Living with Cats May Raise Odds of Schizophrenia-Related Conditions by Almost Twofold

Household cats may nearly double the risk of developing schizophrenia and related conditions, researchers in Australia conclude after analyzing 17 studies carried out across 11 countries over the past 44 years. The work appeared in Schizophrenia Bulletin.

Large Review Finds a Significant Positive Association

The team led by psychiatrist John McGrath from the Queensland Centre for Mental Health Research examined a broad body of scientific evidence and reported a “significant positive association between cat ownership and elevated risk of schizophrenia-spectrum disorders.” The authors caution, however, that the evidence base remains limited and that association does not prove causation.

“Significant positive association between cat ownership and elevated risk of schizophrenia-spectrum disorders,” the review states.

Toxoplasma Hypothesis Remains Under Suspicion

Researchers have suspected the parasite Toxoplasma gondii (T. gondii) since the mid-1990s. Humans can acquire T. gondii via undercooked meat, contaminated water, cat scratches or bites, or contact with infected cat feces. In the United States, about 40 million people carry the parasite, often without symptoms.

Laboratory studies show that T. gondii can enter the central nervous system and influence neurotransmitter systems, and investigators have linked infection to personality changes, psychotic symptoms, and the emergence of certain neurological disorders, including schizophrenia. Still, a detected association does not prove that the parasite causes psychiatric illness or that transmission occurred directly from a household cat.

What Review Actually Shows

The authors found that people who reported contact with cats had roughly twice the odds of developing schizophrenia compared with those without cat contact. Most of the included studies (15 of 17) were case-control designs, which can detect associations but cannot establish cause and effect.

The findings across individual studies varied:

• Some studies linked childhood cat contact to increased schizophrenia risk.
• Other studies found no association.
• One study found no overall risk for children who had cats before age 13 but did observe higher risk among those exposed between ages 9 and 12.
• A study of 354 students reported no difference in schizotypal traits between cat owners and non-owners, yet it found higher measures among students who experienced cat bites.
• Another project associated cat bites with certain psychological symptoms but noted that the bacterium Pasteurella multocida, not T. gondii, might explain those effects.

The review authors emphasize the generally low quality of many earlier studies and highlight the need to account for confounding factors that could influence results.

Researchers Call for Larger, Better Studies

Given the current uncertainties, the authors urge large, well-designed longitudinal studies to determine whether cat ownership represents an independent risk factor for schizophrenia or whether the observed links reflect other environmental, behavioral, or biological variables.