Is there really a link between owning a cat and mental illness?

Francesca Solmi, UCL and James Kirkbride, UCL

Over the past few years, cats have increasingly attracted media attention due to a number of scientific studies reporting that a Toxoplasma Gondii (T. Gondii) infection is linked with mental health issues, including schizophrenia, suicide and intermittent rage disorder. Since domestic cats are the primary hosts of T. Gondii – that is, they provide an environment within which this parasite can reproduce – it is often speculated that cat ownership may put people at increased risk of mental illness, by exposing them to it.

However, only a handful of small studies have found evidence to support a link between owning a cat and psychotic disorders, such as schizophrenia. And most of these investigations have serious limitations. For instance, 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. This can often lead to results that are born out of chance or are biased.

To tackle these limitations, we conducted a study using data from approximately 5,000 children who took part in the Avon Longitudinal Study of Parents and Children between 1991 and 1992. Since then, these children and their families have been followed up to gather information on their health, as well as on their demographic, social and economic circumstances.

So, unlike previous studies, we were able to follow people over time, from birth to late adolescence, and address a number of the limitations of previous research, including controlling for alternative explanations (such as income, occupation, ethnicity, other pet ownership and over-crowding) and taking into account missing data.

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.

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. This finding in a large, representative sample did not change when we used statistical techniques to account for missing data and alternative explanations. This means that it is unlikely that our results are explained by chance or are biased.

While this finding is reassuring, there is evidence linking exposure to T. Gondii in pregnancy to a risk of miscarriage and stillbirth, or health problems in the baby. In our study, we could not directly measure exposure to T. Gondii, so we recommend that pregnant women should continue to avoid handling soiled cat litter and other sources of T. Gondii infection, such as raw or undercooked meats, or unwashed fruit and vegetables. That said, data from our study suggests that owning a cat during pregnancy or in early childhood does not pose a direct risk for offspring having psychotic symptoms later in life.

Francesca Solmi, Research Associate, UCL and James Kirkbride, Reader, UCL