Exposure to household pet cats and dogs in childhood and risk of subsequent diagnosis of schizophrenia or bipolar disorder

Cat Ownership and Schizophrenia-Related Disorders and Psychotic-Like Experiences: A Systematic Review and Meta-Analysis

BACKGROUND

It has been proposed that cat ownership may be a risk-modifying factor for schizophrenia-related disorders and psychotic-like experiences (PLE). This study aimed to systematically review and meta-analyze publications that reported the relationship between cat ownership and schizophrenia-related outcomes.

METHODOLOGY

We searched Medline, Embase, CINAHL, Web of Science, and gray literature for publications between January 1, 1980, and May 30, 2023, regardless of geographical location and language. Backward citation search methods were used to locate additional articles. We included studies that reported original data on cat ownership and schizophrenia-related outcomes. We meta-analyzed estimates based on broad definitions (cat ownership, cat bites, and cat contact) with estimates with or without covariate adjustments. We pooled comparable estimates using random-effects models and assessed the risk of bias, heterogeneity, and study quality.

RESULTS

We identified 1915 studies, of which 106 were chosen for full-text review, ultimately resulting in the inclusion of 17 studies. We found an association between broadly defined cat ownership and increased odds of developing schizophrenia-related disorders. For the studies reporting unadjusted odds ratios (OR; n = 10), the pooled OR was 2.14 (95% CI: 1.29-3.55). Exclusion of one outlier study resulted in a pooled OR (n = 9) of 1.56 (95% CI: 1.27-1.92). For the studies reporting adjusted estimates (n = 5), the pooled OR was 2.44 (95% CI: 1.59-3.73). After excluding one study with suboptimal exposure/design features, the pooled adjusted OR (n = 4) was 2.40 (95% CI: 1.50-3.86). We were unable to aggregate the estimates for the PLE outcomes because of the broad range of measures.

CONCLUSIONS

Our findings provide support for the hypothesis that cat exposure is associated with an increased risk of broadly defined schizophrenia-related disorders; however, the findings related to PLE as an outcome are mixed. There is a need for more high-quality studies in this field.

PROSPERO REGISTRATION

PROSPERO 2023 CRD42023426974. Available from: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42023426974.

Conditional associations between childhood cat ownership and psychotic experiences in adulthood: A retrospective study

Ownership of cats in childhood has been inconsistently associated with psychosis in adulthood. Parasitic exposure, the putative mechanism of this association, may be more common with rodent-hunting cats, and its association with psychosis may depend on other environmental exposures. We examined the conditional associations between childhood cat ownership and the frequency of psychotic experiences in adulthood. Adults (n = 2206) were recruited in downtown Montreal to complete a survey about childhood cat ownership (non-hunting or rodent-hunting), winter birth, residential moves in childhood, head trauma history, and tobacco smoking. The frequency of psychotic experiences (PE) was measured with the 15-item positive subscale of the Community Assessment of Psychic Experiences. Associations between exposures and PE were examined in linear regressions adjusted for age and sex. Interactions among variables were explored using a conditional inference tree. Rodent-hunting cat ownership was associated with higher PE scores in male participants (vs. non-hunting or no cat ownership: SMD = 0.57; 95% CI: 0.27, 0.86), but not in female participants (SMD = 0.10; 95% CI: -0.18, 0.38). In the conditional inference tree, the highest mean PE score was in the class comprised of non-smokers with >1 residential move, head trauma history, and rodent-hunting cat ownership (n = 22; mean standard score = 0.96). The interaction between rodent-hunting cat ownership and head trauma history was supported by a post-hoc linear regression model. Our findings suggest childhood cat ownership has conditional associations with psychotic experiences in adulthood.

Early Exposure to Animals and Childhood Body Mass Index Percentile and Percentage Fat Mass

INTRODUCTION

A few studies have identified childhood animal exposure as associated with adiposity, but results are inconsistent and differ in timing.

