Elsevier

NeuroToxicology

Volume 30, Issue 5, September 2009, Pages 822-831
NeuroToxicology

Associations between indoor environmental factors and parental-reported autistic spectrum disorders in children 6–8 years of age

https://doi.org/10.1016/j.neuro.2009.01.011Get rights and content

Abstract

Potential contributions of environmental chemicals and conditions to the etiology of Autism Spectrum Disorders are the subject of considerable current research and speculation. The present paper describes the results of a study undertaken as part of a larger project devoted to the connection between properties of the indoor environment and asthma and allergy in young Swedish children. The larger project, The Dampness in Buildings and Health (DBH) Study, began in the year 2000 with a questionnaire distributed to parents of all children 1–6 years of age in one Swedish county (DBH-I). A second, follow-up questionnaire (DBH-III) was distributed in 2005. The original survey collected information about the child, the family situation, practices such as smoking, allergic symptoms, type of residence, moisture-related problems, and type of flooring material, which included polyvinyl chloride (PVC). The 2005 survey, based on the same children, now 6–8 years of age, also asked if, during the intervening period, the child had been diagnosed with Autism, Asperger's syndrome, or Tourette's syndrome. From a total of 4779 eligible children, 72 (60 boys, 12 girls) were identified with parentally reported autism spectrum disorder. A random sample of 10 such families confirmed that the diagnoses had been made by medical professionals, in accordance with the Swedish system for monitoring children's health. An analysis of the associations between indoor environmental variables in 2000 as well as other background factors and the ASD diagnosis indicated five statistically significant variables: (1) maternal smoking; (2) male sex; (3) economic problems in the family; (4) condensation on windows, a proxy for low ventilation rate in the home; (5) PVC flooring, especially in the parents’ bedroom. In addition, airway symptoms of wheezing and physician-diagnosed asthma in the baseline investigation (2000) were associated with ASD 5 years later. Results from the second phase of the DBH-study (DBH-II) indicate PVC flooring to be one important source of airborne phthalates indoors, and that asthma and allergy prevalence are associated with phthalate concentrations in settled dust in the children's bedroom. Because these associations are among the few linking ASD with environmental variables, they warrant further and more extensive exploration.

Introduction

Over the past few decades, our understanding of the genesis and character of autism has undergone a series of transformations. It is now viewed, not as a unitary disorder, but as one with multiple dimensions (hence the term, autism spectrum disorder, ASD), displaying many degrees of severity, and attributable to a variety of potential causes. We now recognize that its manifestations touch many organ systems as well as the brain. We still view it as rooted in genetics, but subject as well to environmental events and circumstances. Exposures to aberrant environmental conditions and to chemical contaminants, in particular, are now seen as possible factors in its etiology.

The current report emphasizes one class of conditions and contaminants; in essence, those arising from the indoor environment, which could be relevant from an exposure point of view since we spend most of our time in such environments. The report is one of a series directed originally at how certain properties of the indoor environment such as moisture-related problems and different building materials are associated with allergies and asthma in Swedish children. Almost adventitiously, the investigation uncovered an apparent association between certain of these properties and medically diagnosed ASD. The data are far from conclusive. They are puzzling, even baffling, and not readily explicable at this time. However, because they are among the few clues that have emerged about possible environmental contributions to autistic disorders, we believe that they should be weighed carefully and warrant further study.

The global incidence of allergy and asthma has risen substantially over the past three decades (Beasley, 2002, Beggs and Bambrick, 2005), as it has in Swedish children. One possible factor contributing to this rise, noted repeatedly in the literature, is the character of the indoor environment and exposures occurring in that setting. Because moisture-related problems or “dampness” have been associated with respiratory symptoms and with allergy and asthma in numerous studies (reviewed in Bornehag et al., 2005b) a consortium of Swedish organizations and institutions undertook an epidemiological study designated the “Dampness in Buildings and Health” study (DBH). DBH began in 2000. Its central aim is to determine elements of the indoor environment associated with asthma and allergic symptoms among small children and their parents. The choice of young children as the study population arose from two considerations. First, preschool children display a higher incidence of allergies than adults. Second, most of their time is spent in the home, the environment that is the focus of the effort. Children are also more vulnerable due to a relatively higher intake of food and a higher breathing frequency.

The data reported here represent one set of DBH findings. They describe associations between ASD in children aged 6–8 years and a number of environmental factors, including exposure conditions when they were 1–3 years of age and, almost surely, during pregnancy and the first year of life.

Section snippets

Method

The Dampness in Buildings and Health (DBH) study has so far embodied three phases.

  • DBH-I, a cross-sectional study based on a questionnaire sent to parents of 14,077 children in the county of Värmland in 2000 (Bornehag et al., 2004a).

  • DBH-II, a nested case–control study of 198 symptomatic children and 202 healthy controls from DBH-I (Bornehag et al., 2004b).

  • DBH-III, a 5-year follow-up study of those eligible for DBH-I, conducted in 2005.

The data in the current paper are based on the initial

Results

Of the 4779 children in the study, 50% were girls (n = 2391) and age was evenly distributed among the participants (Table 1). A variety of changes occurred in family conditions and circumstances between 2000 and 2005. In 2000, 81% of the families lived in a single-family house; 5 years later this figure had increased to 86%. The proportion of homes larger than 150 square meters increased from about 21% to 28%. The most common type of flooring in the child's and the parent's bedroom in 2000 was

Discussion

At this time, we lack any firm knowledge about the extent to which environmental chemicals or other environmental conditions might influence the etiology or manifestations of ASDs. That is, using the terminology of cancer risk assessment, do they act primarily as initiators, or primary causes, or are they more like promotors, simply enhancing or amplifying a process already underway, or is it just a matter of confounding? For other neurodevelopmental endpoints, the past few decades have

Implications and conclusions

Our findings, and the questions they evoke, may be listed as follows:

  • Phthalate exposure early in development appears linked to ASD.

    Is the link due to its association with allergies and asthma? Is it an independent factor, acting perhaps via endocrine disruption? Or is it a confounding phenomenon not yet identified? Biomarkers such as urinary metabolites would be a useful source of answers.

  • Other indoor environmental variables such as dampness, are also linked to ASD.

  • Is ventilation rate in the

Conflict of interest statement

None.

Acknowledgements

The study was funded by grants from the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (Formas), Swedish Asthma and Allergy Association's Research Foundation, and the Swedish Foundation for Health Care Sciences and Allergy Research. The participation of B. Weiss was supported in part by NIEHS grants ES013247 and ES015509 and Center grant ES01247.

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