Condition category
Mental and Behavioural Disorders
Date applied
Date assigned
Last edited
Retrospectively registered
Overall trial status
Recruitment status
No longer recruiting
Publication status

Plain English Summary

Background and study aims
A lack of certain nutrients (deficiency) during critical phases in brain development may result in irreversible functional changes to the brain, the most critical period being pregnancy (gestation) and the early years of life. There is evidence for a link between low iodine levels during pregnancy and later attention-deficit/hyperactivity disorder (ADHD) in the child, but more studies are needed. Studies are also needed to explore whether iodine supplements in pregnancy can compensate for a lack of iodine in the diet. The WHO currently recommends the use of iodine supplements in pregnancy in areas where pregnant women are at risk of mild- to moderate iodine deficiency, but the recommendation lacks scientific support. Some studies even indicate that starting iodine supplementation in pregnancy might have negative effects. It is very important to clarify these relationships as soon as possible in order to design preventive strategies. The main aim of this study is to examine the possible link between iodine intake from food in pregnancy and the risk of ADHD in the child at age 8 years. A second aim is to explore the links between use of iodine-containing supplements before and during pregnancy and the risk of ADHD.

Who can participate?
Pregnant women in their first trimester recruited from all over Norway during the years 1999 to 2008

What does the study involve?
Participants’ iodine intake from food and use of iodine-containing supplements are assessed using questionnaires. ADHD symptoms of the children at age 8 years are assessed by questionnaire, and ADHD diagnoses are obtained from the Norwegian Patient Registry.

What are the possible benefits and risks of participating?
As this is an observational study there are no benefits or risks for the individual participants, but there is a potential large benefit for society and for future generations. The results from this study are communicated to participants through the study website and by newsletters to all participating families.

Where is the study run from?
Norwegian Institute of Public Health (Norway)

When is the study starting and how long is it expected to run for?
August 2016 to December 2017

Who is funding the study?
1. Norwegian Ministry of Health (Norway)
2. Norwegian Ministry of Education and Research (Norway)
3. National Institute of Environmental Health Sciences (USA)
4. National Institute of Neurological Disorders and Stroke (USA)

Who is the main contact?
Dr Anne-Lise Brantsaeter

Trial website

Contact information



Primary contact

Dr Anne Lise Brantsaeter


Contact details

Department of Exposure and Environmental Epidemiology
Division of Infection Control and Environmental Health
Norwegian Institute of Public Health
PO Box 4404 Nydalen

Additional identifiers

EudraCT number number

Protocol/serial number


Study information

Scientific title

Maternal iodine intake and offspring attention deficit-hyperactivity disorder


Study hypothesis

The main aim of the current study was to explore the association between iodine intake from food in pregnancy (as a proxy for long-term iodine intake and status) and i) risk of specialist-diagnosed ADHD in the child and ii) maternal report of child ADHD symptoms at age 8 years. A second aim was to explore the associations between maternal use of iodine-containing supplements prior to and during pregnancy and the same outcome measures.

Ethics approval

The Regional Committee for Medical Research Ethics South East Norway, 20/10/2016, ref: REK 2013/594

Study design

Observational population-based prospective pregnancy cohort

Primary study design


Secondary study design

Epidemiological study

Trial setting


Trial type


Patient information sheet

Not available in web format, please use the contact details to request a patient information sheet


Child ADHD diagnosis and maternally reported child ADHD symptoms at age 8 years


1. Maternal iodine intake from food in non-users of supplemental iodine assessed by a food frequency questionnaire in gestational week 22
2. Maternal use of iodine-containing supplements (dosage and time of initiation) assessed by questionnaires in pregnancy (gestational week 17 and 22)

Intervention type



Drug names

Primary outcome measure

1. Registered child ADHD diagnosis in the Norwegian Patient Registry (NPR) by Dec. 2015. From 2008, all government-owned and government-financed hospitals and outpatient clinics mandatorily report individual level diagnoses defined in the tenth revision of the International Classification of Disease (ICD-10) to the NPR in order to receive financial reimbursement. Using individual personal identification numbers, diagnostic information from NPR was linked to MoBa. Thus all MoBa children registered with an ICD-10-diagnosis of hyperkinetic disorder (HKD coded as F90.0, F90.1, F90.8, or F90.9) between 2008 and 2015 were identified and regarded as having ADHD
2. Child ADHD symptoms assessed in the 8 year questionnaire from MoBa on a 4-point Likert scale (never/rarely, sometimes, often, or very often) covering inattention problems (9 items) and hyperactivity/impulsivity (9 items) from the ADHD Rating Scale

Secondary outcome measures

No secondary outcome measures

Overall trial start date


Overall trial end date


Reason abandoned (if study stopped)


Participant inclusion criteria

1. Pregnant women in their first trimester recruited from all over Norway during the years 1999 to 2008 and asked to answer questionnaires (in Norwegian) at regular intervals during pregnancy and after birth
2. To be included in the current study mothers had to have responded to a general questionnaire around gestational week (GW) 17, and a food frequency questionnaire (FFQ) around GW 22
3. Only singleton pregnancies
4. Only participants with information on all covariates were included in the analysis because of the large sample size and low rates of missing values
5. Pregnant women at any age were allowed to participate

Participant type


Age group




Target number of participants

A total of 77,164 mother-child pairs were included in this study, and for 27,945 there were data on maternally reported ADHD score at child age 8 years

Participant exclusion criteria

1. Multiple pregnancies
2. Maternal use of thyroid medication in pregnancy
3. Missing information on important covariates
4. Children registered as dead or emigrated by Jan 2016
5. FFQs with more than 3 blank pages
6. Calculated energy intakes <4.5 MJ or >20 MJ

Recruitment start date


Recruitment end date



Countries of recruitment


Trial participating centre

Norwegian Institute of Public Health
PO Box 4404 Nydalen

Sponsor information


The Norwegian Research Council

Sponsor details

Postboks 564
+47 (0)22037000

Sponsor type

Research council




Sponsor details

Postboks 25

Sponsor type




The Research Council of Norway

Sponsor details

Sponsor type




Funder type


Funder name

Norwegian Ministry of Health

Alternative name(s)

Funding Body Type

Funding Body Subtype


Funder name

Norwegian Ministry of Education and Research

Alternative name(s)

Funding Body Type

Funding Body Subtype


Funder name

National Institute of Environmental Health Sciences (contract no N01-ES-75558)

Alternative name(s)


Funding Body Type


Funding Body Subtype


Funder name

National Institute of Neurological Disorders and Stroke (grant no.1 UO1 NS 047537-01 and grant no.2 UO1 NS 047537-06A1)

Alternative name(s)

Funding Body Type

Funding Body Subtype


Results and Publications

Publication and dissemination plan

This study will result in one publication in an international peer-reviewed journal.

IPD sharing statement
No data can be shared because of data protection regulations. Other researchers, nationally and internationally, will have access to the cohort on request. For more information about research and data access from the Norwegian Mother and Child Cohort Study see:

Intention to publish date


Participant level data

Not expected to be available

Basic results (scientific)

Publication list

2017 results in:

Publication citations

Additional files

Editorial Notes

03/08/2018: Publication reference added.