METHODS

We conducted an observational cohort study of children ages 4-8 in the Environmental Influences on Child Health Outcomes [ECHO] study. The main exposure was having a dog in the home and/or regular contact with farm animals during the first year of life. Outcomes of interest were child BMI percentile (adjusted for gender and age) categorized as normal/underweight (<85^th percentile), overweight (85^th to <95^th), and obese (≥95^th), and percent fat mass (continuous). Associations were analyzed using multinomial logistic regression and multivariable linear regression, respectively, with and without multiple imputation.

RESULTS

First year animal exposure occurred in 245 of 770 (31.8%) children. Children with early animal exposure had 0.53 (95% CI: 0.28, 0.997) times the odds of being in the obese BMI category compared to those exposed to animals after controlling for covariates: maternal pre-pregnancy BMI, race/ethnicity, reported child activity level, receiving food assistance, age child began daycare (<1 year vs 1+), exclusively breastfed x6 months, and NICU admission (n=721). Children with early animal exposure had, on average, 1.5% (95% CI: -3.0, -0.1) less fat mass than exposed children after adjustment for maternal BMI, race/ethnicity, activity, food assistance, breastfeeding, and maternal education (n=548). Multiple imputation did not alter either result.

CONCLUSION

These results provide evidence that exposure to dogs or farm animals in the first year of life is associated with lower odds of obesity and lower percent fat mass in childhood.

Pet Ownership and Quality of Life: A Systematic Review of the Literature

Pet ownership is the most common form of human–animal interaction, and anecdotally, pet ownership can lead to improved physical and mental health for owners. However, scant research is available validating these claims. This study aimed to review the recent peer reviewed literature to better describe the body of knowledge surrounding the relationship between pet ownership and mental health. A literature search was conducted in May 2020 using two databases to identify articles that met inclusion/exclusion criteria. After title review, abstract review, and then full article review, 54 articles were included in the final analysis. Of the 54 studies, 18 were conducted in the general population, 15 were conducted in an older adult population, eight were conducted in children and adolescents, nine focused on people with chronic disease, and four examined a specific unique population. Forty-one of the studies were cross-sectional, 11 were prospective longitudinal cohorts, and two were other study designs. For each of the articles, the impact of pet ownership on the mental health of owners was divided into four categories: positive impact (n = 17), mixed impact (n = 19), no impact (n = 13), and negative impact (n = 5). Among the reviewed articles, there was much variation in population studied and study design, and these differences make direct comparison challenging. However, when focusing on the impact of pet ownership on mental health, the results were variable and not wholly supportive of the benefit of pets on mental health. Future research should use more consistent methods across broader populations and the development of a pet-ownership survey module for use in broad, population surveys would afford a better description of the true relationship of pet ownership and mental health.

Demographic and contextual factors as moderators of the relationship between pet ownership and health

OBJECTIVE

Companion animals are an important feature of the family system, and human-animal interaction is increasingly being recognized as an important social determinant of health. However, there is a need for more nuanced assessment of not only who owns pets, but how pet ownership is related to various health outcomes, and which sociodemographic and contextual factors moderate these associations.

DESIGN

Secondary analysis of cross-sectional data collected from an online, probability-based panel to generate a nationally representative sample of adults in the United States (n = 1267). Data were analyzed using hierarchical and logistic regression models.

RESULTS

Results suggested that pet owners are systematically different from non-pet owners on a number of key demographic and contextual characteristics, and these differences vary somewhat when looking at dog owners and cat owners. When controlling for individual and family-level covariates, pet ownership was not associated with overall health status or Body Mass Index, but dog ownership was associated with higher levels of physical activity. Pet ownership was associated with higher odds of having an anxiety disorder with gender moderating this relationship, but this association was not present for dog or cat owners, suggesting this relationship is limited to other types of pets. Higher odds of depression were associated with pet ownership (for both dog and cat owners), with employment status significantly moderating the relationship between dog ownership status and depression.

CONCLUSIONS

These findings suggest that pet ownership is a complex and context specific phenomenon. Future research should carefully consider and control for sociodemographic predictors and use measurement and analysis approaches sensitive to the variations in human-animal relationships to fully understand how pets contribute to individual and family health and well-being.