Study Finds Correlation Between Income, Mortality

Income inequality has a significant correlation with mortality rates in the United States, according to a recent study by researchers at the Harvard School of Public Health.

The study found that a one percent increase in the Robin Hood Index, used to measure income inequality, was associated with an increase in the total mortality rate of 21 deaths per 100,000 people.

Researchers used 1990 Census data and mortality data from the National Center for Health Statistics to demonstrate, for the first time, the relationship between income inequality and death from coronary heart disease, cancer and homicide.

In addition, they found that for treatable diseases such as tuberculosis, pneumonia or hypertension, the mortality rate was higher in states where the income gap was wider.

"A startling finding was that our measure of income inequality explained more than 50 percent of the difference in homicide rates between states," said Bruce P. Kennedy, director of public health practice and lead author of the study.

"This lends support to the hypothesis that community breakdown or 'normlessness' are trends in our society that must be addressed before societal violence can be countered," Kennedy said.

The study, which appeared in the April 20 British Medical Journal, found that the income gap was widest in the South. As hypothesized, the mortality rates for all causes of death and certain diseases were also highest in the South.

New Hampshire, Hawaii and Utah were among states where income distribution was most equitable, according to the study.

In the U.S., the age-adjusted mortality rate is approximately 850 deaths per 100,000 people each year. The authors estimated that if the U.S. could achieve a modest reduction in the size of the income gap to make it comparable with the United Kingdom, overall death rates could be reduced by seven percent and deaths from coronary heart disease by 25 percent.

"This aggregate analysis gives us a sense that the growing gap in incomes is neither just a political nor economic problem--it's a significant public health problem," said Ichiro Kawachi, assistant professor of health and social behavior and a co-author of the study.

"The so-called Robin Hood measure of income inequality has never before been applied to health until this study," he said.

"Rather than looking at poverty per se, we were particularly interested in whether health status is affected by the relative wealth or deprivation in a population," Kawachi said. "We also looked at racial differences to see if mortality were influenced by race. We found that the problem of shortened lives, because of income inequality, potentially affects all U.S. citizens, not just the poor or historically undeserved groups such as African Americans."

The researchers concluded that higher mortality rates in areas of income inequality may reflect societal conditions in those areas.

"The effects of income inequality on health may reflect a breakdown of social cohesion, leading to increased levels of stress and frustration," Kennedy said. "Societies that tolerate large income inequalities may also underinvest in education and health care for the less well-off."

Kennedy said further studies on this topic could address whether income redistribution may improve overall health of the population.

"Further studies of communities or individuals could determine whether income inequality alone leads to premature death in different groups and also whether policies that would alter the income distribution could positively affect health for all citizens," he said.