Persons having cats as pet could double the risk of developing schizophrenia-related disorders, says a new study.
Australian researchers analyzed 17 studies conducted over the past 44 years across 11 countries, including the US and the UK. Psychiatrist John McGrath worked with his team from the Queensland Centre for Mental Health Research. They detailed their findings in a study published last December.
“We found an association between broadly defined cat ownership and increased odds of developing schizophrenia-related disorders,” McGrath explained.
HISTORICAL CONTEXT
The hypothesis linking cat ownership to schizophrenia dates back to a 1995 study. It proposed that exposure to the parasite Toxoplasma gondii might play a role. Nonetheless, research has produced mixed results over the years.
Some studies suggest that childhood exposure to cats could elevate the risk of developing schizophrenia. Conversely, not all research confirms this connection.
MIXED FINDINGS ON SCHIZOPHRENIA TRAITS
Several studies suggest a correlation between cat exposure and higher scores on scales measuring schizophrenia-related traits and psychotic experiences. Yet, inconsistencies remain, as other studies fail to show this association.
To clarify these findings, McGrath and his team advocate for comprehensive reviews of existing research on this topic.
UNDERSTANDING TOXOPLASMA GONDII
Toxoplasma gondii is a mostly harmless parasite that can be transmitted through undercooked meat or contaminated water. It can also spread through bites or feces of infected cats. Approximately 40 million people in the US are estimated to be infected, often without any symptoms.
Once in the body, T. gondii can infiltrate the central nervous system, potentially influencing neurotransmitters. The parasite has been linked to personality changes and the emergence of psychotic symptoms, including schizophrenia.
Nonetheless, it’s essential to note that a correlation does not imply causation. The research does not definitively prove that T. gondii causes these changes or that the parasite is transmitted from cats to humans.
LIMITATIONS OF THE RESEARCH
It is crucial to consider some limitations of these findings. Fifteen of the 17 studies analyzed were case-control studies, which cannot establish cause and effect. These studies often fail to handle factors that might influence both the exposure and the outcome.
Moreover, many of the studies assessed were of low quality. The authors acknowledge that findings were inconsistent, with higher-quality studies suggesting that earlier associations might be influenced by confounding variables.
One study found no significant link between owning a cat before age 13 and later developing schizophrenia. Yet, it did find a connection when focusing on cat ownership during specific ages (9 to 12). This inconsistency highlights the need for clarity about critical time frames for cat exposure.
ADDITIONAL RESEARCH INSIGHTS
In a separate study involving 354 psychology students, researchers found no connection between cat ownership and schizotypy scores. Yet, those who had experienced a cat bite exhibited higher scores than those who had not.
Another study involved individuals with and without mental disorders. Researchers discovered a link between cat bites and elevated scores on tests. These tests measure specific psychological experiences. Researchers suggested that other pathogens like Pasteurella multocida, might contribute to these associations.
The study was published in Schizophrenia Bulletin.