Cats are among the most popular pets in the United States, with more than 30 percent of households owning at least one feline friend.
As well as being beloved companions, studies have shown that cats and other pets can benefit mental health, helping to reduce anxiety and stress and improve overall psychological well-being.
Some research, however, has suggested the opposite. One study reported by Medical News Today in 2015, for example, associated cat ownership in childhood with increased risk of schizophrenia, bipolar disorder, and other mental health conditions in later life.
But according to Dr. Solmi and colleagues, there is insufficient evidence to suggest this is the case.
Toxoplasma gondii and mental illness
The previously reported link between childhood cat ownership and mental health disorders has been attributed to Toxoplasma gondii, a parasite that cats shed in their feces. Coming into contact with cat feces contaminated with this parasite - through cleaning a litter tray, for example - may lead to T. gondii infection, known as toxoplasmosis.
While more than 60 million people in the U.S. are believed to be infected with T. gondii, the immune system is normally able to stave it off, meaning very few people have symptoms.
Pregnant women, however, are more susceptible to T. gondii infection, which may have serious implications for their offspring, such as birth defects. Studies have also suggested that T. gondii infection in early life may raise the risk of mental health disorders later on.
The new study, however, finds that simply growing up with a cat is unlikely to raise the risk of mental illness.
Dr. Solmi and colleagues came to their findings by analyzing data from the Avon Longitudinal Study of Parents and Children (ALSPAC), identifying 4,676 children who were born between 1991 and 1992.
Cat ownership during their mother's pregnancy and between the ages of 4-10 years was assessed, and each child underwent assessment for psychotic symptoms at the ages of 13 and 18.
'No evidence that cats pose a risk to children's mental health'
Initially, the researchers found a small link between cat ownership in childhood and psychotic symptoms at the age of 13. However, this association disappeared when the team accounted for other factors.
"Once we controlled for factors such as household overcrowding and socioeconomic status, the data showed that cats were not to blame," explains Dr. Solmi. "Previous studies reporting links between cat ownership and psychosis simply failed to adequately control for other possible explanations."
While the researchers were unable to assess the children's direct exposure to T. gondii, they say their findings suggest that cat ownership in pregnancy or childhood is not a risk factor for mental illness.
"However, there is good evidence that T. gondii exposure during pregnancy can lead to serious birth defects and other health problems in children," warns senior author Dr. James Kirkbride, also of the Division of Psychiatry at UCL.
"As such, we recommend that pregnant women should continue to follow advice not to handle soiled cat litter in case it contains T. gondii," he adds.
Additionally, the team says previous studies were relatively small, had missing data, and did not follow families for long periods. This new study addressed these shortfalls.