In The Politics of Autism, I discuss various ideas about what causes the condition. Here is just a partial list of correlates, risk factors, and possible causes that have been the subject of serious studies:
- Air pollution and proximity to freeways;
- Maternal thyroid issues;
- Autoimmune disorders;
- Induced labor;
- Preterm birth;
- Birth by cesarean section;
- Maternal and paternal obesity;
- Maternal diabetes;
- Maternal and paternal age;
- Maternal post-traumatic stress disorder;
- Smoking during pregnancy;
- Antidepressant use during pregnancy;
- Polycystic ovary symdrome.
Mothers with high levels of the pesticide DDT in their blood during pregnancy are more likely to bear children who develop autism, according to a study of blood samples from more than one million pregnant women in Finland.
The World Health Organization estimates that globally, one in 160 children has autism. Any case of autism is likely due to a number of factors, including genetics and other environmental exposures.
Although the authors stress that the findings do not prove that autism is caused by DDT — whose use has been banned in many countries for decades over concerns about its effects on wildlife— it is the first such association using a direct measure of exposure to the pesticide. Researchers who investigate links between environment and disease say that further studies are needed to determine the mechanism, if any, by which DDT exposure could trigger autism.
The study, published on 16 August in the American Journal of Psychiatry, also examined mothers’ exposure to another set of chemicals known as polychlorinated biphenyls (PCBs), and found no association between these substances and autism. That finding deepens questions about whether or how DDT might be linked to autism.