Cats got a reprieve of sorts this week. A new study has found no link between being raised in a household with cats and developing a psychiatric disorder later in life.
The study’s findings challenge previous research that has suggested cat ownership may play a role in some psychiatric illnesses, particularly schizophrenia.
For example, in 2012, a meta-analysis (an analytic review) of 38 studies found that people with schizophrenia were almost three times more likely to test positive for antibodies to a common infectious parasite known as Toxoplasma gondii. (When antibodies to a particular infectious agent are present in the blood, it’s a sign that the person has been previously exposed to that agent.)
Cats are the primary hosts of T. gondii, and the parasite can be passed on to humans through contact with cat feces — such as when changing a litter box. As a result, some researchers have suggested that children raised in households with cats may be at increased risk of developing schizophrenia and perhaps other psychiatric disorders later in life.
Those previous studies had many methodological problems, however, such as involving only a small number of people or failing to adequately account for alternative factors that may have explained the correlation between cat ownership and an increased risk of mental illness.
More rigorous approach
The authors of the new study — a team of researchers from University College London (UCL) — decided to take a more rigorous approach to the topic. They examined data collected on almost 5,000 participants in the Avon Longitudinal Study of Parents and Children, a “birth cohort” study that has been following the health of more than 14,000 children since their birth in the United Kingdom in 1991 and 1992.
The UCL researchers used data that followed the children up until the age of 18. It included the results of periodic mental health evaluations, as well as information on whether the children’s homes had cats, either when the mother was pregnant or when the children were growing up.
After analyzing all that data, the UCL researchers concluded that exposure to house cats during gestation or childhood was not associated with psychotic symptoms during adolescence — symptoms such has hallucinations or delusions of being persecuted or spied on, which can be early signs of mental illness.
“The message for cat owners is clear: there is no evidence that cats pose a risk to children’s mental health,” said Francesca Solmi, the study’s lead author and an psychiatric epidemiologist at UCL, in a released statement. “In our study, initial unadjusted analyses suggested a small link between cat ownership and psychotic symptoms at age 13, but this turned out to be due to other factors. Once we controlled for factors such as household over-crowding and socioeconomic status, the data showed that cats were not to blame.”
“Previous studies reporting links between cat ownership and psychosis simply failed to adequately control for other possible explanations,” she added.
A caveat — and a warning
This study has its own limitations, of course. Most notably, it didn’t include blood tests of the participants to see if they had been directly exposed to T. gondii. How many of the children in the study who grew up with cats were actually exposed to the infection is therefore unknown.
Still, this study appears to be the best evidence we have to date on the subject — and the findings will be reassuring to cat owners.
Pregnant women, however, should continue to take care to avoid exposure to T. gondii, stress the study’s authors. That means staying away from litter boxes and other areas (like loose soil in the garden) where their cat — or neighborhood cats — may have deposited contaminated feces.
“Our study suggests that cat ownership during pregnancy or in early childhood does not pose a direct risk for later psychotic symptoms,” explained James Kirkbride, the study’s senior author and a psychiatric epidemiologist at UCL, in the released statement. “However, there is good evidence that T. Gondii exposure during pregnancy can lead to serious birth defects and other health problems in children.”
“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 added.