No, having a cat does not increase your risk of developing schizophrenia.

It’s Science Fiction with Stuart Ritchie, a newsletter exclusively for i-subscribers. If you’d like to receive it straight to your inbox every week, sign up here.

Here’s a question you’ve probably never thought about: Does owning a cat increase your risk of developing schizophrenia? To be honest, I didn’t even think about it until a new study came out this week that tried to answer this very question.

What is the mechanism? So why might having a cat cause you to experience symptoms of psychosis? Some scientists argue that the answer lies in toxoplasmosis. Cats are considered masters Toxoplasma gondii, a microscopic parasite. Experiments have shown that rats, when infected T. gondiiBehave in more risky ways to increase the likelihood that the cat will eat them, allowing the parasite to spread and multiply.

People suffering from acute toxoplasmosis, a disease associated with it T. gondii Infection – may have only mild or no physical symptoms. But people with weaker immune systems may develop something worse: in some cases, neurological symptoms such as hallucinations and delusions may occur.

And this is the first clue that interests scientists: symptoms of schizophrenia and toxoplasmosis may include both hallucinations and delusions. Maybe a link? Some previous reviews of the scientific literature have definitely shown that people with schizophrenia have a higher risk of developing schizophrenia. T. gondii than the average person.

Then we need a few more links in the chain. Does having a cat as a pet increase your risk of developing diabetes? T. gondii Infection? This is true. And then: does having a cat increase the risk of schizophrenia?

That’s exactly what the new study wanted to find out.

Paws for thinking (disorder)

Before we begin, consider the following, which could make this idea more or less scary depending on the situation: We are talking about contact with cats. in young age. Schizophrenia is usually diagnosed in your twenties; In the new observational study, researchers only looked at cases where exposure to cats occurred before the age of 25.

When they looked at all the studies on cats and schizophrenia, they found seventeen that fit this pattern: they had to have some degree of schizophrenia and some degree of early exposure to cats in life. Of course, these weren’t experiments: it’s not like they gave some people a cat and tested their mental health years later compared to a control group that didn’t have cats. These were mostly case-control studies in which people with the disease were compared with similar people without the disease.

Overall, the results were quite clear: owning a cat was associated with a higher risk of schizophrenia. People exposed to cats early in life were slightly more than twice as likely to develop the disease, which is a fairly significant association.

The first analysis found that the reason for this result may have been an unusual study that found cat owners were 16 times more likely to be at risk: if it had come down to just one study, this would have been the overall result. not to be the same. was just as reliable. But in another analysis that took into account many factors such as age, sex, education, etc. – and no longer had such a dramatic outlier – the result was essentially the same: cats had a twice the risk of schizophrenia.

So that’s it? Will this answer our question and make us believe that cats cause schizophrenia?

Not so fast.

Claws and effect

In addition to summarizing the studies to see the overall result, the researchers also examined Quality every study. You can rate this on a scale from 0 to 9. For example, how representative was the survey of the entire population? How reliable were the measures of both incidence and exposure (for example, relying on people’s memories of having a cat thirty years ago may be less informative). Were there gaps in who responded? (If everyone in the control group answered the questionnaire, but not everyone in the disease group, this could skew your results.) And so on.

The authors found that eight studies had a score of four or less; nine had a score above five. However, many of the studies were of fairly poor quality, meaning that various biases and errors can cause the results to differ from reality – in other words, we may be fooling ourselves into including them in our overall picture.

Some higher quality studies, such as a 2017 study from the UK, found no link between cat ownership and psychosis; Another high-quality study conducted in Finland in 2019 found only the smallest and most borderline association between cats and symptoms of psychosis.

If you look at some of the other studies that were considered high quality, such as the 2022 study in Canada, you don’t get the impression that there was a strong effect: the link between cats and schizophrenia depended on whether the person had the disease. a person and a cat a rodent catcher (very specific associations in such studies, if not predicted in advance, are often a signal that this is a statistical coincidence and not a real connection).

A closer look at the research undermined my confidence that the link between cats and schizophrenia is real. And in fact, the authors of the new study are hardly saying that we now have convincing evidence that exposure to cats definitely causes schizophrenia. Instead, they write that “higher-quality studies based on large, representative samples are needed to better understand that cat ownership is a possible risk-modifying factor for mental disorders.”

It’s hard to disagree. There may be something interesting going on, but without a series of better studies to actually pinpoint what’s going on, no one should be too worried about their beloved pet driving them—literally—crazy.

Science Link of the Week

As discussed in this article, we shouldn’t get too excited just yet, but we now have real-life human data showing that semaglutide – the chemical in the weight-loss drugs you’ve heard so much about this year – can help with alcoholism – and also substance use disorders.

It’s Science Fiction with Stuart Ritchie, a newsletter exclusively for i-subscribers. If you’d like to receive it straight to your inbox every week, sign up here.