Children who live in the U.S. Northwest's wettest counties are more likely to have autism. When researchers plotted autism rates for children born in California, Oregon and Washington against daily precipitation reports, they found a positive relations to the amount of precipitation in the county where the children were located.
No one know what causes autism, whose symptoms range from severe social avoidance to repetitive behaviors and sometimes profound mental retardation.
Doctors have theorized that something in the environment -- and possibly conditions in the womb -- can trigger the condition. Researchers suggested, based on the new study, that vitamin D deficiency caused by insufficient time in the sun might be a trigger.