Living with a cat during childhood does not cause mental illness later in life, a new study from University College London suggests, disputing earlier studies that caused alarm by linking cats to human mental illness.
"We found that children who were born and raised in households that included cats at any time period – that is, pregnancy, early and late childhood – were not at a higher risk of having psychotic symptoms when they were 13 or 18 years old," researchers wrote in The Conversation. The study was published in the journal Psychological Medicine on Wednesday.
The researchers used data from 5,000 children who took part in the Avon Longitudinal Study of Parents and Children, which tracks the health of people born in 1991 and 1992:
We studied whether mothers who owned a cat while pregnant; when the child was four years old; and 10 years old, were more likely to have children who reported psychotic symptoms, such as paranoia or hallucinations, at age 13 and 18 years of age. Although most people who experience psychotic symptoms in adolescence will not develop psychotic disorders later in life, these symptoms often indicate an increased risk for such disorders and other mental illnesses, including depression.
So are cats bad for your mental health? Probably, not.
The findings are especially relevant since previous research suggested that there is a correlation between cat ownership in childhood and developing schizophrenia.
Researchers have previously theorized the culprit could be the parasite Toxoplasma gondii, which separate studies have linked to mental health problems. Toxoplasma gondii can be transmitted through the feces of infected cats, though people can also contract the parasite from eating undercooked meat or unwashed vegetables.
But UCL researchers say prior research linking cat ownership to mental illness was seriously flawed.
"They relied on small samples, did not specify how participants were selected, and did not appropriately account for the presence of missing data and alternative explanations," they wrote. "This can often lead to results that are born out of chance or are biased."
For this study, researchers followed the same children over time, and controlled for variables like income, ethnicity, and other risk factors.
It's also possible that hygiene practices surrounding cats' litter boxes have generally improved over time ― meaning there would be less of a risk that children born more recently would ever get exposed to the parasite in the first place, lead researcher Francesca Solmi told HuffPost.
Other scientists have also expressed skepticism about the trope of cats causing mental illness.
"The scientific problem with every one of these studies is that the populations studied are too small to gain meaningful insights," Dartmouth College microbiology and immunology professor David J. Bzik told Brain Decoder. "With the human stories, there currently is no hard or definitive evidence that Toxoplasma causes behavioral changes at this time. But it makes for really nice and sometimes fearful stories that are widely publicized."
Those sensationalistic stories also trivialize the complex reality of mental health issues, which can be influenced by a variety of physiological factors.
UCL scientists highlighted that Toxoplasma gondii can still pose a danger, however.
"Our study suggests that cat ownership during pregnancy or in early childhood does not pose a direct risk for later psychotic symptoms," senior author Dr. James Kirkbride said in a statement. "However, there is good evidence that Toxoplasma gondii exposure during pregnancy can lead to serious birth defects and other health problems in children." The parasite can also cause serious health problems in people with compromised immune systems, according to the Centers for Disease Control and Prevention.
To properly address the risks of Toxoplasma gondii, it's important to know how the parasite is actually transmitted, which is a little more complicated than some media reports suggest.
For cats to have the parasite in their systems, they first must eat contaminated raw meat or an infected rodent — which means that keeping your cat indoors goes a long way toward preventing an infection. Once cats are infected, they are able to shed the parasite for two weeks afterwards. People can then contract it from accidentally ingesting the cat's feces or materials that have come into contact with them, according to the CDC.
The CDC recommends that pregnant women avoid changing cat litter if possible. But if that's not possible, it urges them to wear disposable gloves and thoroughly wash their hands afterwards. It also recommends washing fruits and vegetables, wearing gloves while gardening or handling soil, and making sure to take food safety precautions.