A new study in the Journal of Occupational and Environmental Medicine suggests that minimum-wage employees are more likely to be obese than those who earn higher wages, adding to growing evidence that being poor is a risk factor for unhealthy weight.

The authors say the study provides justification for raising minimum wage rates around the country which would allow low-income workers to make healthier choices.

"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 say this may be because 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.

For the study, researchers used a novel 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."


Citation: DaeHwan Kim, John Paul Leigh, 'Estimating the Effects of Wages on Obesity', Journal of Occupational and Environmental Medicine, 2010, 52(5), 495; doi: 10.1097/JOM.0b013e3181dbc867