National happiness is influenced by complex relationships beyond basic economic factors, according to a study by Javier I. Borráz-León of the Secretariat of Science, Humanities, Technology, and Innovation in Mexico City and colleagues.

Published Sept. 30, 2026, in the journal PLOS One, the study finds that cats and their parasites are strongly correlated with both positive and negative happiness scores worldwide.

The general well-being of a country's populace is often represented by a national happiness score. Such scores are known to be associated with economic factors such as family income and health costs, but other factors have rarely been explored. In this study, researchers investigated the nuanced relationships underlying national well-being by factoring in the presence of domestic cats and their parasites.

The team compiled data from 93 countries, including income, health costs, GDP, domestic cat density and the prevalence of Toxoplasma, a parasite that can be transferred from cats to humans.

The data revealed that greater numbers of cats are associated with higher national happiness—consistent with studies on the benefits of pet ownership—but also that greater Toxoplasma prevalence is associated with lower national happiness, despite the parasite being spread by cats. These counterintuitive results suggest complex factors at work.

This study does not resolve the underlying causes of these associations, but the authors suggest that the influence of cats on happiness might be tied to economic factors; higher income and better public health, for example, might encourage pet ownership while reducing infection rates.

This study demonstrates that biological factors as well as economic ones can correlate with happiness, revealing new avenues for investigating national well-being. The authors note that while this study unveils previously unrecognized relationships, future studies will be needed to determine the underlying mechanisms.

The authors add, "What we found is that countries with more cats tended to report higher levels of happiness, while countries with higher exposure to Toxoplasma gondii tended to report lower levels of happiness. Of course, these are associations at the country level, so we cannot say that having more cats makes people happier or that Toxoplasma makes people less happy, but the patterns are interesting enough to deserve further investigation."

"What we find most interesting is that these results bring together factors that are usually studied separately: wealth, health, human–animal relationships and infectious disease. Our study suggests that understanding why some populations report greater well-being may require us to consider biological and ecological factors alongside the socioeconomic conditions that have traditionally received most attention"...