They're also much less likely to smoke and drink alcohol, a paradoxical finding since those habits can contribute to many conditions that disproportionately affect autistic adults. Scientists say that could mean that their biologic makeup contributes to some of the illnesses.
The study is one of the largest, most comprehensive efforts to examine the health of autistic adults and highlights a need for better strategies to treat them, said scientist Lisa Croen, the lead author and director of the autism research program at Kaiser Permanente Division of Research in Oakland, California.
Some of the same health disparities also have been found in autistic children, but there's little research on whether they persist into adulthood or if new ailments develop.
"This new study makes a vitally important contribution by helping to map this little-explored territory," said Paul Shattuck, a Drexel University autism researcher who was not involved.
The study was prepared for release Wednesday at the International Meeting for Autism Research in Atlanta. It's based on medical records for 2,100 adults with autism spectrum disorder, an umbrella term encompassing mild autism and the more classic form of the disorder. They were enrolled during 2008-12 in a Kaiser health plan in northern California. Their records were compared with 21,000 non-autistic Kaiser enrollees.
Key results for autistic versus non-autistic adults:
—Depression: 38 per cent vs. 17 per cent.
—Suicide attempts: 1.6 per cent vs. .3 per cent.
—High blood pressure: 27 per cent vs. 19 per cent
—Cholesterol problems: 26 per cent vs. 18 per cent.
—Obesity: 27 per cent vs. 16 per cent.
—Alcohol use: 23 per cent vs. 53 per cent
—Smoking: 16 per cent vs. 30 per cent.
Autism expert David Mandell, director of a mental health policy centre at the University of Pennsylvania, said research is needed to determine if autistic adults are more likely to be diagnosed with other conditions simply because they have more contact with doctors. But Mandell said the disparities are probably real and that the medical community tends to focus mostly on treating behavioural problems in autism. The study highlights a need to focus equally on "these very important health conditions," many of which are preventable, he said.
The government's latest statistics suggest that 1 in 68 U.S. children have autism, or more than 1 million Americans. It's considered a lifelong disorder that can involve language, intellectual and social impairments and unusual, repetitious behaviours.
Some common features, including lack of eye contact and social awkwardness, might suggest that people with autism dislike human contact. But Croen said it's more likely that they share a desire to connect with other people but have trouble doing so. That isolation could lead to problems like depression, she said.
Croen said isolation might also at least partly explain the lower rates of drinking and smoking, since those are social activities.