Psychiatric disorders and pets: Can exposure to pets when young influence schizophrenia and bipolar diagnosis?
Pets are good for us. They help us have better health and simply make us feel good. Exposure to pets when young may even decrease allergies in later life. But could they also affect the development of serious psychiatric disorders like schizophrenia and bipolar disorder? Are psychiatric disorders and pets linked?
Psychiatric disorders and pets
Environmental exposures in early life have been associated with psychiatric disorders such as schizophrenia and bipolar disorder. These environmental factors may also interact with genetic factors to result in the disease. It is always going to be complicated to sort out nature versus nurture and their interaction. For people, like us, who are interested in pets, it would be very interesting to figure out if pets had a role in increasing or decreasing subsequent disease diagnosis.
Contact with household pets such as cats and dogs is, of course, one form of environmental exposure. Recent research has investigated the relationship between exposure to a pet cat or dog during the first 12 years of life and having a subsequent diagnosis of schizophrenia or bipolar disorder. People investigated included 396 individuals with schizophrenia, 381 with bipolar disorder, and 594 controls.
Does exposure to a pet affect schizophrenia or bipolar diagnosis?
Exposure to a household dog was associated with a significantly decreased subsequent diagnosis of schizophrenia. Exposure at birth and during the first years of life resulted in a decreased schizophrenia risk but later ages did not show such a decreased risk.
Overall, exposure to a pet dog during the first 12 years of life was associated with an approximately 25% decreased subsequent schizophrenia diagnosis. When the dog was present at birth or was added to the household before the end of the second year of life, there was an approximately 50% reduction.
Dog exposure did not affect the diagnosis of bipolar disorder.
Pet cats did not influence subsequent schizophrenia or bipolar disorder diagnosis. However, there were trends towards an increased risk of both disorders at defined periods of exposure. For instance, there was a trend towards an increased risk of a schizophrenia diagnosis in individuals first exposed to a pet cat between the ages of 9 and 12. And also a trend towards an increased relative risk of bipolar disorder in individuals exposed to a cat after birth through the second year of life.
How can pets affect psychiatric disorders?
Pets, or perhaps more specifically dogs, may affect psychiatric disorders by one of a combination of factors including our immune systems and our microbiome.
The immune system may play an important role in the cause and subsequent development of diseases such as schizophrenia and bipolar disorder and, in early life, the immune system may play a role as a modulator of brain development.
Early life exposures to household pet animals such as cats and dogs have been identified as common environmental factors which can influence our immune system.
Exposure to Dogs
Exposure to a dog during pregnancy, infancy, or childhood has been associated with a decreased rate of immune-mediated disorders such as asthma and food allergies.
Exposure to a household pet dog can alter the intestinal microbiome of human family members through contact with canine microflora.
So, exposure to pet dogs might affect intestinal inflammation and alter the schizophrenia risk through changes in the brain-immune-gut axis or the psycho-immune-neuroendocrine network.
Exposure to a dog while pregnant or during the first 3 years of life corresponds to the time periods where immune activation has been associated with altered neurodevelopment and an increased risk of psychiatric disorders.
Exposure to a household pet dog has also been associated with a lower rate of depression and anxiety in children aged 4–7.
Exposure to Cats
The relationship between household exposure to a pet cat during infancy and childhood and subsequent schizophrenia has been previously studied and an association found with an increased rate of adult schizotypal traits and also an increased rate of schizotypal traits in adults with a history of childhood cat bites. In adolescents, however, cat exposure was not significantly associated with psychotic experiences.
These differences may be due to differences in social, demographic and biological variables, which were accounted for in this current study. It does seem as if the age of first pet cat exposure may be important in terms of disease risk, as it is with dogs.
It seems a little unclear why dogs may decrease psychiatric disorder diagnosis but cat’s slightly increase the risk. Perhaps owners are more likely to choose one or the other based on their genetic predispositions. So much we have still to find out!