Cat Ownership Linked to Higher Odds of Schizophrenia-Related Disorders, Review Finds

A 2023 review of existing evidence suggests that keeping a cat may be associated with greater odds of schizophrenia-related conditions.

This does not mean that your cat is covertly affecting your health.

The researchers at the Queensland Centre for Mental Health Research in Australia stress that the results identify an association rather than a cause-and-effect relationship. More robust research will be required before firm conclusions are possible.

The suggestion that cat ownership could be connected with schizophrenia risk dates to a 1995 hypothesis, which proposed that an infection transmitted from animals to people might be involved.

One possible explanation put forward is exposure to Toxoplasma gondii, a parasite linked with cats.

However, research to date has produced inconsistent findings.

Cat ownership and schizophrenia-related disorders

In their 2023 review and meta-analysis, psychiatrist John McGrath and his colleagues assessed research published during the previous 44 years in 11 countries, including the US and the UK.

They reported "a significant positive association between broadly defined cat ownership and an increased risk of schizophrenia-related disorders."

Schizophrenia is a brain disorder that changes the way someone thinks, feels and behaves. Its precise causes are diverse, complex and largely unknown.

Genetic, environmental and biological alterations in the brain all appear to contribute.

Some studies indicate that contact with cats in childhood could raise the likelihood of developing schizophrenia, although other research has not identified an association.

Certain papers have also associated cat exposure with higher scores on scales assessing schizophrenia-related traits and psychotic-like experiences.

Yet other studies have not found that link.

McGrath and his team set out to gain a clearer understanding of whether there might be a connection between cats and mental health.

"After adjusting for covariates, we found that individuals exposed to cats had approximately twice the odds of developing schizophrenia," they write in their published paper.

Of the 17 studies considered in the review, one found no significant relationship between owning a cat before the age of 13 and developing schizophrenia later in life.

However, that same study did find a significant association when it focused on a particular ownership period, from ages 9 to 12.

This variation indicates that the key period during which cat exposure may matter has not been clearly established.

Toxoplasma gondii and potential infection pathways

T. gondii is a parasite that can pass to people through the faeces of an infected cat.

Transmission can also occur through undercooked meat or contaminated water.

The CDC estimates that more than 40 million people in the US carry T. gondii, usually without experiencing symptoms.

Scientists are continuing to uncover unusual effects that infections may produce.

After entering the body, T. gondii can remain in the central nervous system and may affect neurotransmitter systems.

The parasite has been associated with changes in personality, the development of psychotic symptoms and certain brain disorders, including schizophrenia.

Nevertheless, an association does not demonstrate that T. gondii causes these changes, nor does it establish that a cat transmitted the parasite to a person.

A further study included in the review involved 354 psychology students in the US and found no relationship between cat ownership and schizotypy scores.

People who had been bitten by a cat, however, recorded higher scores than those who had not been bitten.

Other research involving people both with and without mental disorders found an association between cat bites and elevated scores on tests that assess particular psychological experiences.

The authors of that research proposed that other pathogens, including Pasteurella multocida, could be responsible.

Limitations of the existing evidence

Several important limitations need to be considered, not least that 15 of the 17 reviewed papers were case-control studies.

This research design cannot establish cause and effect, and it frequently fails to account for factors that may influence both the exposure and the outcome.

The researchers also note that several of the studies they assessed were of low quality.

Findings differed between studies, while the higher-quality evidence indicated that associations seen in unadjusted models could be accounted for by other factors that may have affected the results.

According to the authors, the field requires better-designed studies that can account more thoroughly for confounding factors.

"Our review provides support for an association between cat ownership and schizophrenia-related disorders," McGrath and colleagues conclude.

"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."

The research appeared in Schizophrenia Bulletin.

An earlier version of this article was published in December 2023.