An examination of early exposure to childhood pets has concluded that there may be an association between such contact and altered rates of development of serious pschiatric disorders later in life.
And results suggest that the earlier in life that exposure to dogs occurs the better.
The study, "Exposure to Household Pet Cats and Dogs in Childhood and Risk of Subsequent Diagnosis of Schizophrenia or Bipolar Disorder", was published last month in PLOS ONE, a peer-reviewd open-access scientific journal.
Lead author Dr. Robert Yolken is a professor of pediatrics at Johns Hopkins University's school of medicine and is a paid scientific advisor to the Stanley Medical Research Institute, a nonprofit that supports research into bipolar disorder and schizophrenia.
The study's 1,371 participants were drawn from various prograns run by the Baltimore-based Sheppard Pratt Health Syatem and affiliated local psychiatric agencies. Of that total, 396 had been diagnosed with schizophrenia, 381 with bipolar, and 594 with no serious psychiatric disorder, as a control group within the cohort.
The purpose of the project was to see if there was a relationship between exposure to a household cat or dog during the first 12 years of life and a diagnosis later in life of either bipolar disorder or schizophrenia.
Apparent benefit for schizophrenia, not bipolar disorder
Accoring to the published results, there were "significant" decreased hazards and relative risks of developing schizophrenia with early exposuer to dogs, but little such evidence with dog contact and the devlopment of bipolar disorder.
"We found that exposure to a household pet dog was associated with a significantly decreased hazard of having a subsequent diagnosis of schizophrenia (Hazard Ratio .75, p < .002)," the PLOS ONE paper stated. "Furthermore, a significant decreased relative risk of schizophrenia was detected following exposure at birth and during the first years of life. There was no significant relationship between household exposure to a pet dog and bipolar disorder."
The paper went on to state that "exposure to a pet dog during the first 12 years of life was associated with an approximately 25% decreased hazard of having a subsequent schizophrenia diagnosis"
But that percentage almost doubled when contact with dogs occured from the earliest stages of life, according to the report: "...the apparent protective effect of exposure to a household pet dog was most evident when the household pet dog was present at birth or was added to the household before the end of the second year of life, with exposure during these time points being associated with an approximately 50% reduction in relative risk of a schizophrenia diagnosis."
Cat exposure seems to have little effect
Regarding any relationship between exposure to cats and subsequent development of psychiatric disorders, the paper stated: "There were no significant associations between exposure to a household pet cat and subsequent risk of either a schizophrenia or bipolar disorder diagnosis. However, there were trends towards an increased risk of both disorders at defined periods of exposure."
Possible explanations for the seeming reduction in risk for schizophrenia after dog exposure put forth for further discussion by the research team involved demographic factors—such as geographic location, parental education, socioeconomic staus, and others—or some kind of immune-system interaction involving "exposure to pet dogs [that] might affect intestinal inflammation and modulate the risk of schizophrenia through changes in the brain-immune-gut axis  or the psycho-immune-neuroendocrine network".
The paper's authors concluded: "An understanding of the mechanisms underlying these associations could provide insights into the role of environmental exposures as risk factors for these disorders and inform appropriate interventions."