|A new study by John Hopkins School of Medicine researchers revealed that having a pet dog while young reduces the risk of schizophrenia or bipolar disorder later in life but the same cannot be said for owning a cat / Photo by: PaylessImages via 123RF|
A new study by John Hopkins School of Medicine researchers revealed that having a pet dog while young reduces the risk of schizophrenia or bipolar disorder later in life but the same cannot be said for owning a cat.
The study, which appeared in the journal PLOS One, details that exposure to household dogs in the first 12 years of life reduces one's risk of developing schizophrenia.
Schizophrenia is a severe and chronic mental disorder that affects how a person behaves, feels, and thinks. It usually appears in early adulthood or late adolescence and is characterized by hallucinations, delusions, and other cognitive difficulties. Many people with schizophrenia resist treatment because they believe that nothing is wrong with them and clear symptoms are only observed once the person begins explaining what they are thinking.
Our World in Data, a platform that provides data and research on global problems, estimated that there were about 20 million people in the world with schizophrenia in 2017 and its prevalence was slightly higher in men (0.26%) than women (0.25%). Countries with a high share of population with schizophrenia include Australia (0.36%), New Zealand (0.34%), China (0.34%), Canada (0.32%), United States (0.33%), and Ireland (0.335). These figures are based on epidemiological and medical data, meta-regression modeling, and surveys.
Meanwhile, countries with a high prevalence of bipolar disorder in 2017 were New Zealand (1.215), Australia (1.14%), Brazil (1.11%), Sweden (1.065), Finland (1.01%), and United Kingdom (1.09%).
|Schizophrenia is a severe and chronic mental disorder that affects how a person behaves, feels, and thinks. It usually appears in early adulthood or late adolescence and is characterized by hallucinations, delusions, and other cognitive difficulties / Photo by: Katarzyna Białasiewicz via 123RF|
Early Life Pet Exposure and Immune Modulation
In the study of the John Hopkins research team, they looked at about 1,371 men and women who were between 18 and 65 years old. Out of the 1,371 subjects, 396 of them were diagnosed with schizophrenia and 381 with bipolar disorder. The remaining 594 were controls. The data documented about the subjects included their ethnicity or race, gender, age, and the highest level of parental education to measure their socioeconomic status. All of these participants were then asked if they owned a dog or cat in the first 12 years of their life.
It was found that those who were exposed to dogs before reaching 13 years old were less likely (24%) to be diagnosed with a mental disorder.
Robert Yolken from the Stanley Division of Developmental Neurovirology and colleagues explained that serious psychiatric disorders have been previously linked with changes in the immune system that are also associated with early-life environmental exposures. Household pets are among the first things that kids have close contact with. Thus, it is logical to study the possible connection between the two. Further, Yolken and colleagues suspected that it may be due to immune modulation.
Exposure to Zoonotic Microbial Agents
By immune modulation, the team means that exposure to zoonotic microbial agents while young alters the body’s microbiome and also creates neuroendocrine effects of stress reduction when owning a pet.
The research team defined the relationship between pet ownership and psychiatric diagnoses utilizing the statistical model that produces what is called the hazard ratio. In prospective studies, the hazard ratio is used to know how often certain events happen compared to the frequency of those in the control group. The hazards described in their study focused on exposure to household pets as well as the development of mental disorders. A hazard ratio that is higher than 1 means an increased likelihood of developing bipolar disorder or schizophrenia.
Yolken said that surprisingly, children who had a household pet dog while they were young had the largest protective effect based on the decreased hazard ratio. They theorized that there is something in the canine microbiome that is passed onto humans and helps boost their immune system or subdues the schizophrenia genetic predisposition.
There was no associated risk when it came to bipolar disorder. Early-life exposure to cats likewise showed a neutral effect. Thus, no link was found between felines and the decreased or increased risk of developing bipolar disorder or schizophrenia. However, they found a “slightly increased risk” of developing a mental disorder for individuals who were in contact with felines between 9 and 12 years old. This means that the period of exposure could be a significant factor when measuring the risk of one's developing the disorder.
|The group thinks that the disease toxoplasmosis could be one of the reasons for a pet-borne trigger of the mental disorder. It is a parasitic disease, wherein felines are the main hosts of the parasites transmitted to humans through animal feces / Photo by: Kateryna Kon via 123RF|
The group thinks that the disease toxoplasmosis could be one of the reasons for a pet-borne trigger of the mental disorder. It is a parasitic disease, wherein felines are the main hosts of the parasites transmitted to humans through animal feces. This is the reason why pregnant women are not advised to change cats' litter boxes and avoid contact with cat feces to prevent the risk of toxoplasmosis, which may cause stillbirth, miscarriage, or even a psychiatric disorder in the baby.
The bond between people and pets is known to decrease blood pressure, bring happiness, and lower stress, among other health benefits. Yolken and the team’s research provides us with a better understanding of the link between psychiatric disorders and pet exposure, which can consequently help people develop further treatment and prevention strategies.