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Owning a cat before age 25 may double the risk of schizophrenia

Could the ownership of a cat increase the risk of schizophrenia? The answer is yes, according to a recent review of 17 studies conducted by researchers from the University of Queensland in Australia.

Focus of the study

In their comprehensive analysis, the team performed a meta-analysis of existing research, published over the last 44 years and spanning 11 countries, including the United States and the United Kingdom. 

What they discovered was that individuals exposed to cats before the age of 25 had approximately double the odds of developing schizophrenia.

Toxoplasma gondii

The scientific rationale behind this correlation lies in a parasite called Toxoplasma gondii, or T. gondii for short, which is commonly found in pet cats. This parasite has the potential to enter the human body through a cat’s bite. 

Once inside, it can infiltrate the central nervous system and influence neurotransmitters in the brain. This, in turn, can lead to alterations in personality, the emergence of psychotic symptoms, and the development of psychiatric disorders, including schizophrenia.

Schizotypy scale

One of the studies included in the review, which focused on 354 students in the United States, did not find a direct link between cat ownership and scores on a schizotypy scale. 

However, when comparing individuals who had been bitten by a cat to those who had not, the bitten group displayed higher scores on the schizotypy scale.

This scale is essentially a questionnaire designed to gauge traits associated with unconventional and disorganized patterns of thinking, often employed in the diagnosis of schizophrenia.

Severe mental disorder 

Schizophrenia is a severe and chronic mental disorder affecting an estimated one percent of the global population, with around two million individuals in the United States alone. 

This condition profoundly impacts how a person thinks, feels, and behaves, often resulting in the affected individual seeming disconnected from reality.

The precise cause of schizophrenia remains elusive, with experts speculating that it may be a combination of genetic factors, abnormalities in brain chemistry, viral infections, and immune disorders. 

Symptoms of schizophrenia 

Symptoms typically manifest between the ages of 16 and 30, although there are rare instances of children being affected as well.

The symptoms of schizophrenia can be categorized into three groups: positive, negative, and cognitive. 

Positive symptoms

Positive symptoms entail disturbances that are “added” to an individual’s personality, encompassing hallucinations, delusions, and thought disorders characterized by unusual or dysfunctional thinking patterns. 

Negative symptoms

Negative symptoms involve the loss of certain capabilities from an individual’s personality, such as “flat affect” (reduced emotional expression through facial expressions or voice tone), decreased pleasure in everyday life, and difficulties initiating and sustaining activities. 

Cognitive symptoms

Cognitive symptoms include alterations in memory and other cognitive functions, including problems with focus, attention, working memory, and the ability to comprehend and use information for decision-making.

Study limitations

Nevertheless, the UQ review has faced criticism on Twitter from other researchers who argue that it did not adequately account for other potential contributing factors, such as social and economic backgrounds and family histories. 

For instance, a British study found an association between childhood cat exposure (between ages four and ten) and increased psychotic-like experiences at age 13, but these findings did not persist after adjusting for potential confounding variables. 

Dr. Sanil Rege, a psychiatrist based in Melbourne, pointed out that 15 out of the 17 included studies were case-control studies known for their susceptibility to spurious associations.

The study is published in the journal Schizophrenia Bulletin.

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