In the scientific hunt for the causes of autism, researchers at UC Davis may have just picked up a new trail: obesity during pregnancy.
Their study, published today in the journal Pediatrics, found obese mothers were 70 percent more likely to have a child with autism and twice as likely to have a child with other kinds of developmental delays compared with normal-weight moms with normal blood pressure and no diabetes.
"That's totally new," said researcher Irva Hertz-Picciotto, professor of epidemiology and chief of environmental and occupational health at the UC Davis MIND Institute. "Nobody has looked at obesity in relation to autism spectrum disorders that I'm aware of."
With obesity rocketing skyward in the United States, the findings "raise serious public health concerns," the authors wrote. However, the results could also represent a step toward uncovering causes of autism and a pathway for further research.
"Currently we really know very little about the causes of autism," Hertz-Picciotto said. "We have a few clues."
Nearly 60 percent of women of childbearing age are overweight, and one-third are obese, the researchers reported. Nearly 9 percent have diabetes.
The study, which involved more than 1,000 children from California, also confirmed earlier findings that a mother's diabetes may play a role in cognitive disabilities in her children.
Diabetic moms were more than twice as likely to have a child with developmental delays other than autism, compared with non-diabetic moms with normal weight and blood pressure. The diabetic moms showed a higher risk of having an autistic child, but the difference wasn't robust enough for scientists to consider it reliable.
Whether they were autistic or not, kids whose moms had diabetes scored lower on language tests than those with non-diabetic moms. That held true even for children who seemed otherwise mentally normal.
Obesity, diabetes and high blood pressure are all implicated in problems with metabolism, the body's processing of food into energy. These metabolic conditions often come together.
So the researchers looked at all three conditions and found that having any one of those significantly increased a mom's risk of having an autistic child though obesity was the strongest factor.
"It's all about the obesity," as it relates to full-fledged autism in these findings, said Michael Greene, director of obstetrics at Massachusetts General Hospital, who was not involved in the study.
"Is diabetes the mechanism that caused the autism spectrum disorder, or is it an innocent bystander (and oh, by the way, it's common in women with obesity)?" Greene asked. Scientists will need more data to answer that question and ferret out the disorder's cause, he said.
"Obesity has been rising and autism has been rising, and people might think, 'Are they linked?' " Hertz-Picciotto said. It could be that one causes the other, or that something else causes them both.
If a mom's obesity does turn out to be causal, the likely trigger for autism could be the chronic inflammation that obesity causes in various systems in the body, Greene said. The UC Davis researchers suggested possible triggers could also be low oxygen levels or lasting exposure to high blood sugar while a fetus is in the womb.
"We see pregnancy as a critical time window," Hertz-Picciotto said. "The brain is going through growth, it's got cells that need to migrate to the right place and connect with other cells. All those things are very delicately timed and require the right amount of energy, and everything else about the intrauterine environment has to be just right."
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