Growing up with a family cat is a significant if improbable commonality among people who develop schizophrenia.
"Cat ownership in childhood has now been reported in three studies to be significantly more common in families in which the child is later diagnosed with schizophrenia or another serious mental illness," wrote the researchers behind a new study published in the journal Schizophrenia Research.
Those researchers -- E. Fuller Torrey and Wendy Simmons of the Stanley Medical Research Institute and Robert H. Yolken of the Stanley Laboratory of Developmental Neurovirology -- looked at an unused 1982 questionnaire that had been distributed to 2,125 families that belonged to the National Institute of Mental Illness, and found that 50.6 percent of people who developed schizophrenia owned a cat in childhood. These results were strikingly similar to two smaller studies conducted among NAMI members in the 1990s that found a 50.9 and 51.9 percent correlation.
Some 1.1 percent of the population has been diagnosed with schizophrenia, while 30-37 percent of American households have a cat, according to the ASPCA.
Of course, this research merely shows a link rather than a causal relationship. But researchers theorize that the parasite Toxoplasma gondii (T. gondii), which is found in cats and can be passed on to humans, could play some role in the development of the mental illness. Schizophrenia affects 2.5 million Americans, according to the Treatment Advocacy Center.
"T. gondii gets into the brain and forms microscopic cysts. We think it then becomes activated in late adolescence and causes disease, probably by affecting the neurotransmitters," Torrey told The Huffington Post.
In addition to schizophrenia, T. gondii is linked to miscarriages, fetal development disorder, flu-related illness, blindness and, in extreme cases, death, according to Time. Although the Centers for Disease Control and Prevention estimate that more than 60 million people in the U.S. have T. gondii, people with strong immune systems generally don't show any symptoms. Researchers suggest keeping cats indoors since T. gondii can be transmitted through neighboring cats, and keeping litter boxes covered, since T. gondii can be transmitted to humans if they accidentally come in contact with cat feces, according to the Mayo Clinic.
Further study is needed to ascertain how big the link between cats and schizophrenia actually is, and the study's authors encouraged researchers in other countries to conduct their own surveys. It's also important to note that the overall instance of schizophrenia is low.
Owning a cat comes with plenty of benefits. According to a 2008 study from researchers at the University of Minnesota's Stroke Institute, cat owners are 30 percent less likely to die of a heart attack. Plus, spending time with pets eases feelings of loneliness, according to the CDC.