The severity of a child’s autism may be directly linked with the level of stress or anxiety they experience on a day-to-day basis, a new study suggests.

Levels of the stress-hormone cortisol remain significantly higher throughout the day in children with low-functioning autism as compared to typically-developing kids and those on the high-functioning end of the spectrum, according to findings published in the Journal of Developmental and Physical Disabilities.

For the study, researchers at Canisius College in Buffalo, N.Y. collected saliva samples three times each day over two different weekends from 43 kids ages 7 to 12. The group included children with no diagnosis as well as kids with autism and an IQ below 70 — considered low-functioning — and high-functioning individuals with IQs above 85.

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All of the children exhibited typical patterns in their cortisol levels, with the hormone at its highest in the morning and getting progressively lower throughout the day. However, the exact amount of cortisol seen in low-functioning children was distinct, researchers found.

“Children with (lower-functioning autism) had significantly higher cortisol, the stress indicator, across the day than both the (high-functioning children with autism) and typical children and, interestingly, children with (high-functioning autism) did not significantly differ from the typical children across the day,” said Susan Putnam of the Institute for Autism Research at Canisius College who led the study.

Putnam and her colleagues said the results point to a link between stress in the body and functioning ability and IQ. However, it is unclear, they said, whether the increased cortisol observed in those with more severe autism is a result of neurological impairment or heightened sensitivity to the environment.