The researchers found that among the caregivers, even though they had normal cortisol levels in their blood, the pattern of gene expression in a type of white blood cell involved in the body's immune response, was altered so that they were relatively less responsive to the anti-inflammatory actions of cortisol.
Corresponding author Gregory Miller of the University of British Columbia said that although "caregivers have similar cortisol levels as controls, their cells seem to be 'hearing' less of this signal.
"In other words, something goes awry in caregivers' white blood cells so they are not able to 'receive' the signal from cortisol that tells them to shut down inflammation," Miller said in a statement.
The study, published in the journal Biological Psychiatry, said the findings might help to explain why the caregivers would seem to be in a chronic pro-inflammatory state, a condition of immunologic activation. This activated state could contribute to the risk for a number of medical illnesses, such as depression, heart disease and diabetes, the study said.