The influence of prenatal and postnatal exposure to dioxins and PCBs on ADHD related behaviour in Norwegian children

Exposure to dioxins and polychlorinated biphenyls (PCBs) during pregnancy and breastfeeding may lead to adverse health effects in children. The aim of this thesis was to study determinants of exposure to dioxins and PCBs during pregnancy and early childhood and examine associations between early life exposure to these compounds and child neurodevelopment. The work was conducted using data from the Norwegian Mother and Child Cohort Study (MoBa), a nationwide population-based pregnancy cohort which follows mothers, fathers and their children from early fetal life and onwards during childhood. Data and material from MoBa and the subcohorts BraMat and The ADHD study were used to assess maternal dietary exposure during pregnancy, blood concentrations in pregnant women and children, as well as neurodevelopmental outcomes in three year old children, including cognitive function and early symptoms related to ADHD. The results indicate that the exposure to dioxins and PCBs was low for most pregnant women and children in MoBa, and that maternal consumption of fish and other commonly consumed foods did not entail daily intakes above established tolerable weekly intakes for dioxins and dioxin-like PCBs. However, consumption of roe liver paté and seagull eggs was related to a particular high dietary exposure, and the results indicate that such high maternal exposure during pregnancy was associated with a small reduction in their children?s language skills at age three years. Notably, no associations were found with a range of other neurodevelopmental measures related to ADHD or cognitive function. Factors related to maternal and child characteristics were taken into account in the analyses. The results in this thesis support the current dietary advice to children and women of childbearing age and show that dietary exposure to dioxins and PCB is reduced by adherence to existing recommendations: avoid seagull eggs and high consumption of fish liver, including roe liver paté.

Attention-deficit/hyperactivity disorder (ADHD) is among the most common chronic disorders among children in Norway and worldwide, with a prevalence of about 3-5%. Children with ADHD are characterised by inattention, impulsivity and hyperactivity, and con sequences of the disorder are substantial both for the individual and his/her surroundings. The present project aims to study the potential influence of exposure to the environmental contaminants dioxins and polychlorinated biphenyls (PCB) on the developm ent of ADHD in children. Dioxins and PCBs are toxic compounds widely spread in soil and sediments due to pollution and frequent use in industrial products during many decades. Adverse effects of dioxins and PCBs on neurodevelopment have been reported in s everal human studies. Likewise, a possible association with ADHD has been described both in animal and human studies. However, no prospective studies of substantial size and with clinically assessed ADHD symptoms as the outcome has to our knowledge been c onducted to investigate these associations. We will use the Norwegian Mother and Child Cohort Study (MoBa) with the ADHD sub-study, to examine the effect of both prenatal and postnatal exposure to the environmental contaminants and their associations with ADHD symptoms in Norwegian children. First, we will estimate levels of exposure to dioxins and PCBs for the children in MoBa. The child is potentially exposed to contaminants through several routes during early development; in utero, through breast milk and through early diet. Secondly, we will include children with clinically significant symptoms of ADHD at 3 years of age in the ADHD sub-study as well as controls from the MoBa cohort and investigate whether exposure to dioxins and PCBs is associated wit h symptoms and signs of ADHD. Knowledge about the aetiology of ADHD is limited and it is of great public health importance, for the purpose of prevention, to identify risk factors for the development of ADHD.