The next time you mull over the idea of getting a pet dog while you have a toddler at home, you probably should act in favour of it. A new study by researchers from Johns Hopkins suggests that exposure to household dogs among children below the age of twelve can reduce the risk of them being diagnosed with schizophrenia in adulthood.
"Serious psychiatric disorders have been associated with alterations in the immune system linked to environmental exposures in early life, and since household pets are often among the first things with which children have close contact, it was logical for us to explore the possibilities of a connection between the two," said Robert Yolken, MD, lead author of the study, in a statement.
The researchers tried to ascertain if the exposure to a pet—a cat or a dog—within the first 12 years of an individual's life—had any links with the chances of them developing bipolar disorder or schizophrenia as adults. While they found no connection between exposure to dogs in childhood and bipolar disorder, they found that when exposed to dogs before they turned 13, there was a significant decrease in the number of people developing and being diagnosed with schizophrenia later in life.
The population studied to understand the link
For the study, 1,371 men and women between the ages of 18 and 65 were chosen. Of these, 396 people were schizophrenic, 381 had bipolar disorder and the remaining 594 were people without any past records of psychiatric disorders. Information such as an individual's age, place of birth, gender, race/ethnicity, and the highest level of parental education were collected.
They were also asked the most important question: Did they have a household pet cat or dog, or both, during the first twelve years of their life? Those who were born into houses that already had pets were considered to be exposed since birth.
In order to study this link and define it, the team used a statistical tool that produces a hazard ratio—which is a measure over time of how often specific events happen in a study group against their frequency in a controlled group. Birth to 3 years, 4 to 5 years, 6 to 8 years and 9 to 12 years, where the age ranges chosen for the study.
Exposure may protect 24 percent of the people from schizophrenia
The findings of the study presented a very interesting connection. Those who were exposed to a pet dog before the age of 13 had fewer chances of receiving a diagnosis of schizophrenia in the future. According to Yolken, if hazard ratio can be considered to accurately reflecting relative risk, then nearly 840,000 cases of schizophrenia, which is 24 percent of the 3.5 million people annually diagnosed with the disorder in the US, may not develop the condition at all.
"The largest apparent protective effect was found for children who had a household pet dog at birth or were first exposed after birth but before age 3," Yolken added, in the statement.
However, no link—positive or negative—was found between bipolar disorder and exposure to dogs at a young age. Additionally, no general positive or negative link could be established between exposure to cats and children across the analysed age range, for either of the disorders.
What is the explanation for the link?
"There are several plausible explanations for this possible 'protective' effect from contact with dogs -- perhaps something in the canine microbiome that gets passed to humans and bolsters the immune system against or subdues a genetic predisposition to schizophrenia," Yolken said.
However, Yolken pointed out that the exposure to felines among children within the age range of 9 and 12, showed a slightly increased risk of developing both of the disorders. "This indicates that the time of exposure may be critical to whether or not it alters the risk," Yolken deliberated.
A possible trigger for schizophrenia due to cat exposure could be toxoplasmosis—a disease where cats are primary hosts of a parasite that is transmitted to humans through its faecal matter.