Experts try to pinpoint environmental links to the brain disorder's recent steep climb.
An estimated 1 in 70 boys and 1 in 315 girls in the U.S. now have an autism spectrum disorder (ASD), according to a 2009 study by the Centers for Disease Control and Prevention. Increased awareness and detection as well as earlier diagnoses cannot alone account for the steep increase over the past few decades, experts say.
Autism is now widely believed to be caused by a combination of genetics and environmental factors. "Research indicates that even low-dose environmental exposures during pregnancy and early childhood have an effect on the developing brain," said Linda S. Birnbaum, Ph.D., director of the National Institute of Environmental and Health Sciences, at a congressional hearing last August.
The bodies of young children and fetuses are less able than those of adults to detoxify harmful substances and repair damage, and fetal exposure is of utmost concern, explains Santa Monica, Calif., pediatrician Harvey Karp, M.D. "The brain quadruples in size during the last trimester," he says. "There are windows of vulnerability during this time where even miniscule amounts of chemicals could disturb development."
Pinpointing possible culprits Studies have repeatedly ruled out vaccines as a cause of autism. Currently, indoor and outdoor air pollution, endocrine-disrupting chemicals such as bisphenol-A (BPA) and PBDEs, smoking, alcohol use, medications and infections are being investigated. Already, a 2010 study at the University of Southern California found that children of women who lived within 1,000 feet of a freeway during the third trimester were more than twice as likely to have autism. And research from Columbia University's Mailman School of Public Health in New York found that babies with higher concentrations of the pesticide chlorpyriphos or PBDEs in their umbilical cord blood experience developmental delays later.
The biggest steps to protect children need to be taken federally, says Bruce P. Lanphear, M.D., M.P.H., senior scientist at the Child & Family Research Institute and professor of health sciences at Simon Fraser University in Vancouver, British Columbia. "Currently, each chemical has to individually be proven toxic in animal and human studies before it's regulated," he explains. "Eventually, we should require companies to prove their products are safe." "
For now, pregnant women should try to avoid chemical exposure just like they do alcohol exposure," Karp says. He and Lanphear offer some suggestions:
■ Avoid pesticides, tobacco smoke, plastics and scented products, including candles, incense, air fresheners and personal-care products containing the ingredient "fragrance."
■ Buy organic products and foods when possible, especially those that typically have high pesticide levels, and wash all fruits and vegetables thoroughly.
■ Avoid eating mercury-containing fish, such as tuna and swordfish.
■ Do not eat blackened or charred food, and use a kitchen fan while cooking.
■ Try to avoid living close to a highway.
■ Minimize handling of slippery paper receipts; they can have high BPA levels. A massive effort to examine the effects of the environment on children's health is getting under way; to learn more, including how to participate (it is recruiting pregnant women now), visit nationalchildrensstudy.gov.