A recent study has found a link between the use of vinyl and PVC flooring in homes and the risk of autism.
Recently the focus of autism research has slowly shifted from purely genetic influences to environmental factors and how these interact with genetic traits - perhaps switching on genes which trigger autism (a developing area of science known as 'epigenetics').
Researchers have previously noted a correlation between a mothers exposure to organochlorine pesticides during pregnancy and autism; rates increasing with proximity to agricultural land and amount of pesticide used. Studies have not previously linked anything in a child's environment to their chances of developing autism however.
Now Swedish researchers studying associations between indoor air pollution and allergies may have inadvertently done just that.
In the study parents were asked to complete questionnaires that asked a variety of questions related to the indoor environment. Questions included some focusing on types of flooring. Chemicals called phthlates, which are used to make soft plastics including those in vinyl and PVC flooring, have previously been linked to allergies and asthma
Of the 4,779 children between the ages of 6 and 8 involved in the study, 72 had autism, of which 60 were boys. This gender bias is typical for reasons not yet fully explained.
What the researchers noticed when they analyzed the data was that infants or toddlers who had vinyl or PVC floors in their bedrooms were twice as likely to have autism five years later, in 2005, than those with wood or linoleum flooring.
Professor of environmental medicine at University of Rochester, Bernard Weiss, who co-authored the study, said the connection between these phthalate-containing types of flooring and autism "turned up virtually by accident." He said it was "intriguing and baffling at the same time."
Writing in the journal Neurotoxicology the researchers said "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," they added.
The lead researcher, Carl-Gustav Bornehag of Karlstad University in Sweden, had previously found high rates of asthma and allergies among children living in households with dust containing phthalates. In the Neurotoxicology paper the researchers say they don't know whether allergies and asthma are linked to autism of whether phthalates might cause autism by some other mechanism, if at all. Animal research has shown that phthalates are what are known as 'endocrine-disruptors', chemicals which interfere with the function of hormones in the body. Interestingly, organochlorine pesticides are another example of such chemicals. Phthalates specifically interfere with the male sex hormone testosterone and sexual development.
Three other environmental factors were also associated with autism in the current study: mother's smoking, family economic problems and condensation on windows.
Condensation on windows can be a sign of poor ventilation which could lead to a build up of chemicals such as phthalates and a more toxic indoor environment.
Because this study involves only a small number of children with autism its findings can only be seen as preliminary. The researcher's themselves state this in their paper and suggest larger studies be established to specifically investigate the link between vinyl and PVC flooring, phthalates, and autism.
Larssona M Weiss B Jansona S Sundell J, Bornehag C (2009) Associations between indoor environmental factors and parental-reported autistic spectrum disorders in children 68 years of age Neurotoxicology (online here)
Roberts EM English PB Grether JK Windham GC Somberg L Wolff C (2007) Maternal Residence Near Agricultural Pesticide Applications and Autism Spectrum Disorders among Children in the California Central Valley Environmental Health Perspectives 115(10):1482-9