Linking air pollution to body weight and obesity

About

The proportion of the global population that could be classified as overweight and/or obese has increased substantially over recent decades. Body weight conditions like overweight and obesity have been identified as risk factors for a variety of chronic diseases, including diabetes, cardiovascular and kidney diseases, and some cancers. In 2018 the World Health Organization estimated that overweight and obesity lead to at least 2.8 million deaths and 35.8 million disability-adjusted life years annually across the world. In response to this epidemic, numerous economics studies have sought to understand the complex and varied causes of obesity.

One potential cause is air pollution, which can affect body weight through biological channels (e.g., slowing down the metabolism) and behavioral channels (e.g., reducing exercise and increasing calorie intake). Previous health science studies have suggested multiple potential pathways between air pollution exposure and body weight, but identifying the causal effect is challenging: air pollution is a byproduct of economic activity, and thus potentially correlated with economic confounders, such as income and food prices, which are also important determinants of obesity. We provide the first attempt at estimating the causal link between ambient air pollution, and particularly, fine particulate matter (PM2.5) and obesity, with a geographic focus on China. 

Approach

We used data on body weight and height from the China Health and Nutrition Survey (CHNS), which is the longest and most comprehensive health survey in China. The CHNS provided detailed information on health and nutrition along with socioeconomic and demographic data for 13,741 adult individuals (aged 18 or older) from eight provinces in China over the period of 1989–2015. We then matched the CHNS data with satellite-based pollution and thermal inversions (air pollution conditions that are typically independent of economic activities) data by county of residence and month of the interview for each interviewee. We then study the effect of pollution on behavioral responses including physical and sedentary activities, sleeping, transportation mode, and calorie intake.

Key Findings

We found a positive and statistically significant effect of PM2.5 on body weight. Specifically, a 1.54% increase in average PM2.5 concentrations in the past 12 months increases BMI (body mass index) by 0.27%, and increases the overweight and obesity rates by 0.82 and 0.27 percentage points, respectively. The dynamics of exposure to air pollution matter: we did not detect significant short-run effects coming from exposure to air pollution in the first three months following an interview. We also found that air pollution reduces physical activity, the probability of walking to work or school, sleeping time, and increases fat intake. This suggests that behavioral channels play an important role in the pollution-obesity relationship.

Partners

This study was a collaboration with Dr. Huixia Wang and Dr. Si Wang at Hunan University as well as Dr. Peng Zhang at The Chinese University of Hong Kong.