SYDNEY, Nov 17: Owning a cat could potentially double a person’s risk of developing schizophrenia-related conditions, according to an analysis of 17 studies conducted by researchers at the Queensland Centre for Mental Health Research in Australia.

Psychiatrist John McGrath and colleagues reviewed research published over the past 44 years in 11 countries, including the United States and the United Kingdom. Their 2023 review found “a significant positive association between broadly defined cat ownership and an increased risk of schizophrenia-related disorders.”

“There is a need for more high-quality studies in this field,” the authors emphasized in their published paper.

The idea that cat ownership might be linked to schizophrenia risk was first suggested in a 1995 study, with exposure to the parasite Toxoplasma gondii proposed as a potential cause. Research so far has produced mixed findings, with some studies indicating that exposure to cats during childhood may increase the likelihood of developing schizophrenia, while others show no significant association.

Some studies also suggest that cat exposure is linked to higher scores on scales measuring schizophrenia-related traits and psychotic-like experiences, though these results are inconsistent. McGrath and his team stress the need for a comprehensive review of all research in this area to better understand potential links.

T. gondii is a mostly harmless parasite that can be transmitted through undercooked meat, contaminated water, or contact with infected cat feces. Estimates suggest around 40 million people in the United States carry the parasite, typically without symptoms. Research has linked T. gondii infection to changes in the central nervous system and neurotransmitters, potentially contributing to personality changes, psychotic symptoms, and neurological disorders, including schizophrenia.

“After adjusting for covariates, we found that individuals exposed to cats had approximately twice the odds of developing schizophrenia,” the Australian team wrote.

However, the researchers cautioned that 15 of the 17 studies were case-control studies, which cannot prove cause and effect and often do not account for factors that may influence both exposure and outcome. They also noted the low quality of several studies.

One study found no significant association between owning a cat before age 13 and later schizophrenia, but did identify a link when focusing on ownership between ages 9 and 12, suggesting a critical exposure window that remains unclear. A U.S. study involving 354 psychology students found no connection between cat ownership and schizotypy scores, although participants who had been bitten by a cat scored higher. Another study linked cat bites to elevated scores on psychological assessments but suggested other pathogens, such as Pasteurella multocida, could also play a role.

“Our review provides support for an association between cat ownership and schizophrenia-related disorders,” the authors concluded. “There is a need for more high-quality studies, based on large, representative samples, to better understand cat ownership as a candidate risk-modifying factor for mental disorders.”