Early-life exposure to dogs may lessen risk of developing schizophrenia

Ever since humans domesticated the dog, the faithful, obedient and protective animal has provided its owner with companionship and emotional well-being. Now, a study from Johns Hopkins Medicine suggests that being around “man’s best friend” from an early age may have a health benefit also — lessening the prospect of developing schizophrenia as an adult.

And while Fido may help prevent that condition, the jury remains out on whether or not there’s any link, positive or negative, between being raised with Fluffy the cat and later developing either schizophrenia or manic depression .

“Serious psychiatric disorders are related to alterations within the system linked to environmental exposures in youth , and since household pets are often among the primary things with which children have close contact, it had been logical for us to explore the chances of a connection between the 2 ,” says Robert Yolken, M.D., chair of the Stanley Division of Pediatric Neurovirology and professor of neurovirology in pediatrics at the Johns Hopkins Children’s Center, and lead author of a search paper recently posted online within the journal PLOS One.

In the study, Yolken and colleagues at Sheppard Pratt Health System in Baltimore investigated the connection between exposure to a household pet cat or dog during the primary 12 years of life and a later diagnosis of schizophrenia or manic depression . For schizophrenia, the researchers were surprised to ascertain a statistically significant decrease within the risk of an individual developing the disorder if exposed to a dog early in life. Across the whole age range studied, there was no significant link between dogs and manic depression , or between cats and either psychiatric disorder.

The researchers caution that more studies are needed to verify these findings, to look for the factors behind any strongly supported links, and to more precisely define the particular risks of developing psychiatric disorders from exposing infants and youngsters under age 13 to pet cats and dogs.

According to the American Pet Products Association’s most up-to-date National Pet Owners Survey, there are 94 million pet cats and 90 million pet dogs within the us . Previous studies have identified youth exposures to pet cats and dogs as environmental factors which will alter the system through various means, including allergic responses, contact with zoonotic (animal) bacteria and viruses, changes during a home’s microbiome, and pet-induced stress reduction effects on human brain chemistry.

Some investigators, Yolken notes, suspect that this “immune modulation” may alter the danger of developing psychiatric disorders to which an individual is genetically or otherwise predisposed.

In their current study, Yolken and colleagues checked out a population of 1,371 men and ladies between the ages of 18 and 65 that consisted of 396 people with schizophrenia, 381 with manic depression and 594 controls. Information documented about everyone included age, gender, race/ethnicity, place of birth and highest level of parental education (as a measure of socioeconomic status). Patients with schizophrenia and manic depression were recruited from inpatient, day hospital and rehabilitation programs of Sheppard Pratt Health System. Control group members were recruited from the Baltimore area and were screened to rule out any current or past psychiatric disorders.

All study participants were asked if that they had a household pet cat or dog or both during their first 12 years of life. those that reported that a pet cat or dog was in their house once they were born were considered to be exposed thereto animal since birth.

The relationship between the age of first household pet exposure and psychiatric diagnosis was defined employing a statistical model that produces a hazard ratio — a measure over time of how often specific events (in this case, exposure to a household pet and development of a psychiatric disorder) happen during a study group compared to their frequency during a control group. A hazard ratio of 1 suggests no difference between groups, while a ratio greater than 1 indicates an increased likelihood of developing schizophrenia or manic depression . Likewise, a ratio but 1 shows a decreased chance.

Analyses were conducted for four age ranges: birth to three , 4 to 5, 6 to eight and 9 to 12.

Surprisingly, Yolken says, the findings suggests that folks who are exposed to a pet dog before their 13th birthday are significantly less likely — the maximum amount as 24% — to be diagnosed later with schizophrenia.

“The largest apparent protective effect was found for youngsters who had a household pet dog at birth or were first exposed after birth but before age 3,” he says.

Yolken adds that if it’s assumed that the hazard ratio is an accurate reflection of relative risk, then some 840,000 cases of schizophrenia (24% of the three .5 million people diagnosed with the disorder within the United States) could be prevented by pet dog exposure or other factors related to pet dog exposure.

“There are several plausible explanations for this possible ‘protective’ effect from contact with dogs — perhaps something within the canine microbiome that gets passed to humans and bolsters the system against or subdues a genetic predisposition to schizophrenia,” Yolken says.

For manic depression , the study results suggest there’s no risk association, either positive or negative, with being around dogs as an infant or young child.

Overall for all ages examined, early exposure to pet cats was neutral because the study couldn’t link felines with either an increased or decreased risk of developing schizophrenia or manic depression .

“However, we did find a rather increased risk of developing both disorders for those that were first in touch with cats between the ages of 9 and 12,” Yolken says. “This indicates that the time of exposure could also be critical as to if or not it alters the danger .”

One example of a suspected pet-borne trigger for schizophrenia is that the disease toxoplasmosis, a condition during which cats are the first hosts of a parasite transmitted to humans via the animals’ feces. Pregnant women are advised for years to not change cat litter boxes to eliminate the danger of the illness passing through the placenta to their fetuses and causing a miscarriage, stillbirth, or potentially, psychiatric disorders during a child born with the infection.

In a 2003 review paper, Yolken and colleague E. Fuller Torrey, M.D., associate director of research at the Stanley Medical Research Institute in Bethesda, Maryland, provided evidence from multiple epidemiological studies conducted since 1953 that showed there is also a statistical connection between an individual exposed to the parasite that causes toxoplasmosis and an increased risk of developing schizophrenia. The researchers found that an outsized number of individuals in those studies who were diagnosed with serious psychiatric disorders, including schizophrenia, also had high levels of antibodies to the toxoplasmosis parasite.

Because of this finding et al. love it , most research has focused on investigating a possible link between early exposure to cats and psychiatric disorder development. Yolken says the foremost recent study is among the primary to think about contact with dogs also .

“A better understanding of the mechanisms underlying the associations between pet exposure and psychiatric disorders would allow us to develop appropriate prevention and treatment strategies,” Yolken says.

Working with Yolken on the research team are the subsequent members from Sheppard Pratt Health System: Cassie Stallings, Andrea Origoni, Emily Katsafanas, Kevin Sweeney, Amalia Squire, and Faith Dickerson, Ph.D., M.P.H.

The study was largely supported by grants from the Stanley Medical Research Institute.

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