Rich and fat? Isolating the causal effect of obesity on income among Chinese rural residents by Mendelian randomization

Purpose While the adverse health consequences of obesity are well-documented, the causal effect between obesity and economic outcomes, particularly individual income in the labor market, has yielded inconsistent findings. At the same time, China has the highest number of obese or overweight people around the world in recent years. However, limited research has examined the causal effect of obesity on Chinese rural residents’ income. To answer this question, our study aims to identify the causal impact of obesity on Chinese rural residents. Design/methodology/approach First, we conduct ordinary least squares, instrumental variable and Mendelian randomization methods to evaluate the impact of obesity on Chinese rural residents’ income. Then, we employ quantile regression and instrumental variable quantile regression to investigate the potential distributional impacts of obesity across various income segments. For the generality of our results, we also use 485,849 samples from the UK Biobank and the two-sample Mendelian randomization method to analyze. Findings Our one-sample Mendelian randomization analysis, based on a sample of 441 people collected from rural China in 2019 and 2021, revealed that obesity reduced residents’ annual income by 647.87 China Yuan. Results from the UK further support our findings. We also find that the adverse causal impact of obesity on income is significant in individuals within the above 50th percentile of the income distribution. Additionally, childhood obesity has a long-term adverse effect on income in adulthood. Research limitations/implications These results contribute to a more nuanced understanding of the economic costs of obesity. Weight penalties may lead to a deviation from the efficiency that should be pursued in the labor market and widen income disparity. Originality/value We provide novel and robust instrumental variables and utilize the Mendelian randomization method to analyze the effect of obesity on Chinese rural residents.