Do Household Pet Exposures in Children Reduce the Risk of Later Psychiatric Disorders?

Written by Joyce Smith, BS. Early life exposure to household pet dogs may lessen the risk of developing schizophrenia.

Schizophrenia and bipolar disorder carry worldwide morbidity and mortality, with genetic influences differing greatly among different populations ¹. The immune system, influenced by both our environment and genes, is a modulator of brain development ², and may play an important role in the etiology and pathogenesis of schizophrenia and bipolar disorder ³. Previous studies have shown that early life exposure to household pets such as cats and dogs have influenced the immune systems in infants and children through various mechanisms such as regulating the allergic response to allergens ⁴, exposure to zoonotic (animal) bacteria and viruses ⁵, changes in a home’s microbiome ⁶, and pet-induced stress-  reduction effects on human brain chemistry ⁷. Conversely, pet dog exposure during pregnancy, infancy, or childhood has been associated with decreased inflammation and a reduction in immune-mediated disorders such as asthma and food allergies ⁸, findings which are consistent with what has been characterized as the “hygiene hypothesis” ⁹ (that early-life exposure to pets or siblings protects against allergic diseases).

Yolkem and colleagues ¹⁰ investigated whether an association existed between exposure to a household pet dog or cat during the first 12 years of life and a later diagnosis of schizophrenia or bipolar disorder and whether immune modulation might alter the risk of developing psychiatric disorders to which a person has a genetic predisposition. Data was obtained on 1,371 and women, aged 18 to 65, of which 396 had schizophrenia, 381 had bipolar disorder, and 594 had no current or past psychiatric disorders. Included was data on gender, race/ethnicity, birthplace, and highest level of parental education (as a measure of economic status). All participants lived with a household pet dog or cat during their first 12 years of life and were considered exposed since birth if a pet was in their home at time of birth. Analysis was done for age groups: age 3, 4 to 5, 6 to 8, and 9 to12.

• Overall 220 (55.7%) of participants with schizophrenia were exposed to a household pet dog before their 13th birthday compared to 248 (65.2%) with bipolar disorder, and 389 (62.1%) of controls. Regarding household pet cats, 139 (35.1%) of participants with schizophrenia were exposed to a pet cat before the 13th birthday compared to 157 (41.2%) with bipolar disorder and 206 (34.7%) of the control individuals.
• Children exposed to a pet dog before their 13^th birthday were significantly less likely (up to 24%) to be diagnosed with schizophrenia (Hazard Ratio .75, P<0.002), while children who had a household pet dog at birth or who were first exposed after birth but before age 3 were most protected.
• Across all ages studied, there was no significant relationship between pet dogs and bipolar disorder, or between cats and either bipolar disorder or schizophrenia.

Additional studies are recommended to confirm these findings.

Source: Yolken, Robert, Cassie Stallings, Andrea Origoni, Emily Katsafanas, Kevin Sweeney, Amalia Squire, and Faith Dickerson. “Exposure to household pet cats and dogs in childhood and risk of subsequent diagnosis of schizophrenia or bipolar disorder.” PloS one 14, no. 12 (2019).

© 2019 Yolken et al. This is an open access article distributed under the terms of the Creative Commons Attribution License.

Click here to read the full text study.

Posted February 3, 2020.

Joyce Smith, BS, is a degreed laboratory technologist. She received her bachelor of arts with a major in Chemistry and a minor in Biology from  the University of Saskatchewan and her internship through the University of Saskatchewan College of Medicine and the Royal University Hospital in Saskatoon, Saskatchewan. She currently resides in Bloomingdale, IL.

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