Impact of pet ownership in early childhood at ages 1 and 4-5 years on mental health at ages 7-8: findings from the INMA project.

Background: We aimed to explore associations between the presence of pets at one and 4-5 years of age with internalizing and externalizing problems at 7-8 years.

Methods: Participants comprised 1893 families from the INfancia y Medio Ambiente (INMA) project. Information was collected on the presence of (1) any pet, (2) dogs, (3) cats, (4) birds or (5) other animals. Pet ownership was categorized as never, always, only at age 1 and only at age 4-5. Internalizing and externalizing problems were measured at ages 7-8 years through the Strengths and Difficulties Questionnaire, a Likert questionnaire on children's behavioural and emotional symptoms. Negative binomial regression models and Tukey's multiple comparison tests were used to analyse data sets. Five sensitivity analyses were performed.

Results: Families that always owned a pet made up 24.4% of the sample. In addition, 11.5%, 4.5%, 3.8% and 17.6% of the families owned a dog, cat, bird or other animal, respectively. The median (P25-P75) for internalizing problems was 3 (1-5) and 5 (3-8) for externalizing problems. Owning a cat only at age 4-5 increased mental health problems: relative rate ratio (RRR) [95% confidence interval (CI)] 1.37 (1.05-1.79) for internalizing and 1.26 (1.02-1.56) for externalizing. Always having other animals was a protective factor for internalizing problems with an RRR of 0.80 (0.66-0.96). These associations remained after multiple comparison testing and sensitivity analyses.

Conclusion: Owning a cat only at 4-5 years of age was linked to more internalizing and externalizing problems, whereas always having other animals was a protective factor against internalizing problems.