Having a dog, not a cat, as a child may protect against schizophrenia
In news guaranteed to reignite all those simmering dogs versus cats arguments, a study from Johns Hopkins Medicine is suggesting exposure to a household pet dog over a child’s first few years of life can be linked to a lower risk of developing schizophrenia as an adult. The same correlation was not seen in children raised around cats – in fact, a slightly increased risk of developing schizophrenia was detected in children who were in contact with cats between the ages of nine and 12.
“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,” says lead author Robert Yolken, explaining the origins of the research.
The study centered on two conditions: schizophrenia and bipolar disorder. Nearly 1,400 subjects were recruited, a little over half of whom had diagnoses of one of the two conditions, and all were questioned about pet exposure during the first 12 years of life.
The most striking finding was exposure to a pet dog generally meant a person was 24 percent less likely to be diagnosed with schizophrenia as an adult. The strongest result was seen in those subjects raised with a dog from birth.
“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 three,” says Yolken.
There was no association detected linking dogs to either an increased or decreased risk of bipolar disorder. However, while early exposure to cats correlated with a neutral link to later-life diagnosis of either condition, exposure to cats between the ages of nine and 12 showed a slightly increased risk.
“… we did find a slightly increased risk of developing both disorders for those who were first in contact with cats between the ages of nine and 12,” notes Yolken. “This indicates that the time of exposure may be critical to whether or not it alters the risk.”
It is reasonable at this point to be slightly skeptical of these kind of studies that seem to conjure strangely random associations between disparate factors. And, it is fair to cite that classic “correlation is not causation” argument to suggest there may be nothing particularly intrinsic about cat or dog ownership to cause diseases such as schizophrenia to appear later in life. But Yolken and his team suggest there are several logical reasons to explain this strangely protective effect only appearing in dogs.
“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,” says Yolken.
The researchers point out that there are several studies that have found dog ownership and exposure, both during pregnancy and across a child’s first few years of life, to be linked with lower rates of immune-mediated allergy development, including asthma.
On the other hand, the link between cat exposure and schizophrenia is somewhat consistent with studies suggesting cats are more likely to harbor a parasite associated with toxoplasmosis. Prior research has strongly linked this parasite to later life development of schizophrenia, and this new study seems to suggest a child may be most susceptible to this danger between the ages of nine and 12.
Of course, cat owners need not be alarmed. This study in no way is claiming that cat ownership is damaging to a child’s developing mental health. The researchers do stress there are many oblique demographic factors that were not evaluated in the study, including birth order, family size, contact with farm animals, exposure to feral cats and other animals, pre-existing allergic or other disorders, or even breed of dog. Any of these factors could play a role in explaining the study’s conclusion.
And if those cat owners out there still need a bit of reassurance their pet choice is not dangerous they can take comfort in knowing that according to some research, they are ultimately smarter than their dog-owning counterparts.
The new research was published in the journal PLOS One.
Source: Johns Hopkins Medicine