In a recently published study, Steele Children's Research Center investigator and lead author Thomas Ball, MD, associate professor of clinical pediatrics at The University of Arizona and his colleagues found that infants whose mothers have asthma or other allergic disease, had a higher cortisol response to the stress of vaccination at 6 months of age than children of mothers who do not have asthma or other allergic disease. This finding demonstrates the impact of the intrauterine environment on the infant's cortisol stress response.
"This is very interesting and noteworthy because we've historically attributed alterations of the cortisol stress response to be the result of the stress of having chronic disease," explains Dr. Ball. "It now appears that the higher cortisol stress response may precede the onset of disease. Children of mothers with allergic diseases come into the world with a higher cortisol setting-they have their 'thermostat' set higher. Because of this higher cortisol stress response, these children appear at greater risk of developing allergic diseases like asthma."
The researchers also found that postnatal factors that reduce the likelihood of an infant developing asthma and allergic diseases were associated with a lower cortisol stress response. "We found that if infants had older siblings, or attended daycare in the first two months of life, they had a lower cortisol response to the stress of vaccination at 6 months," says Dr. Ball. This is consistent with the hygiene hypothesis, which proposes that early exposure to microbes prevents the subsequent development of allergic disease, since infants exposed to more children at home or in daycare have more infections.
The first three years of life are critical to brain development and because the "control center" for the cortisol stress response is in the brain, it is believed that a child's cortisol response to stress becomes hard-wired during this time period.
"Since cortisol is so interrelated with the immune system, the child's early years are a critical window of opportunity for impacting the development of their immune system," explains Dr. Ball. "This is the time when allergies often begin. If we can modify this response through adequate control of maternal disease during pregnancy and by postnatal exposure to external factors, such as daycare or siblings, we may be able to reduce the likelihood of developing allergic diseases."
