Recent headlines in The New York Times and elsewhere have trumpeted a finding that sounds like great news for animal lovers. Having a pet dog as a child, a new study says, could significantly decrease your risk of developing schizophrenia later in life. But is it too good to be true? Can dogs really prevent severe brain disorders? The answer seems to be “maybe,” but we don’t know why or how.

A Surprising Study

The study, which was conducted by researchers led by Robert H. Yolken, MD, at Johns Hopkins University, was inspired by the knowledge that external environmental influences are a significant factor in the development of brain diseases such as bipolar disorder (BD) and schizophrenia. The study’s authors wanted to see if exposure to pet dogs and cats in childhood had an impact on risk for both diseases. To find out, they compared the pet histories of patients with bipolar disorder or schizophrenia to a control group of healthy participants.

The results showed that exposure to a pet dog seemed to produce a substantial decrease in schizophrenia risk, especially when the exposure began at birth or in infancy. Participants who had a pet dog at any time before the age of 13 saw a 24% decrease in risk, and those who had a dog at birth saw a 55% decrease.

The benefits were confined to schizophrenia. Exposure to a pet didn’t seem to have any effect on bipolar risk.

What About Cats?

Unfortunately for cat lovers, only exposure to dogs seems to have decreased the risk of schizophrenia. Not only did exposure to pet cats not decrease the risk, the risk of both schizophrenia and bipolar disorder actually increased slightly if children were exposed to cats between the ages of 9 and 12.

A Canine Mystery

Given that the cause of schizophrenia is unknown, it’s difficult to say why having a pet dog might prevent the disease. One theory is that problems with the body’s immune system might result in changes in brain chemistry that, in turn, trigger the onset of the disease. Studies have found a connection between schizophrenia and infection in the mother’s body during pregnancy, leading researchers to suspect that the immune system plays a role in the development of the disorder. Some researchers believe, too, that the immune system continues to play a role in the brain’s development throughout infancy.

It’s possible, the current study’s authors believe, that exposure to bacteria associated with dogs could have a beneficial effect on a child’s immune system, leading to a reduction in schizophrenia-associated chemical changes. The authors note that the effect is most pronounced when dogs are present during early childhood when the immune system has a big effect on brain development.

The Truth About Dogs

The study’s authors acknowledge some limitations in their methods. The study data didn’t fully account for differences in socioeconomic status, and it’s possible that dog ownership might be more common in certain socioeconomic communities. If that’s true, social status or household wealth, rather than the dogs themselves, might be the real key to decreased schizophrenia risk.

Another limitation is that the data didn’t include a full accounting of the patients’ physical health, and that could also cloud the picture. For example, both dog ownership and socioeconomic status might be associated with lower body mass index, and that could be the explanation for the lower schizophrenia risk.

The hypothetical connection between dogs and schizophrenia mitigation is a complex one that goes beyond the companionship and devotion that pet dogs offer to their owners. Whatever the cause, though, the connection could be a starting point for new research that furthers our understanding of schizophrenia.

Frontiers in Neuroscience, Role of the Immune System in the Development of the Central Nervous System
Neurology, Maternal immune activation, and abnormal brain development across CNS disorders
Science, Maternal immune activation: Implications for neuropsychiatric disorders
Frontiers in Neuroendocrinology, The Immune System and Developmental Programming of Brain and Behavior

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