Researchers have found no correlation between growing up with a cat and developing mental illness.

Cats often carry Toxoplasma gondii, a parasite that can cause infections in humans and can lead to later psychosis in those who have been infected. For that reason, some research has suggested that cat ownership could increase the chance of developing mental illness. However, a new longitudinal study done by researchers at the University College London found limited evidence to support this hypothesis. The study was published online in Feb. 2017 in Psychological Medicine.

Using birth cohort data from the Avon Longitudinal Study of Parents and Children (ALSPC), researchers aimed to investigate whether cat ownership in pregnancy or childhood was associated with psychotic experiences in early and late adolescence. The ALSPAC looked for women expected to deliver between April 1991 and April 1992, enrolling 14,541 women. Women reported information on pet ownership during pregnancy, and when their children were 8, 21, 31, and 47 months old. Children were then brought in for clinic visits at ages 13 and 18 years old for interviews.

From this information, researchers looked at two exposure variables: whether the mother owned a cat during pregnancy and whether she owned one when the child was four years old. As a secondary exposure, they also looked at whether they owned a cat when the child was 10 years old.

Study analyses were based on participants who had complete data at ages 13 (6,705 children) and 18 (4,676 children). In both samples, around one third of mothers had owned a cat during pregnancy, and when the child was four and 10 years old.

When taking a univariable approach (cat ownership), there seemed to be a higher risk associated, but once multivariable factors were considered (i.e. housing type; household crowding; maternal education, social class, and marital status; paternal age; number of house moves), that effect was no longer significant. So, while owning a cat at four years old was associated with higher odds of having psychotic symptoms at 13 with the univariable models, it was not with the multivariable adjustment.

These findings are not consistent with other studies, and the researchers suggest this is due to methodological differences. According to the study, other investigations “have generally been hindered by notable methodological limitations, including reliance on case-control designs that are susceptible to recall bias, small ad hoc samples and weak statistical analyses, which have failed to adequately account for confounding or missing data.”

They concluded that while good evidence supports an association between a T. gondii infection and later psychosis, cat ownership in pregnancy or early childhood does not also seem to be a risk factor. Despite this lack of correlation, researchers do still advise pregnant women avoid handling soiled cat litter due to the risk of acquiring a T. gondii infection.

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