Obesity linked to lowest earnings

"Our study clarifies a link that has been assumed but difficult to prove," said Paul Leigh, senior author of the study and professor in the UC Davis Center for Healthcare Policy and Research. "The correlation between obesity and poverty-level wages was very strong."

Public-health scientists have identified several potential reasons why lower wages could support the tendency for obesity. One is that poorer people tend to live in less-safe neighborhoods with reduced access to parks and other low-cost means of physical activity. Healthy, lower-calorie foods also tend to be more expensive and less available in poorer communities. California's Obesity Prevention Plan, for instance, notes that many low-income families have less access to healthier foods and often have to travel greater distances than others to find healthier food options at lower prices.

"The outcome leads us to believe that raising minimum wages could be part of the solution to the obesity epidemic. Doing so could increase purchasing power enough to expand access to healthier lifestyle choices," Leigh said.

Published in the May issue of the Journal of Occupational and Environmental Medicine, the finding is the result of the novel use of a statistical technique known as instrumental variables, which is often used by economists and other social scientists to determine causal rather than coincidental relationships between, for instance, education and earnings.

"Instrumental variables gave us the chance to evaluate an independent factor that is definitely not caused by obesity -- minimum wages," said Leigh, who is an expert in health and labor economics. "After adjusting for inflation, minimum wages have been stagnant or falling over the past three decades, placing most full-time workers near the poverty line. It is also during those same three decades that we have seen the prevalence of obesity soar."

In gathering data to assess through instrumental variables, the team started with the Panel Study of Income Dynamics. This longitudinal, representative sample of people in the United States includes information on height and weight, which were used to calculate body mass index (BMI), in addition to demographics and earnings. The researchers isolated data collected in 2003, 2005 and 2007 from 6,312 full-time workers in over 40 states who were 20-to-65 years of age and identified themselves as heads of households. State-established minimum-wage data for those same three years was obtained from the U.S. Department of Labor.

The results showed that people earning the lowest wages were more likely to have weights in the obese range, or BMIs of 30 or greater. People living in the southern United States -- where state minimum-wage levels are among the lowest -- were more likely to be obese than people in other regions.

Leigh noted that one limitation of the study is its sample. Those identifying themselves as household heads were 85 percent men and 90 percent Caucasian.

"Future research should address wage and obesity correlations among samples that include more African-Americans, Hispanics, Asians and women," said Leigh. "Obesity is a complex problem that likely has multiple causes. The more we can pinpoint those causes for specific populations, the greater chances there are for reducing its impact."

The study was supported in part by the National Institute for Occupational Safety and Health. Leigh co-authored the study with DaeHwan Kim, who recently obtained his doctorate in economics at UC Davis and is now a research fellow at the Korea Insurance Research Institutes in Seoul.