiber intake. The vertical axis on hazard ratios are on the log scale. ADHD: attention-deficit/hyperactivity disorder.
Figure 2
Figure 2
Association between maternal iodine intake from food and proportional risk of child ADHD diagnosis. Results are from multivariable regression analysis and are restricted to non-users of iodine supplements during first half of pregnancy (n = 53,360 mother–child pairs). Iodine intake was modelled by restricted cubic splines (four knots), and the reference level was set to 160 µg/day. Dashed lines represent 95% confidence limits. The histogram (b) illustrates the distribution of iodine intake. Both models (a,b) were adjusted for random effects of sibling clusters and for energy intake to control for measurement error. The adjusted model (b) was additionally adjusted for maternal age, BMI, parity, education, smoking in pregnancy, and fiber intake. The vertical axis on hazard ratios are on the log scale. ADHD: attention-deficit/hyperactivity disorder.
Figure 3
Figure 3
Association between maternal iodine intake from food and standardized score on maternally reported child ADHD symptoms at age eight years. Results are from multivariable regression analysis and restricted to non-users of iodine supplements during the first half of pregnancy (n = 19,086 mother-child pairs). Iodine intake was modelled by restricted cubic splines (four knots), and the reference level was set to 160 µg/day. Dashed lines represent 95% confidence limits. The histograms (e,f) illustrate the distribution of iodine intake. Crude models (a,c,e) were adjusted for maternal energy intake and for random effects of sibling clusters. Adjusted models (b,d,f) were additionally adjusted for maternal age, parity, education, body mass index, smoking in pregnancy, fiber intake, child sex, and birth season.
Figure 3
Figure 3
Association between maternal iodine intake from food and standardized score on maternally reported child ADHD symptoms at age eight years. Results are from multivariable regression analysis and restricted to non-users of iodine supplements during the first half of pregnancy (n = 19,086 mother-child pairs). Iodine intake was modelled by restricted cubic splines (four knots), and the reference level was set to 160 µg/day. Dashed lines represent 95% confidence limits. The histograms (e,f) illustrate the distribution of iodine intake. Crude models (a,c,e) were adjusted for maternal energy intake and for random effects of sibling clusters. Adjusted models (b,d,f) were additionally adjusted for maternal age, parity, education, body mass index, smoking in pregnancy, fiber intake, child sex, and birth season.
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