Previous research results suggesting that people who grow up with cats are at higher risk of mental illness have been cast in doubt, as new research done at UCL finds that there is no link between cat ownership and psychotic symptoms.

Cats are the primary host of the common parasite Toxoplasma Gondii (T. Gondii), which is known to contribute to mental health problems such as schizophrenia. The previous research suggested that cat ownership might therefore contribute to some mental disorders. In an article published in Psychological Medicine, the new study suggests that owning a cat during childhood and pregnancy plays no role in developing psychotic symptoms during adolescence.

Looking at nearly 5000 people born in 1991 or 1992 who were followed up until the age of 18, the study found no link between cat ownership and psychotic symptoms. The research team knew whether the household had cats while the mother was pregnant, or while the children were growing up.

Dr Francesca Solmi from the UCL Psychiatry department and lead author of the paper emphasized that cat owners need not be concerned, as there is no evidence that points to cats posing a risk to children’s mental health. She also explained that although initial unadjusted analyses suggested a tiny possible link between psychotic symptoms and cat ownership at age 13, this turned out to be due to other factors. Once factors such as socioeconomic status and household over-crowding were however controlled for, the data showed that cats did not cause the symptoms. Previous studies demonstrating links between psychosis and cat ownership simply neglected to control for other possible explanations adequately.

The new study was considerably more reliable than previous research in this area as the team studied families that were followed up frequently for almost 20 years. This method is much more reliable than those used in previous studies are, where people with and without mental health problems were asked to remember details about their childhood. Such accounts are more prone to errors in recall, which can in turn lead to unreliable findings.

While the new study looked at a large population and was able to account for missing data, the previous studies had significant gaps in the data and were relatively small. Although the new study did not measure T. Gondii exposure directly, the data suggest that cat ownership does not significantly increase exposure if the parasite does indeed cause psychiatric problems.

Dr James Kirkbride from the UCL Psychiatry department and senior author of the paper explained that the results indicate that there is no direct risk for later psychotic symptoms if cats are owned during pregnancy, or in early childhood. There is however some evidence that T. Gondii exposure during pregnancy can lead to serious birth defects and other health problems in children. As such, pregnant women should not handle soiled cat litter in case it contains T. Gondii.