Poverty is often cited as contributing to poor health. Now, in an unusual approach, researchers have calculated how many people poverty kills and presented their findings, along with an argument that social factors can cause death the same way that behavior like smoking cigarettes does.

In an article published online for the June 16 issue of The American Journal of Public Health, scientists calculated the number of deaths attributable to each of six social factors, including low income.

To estimate the number of deaths caused by each factor, the scientists reviewed 47 earlier studies on the subject, combining the data in a meta-analysis. The studies were generally based on large national surveys like the National Health and Nutrition Examination Survey, a continuing study by the Centers for Disease Control and Prevention.

Then, using the pooled data, the researchers calculated the “population-attributable fraction” of deaths — that is, the number of deaths caused by living with a given social disadvantage.

Finally, they multiplied that fraction by the total number of deaths in the year 2000 to come up with a number of deaths caused by each of the six social conditions. The researchers then separated the contribution of each social factor.

“The methods we’re using are limited,” Dr. Sandro Galea, the lead author, acknowledged. “Any time you try to say that death is attributable to a single cause, there’s a problem — all deaths are attributable to many causes. But what we did is just as valid as what was done to establish smoking as a cause of death.”
“This is a very interesting paper,” said Roger T. Anderson, a professor of public health sciences at Pennsylvania State College of Medicine who was not involved in the study. “It’s simple and elegant, a very straightforward approach to looking at these kinds of data.

“It brings to the surface what the impact of social disadvantage is in terms of numbers of deaths, and the authors have done a very nice job of laying out the argument.”

The researchers used various criteria to define an adverse social condition. Low education, for example, was defined as not having graduated from high school. Poverty was defined as a household income of less than $10,000. A population in which more than 25 percent of people reported their race or ethnicity as non-Hispanic black was considered racially segregated.

The study also calculated the effect of an area’s overall poverty level, income differential and low social support.

For 2000, the study attributed 176,000 deaths to racial segregation and 133,000 to individual poverty. The numbers are substantial. For example, looking at direct causes of death, 119,000 people in the United States die from accidents each year, and 156,000 from lung cancer.

Social factors are not the same as diseases or accidents, but Dr. Galea argues that they are equivalent to a behaviors like smoking, and that, as with smoking, there is evidence of the mechanism involved. He said that the causal chain between, for example, poverty and death from heart disease has many well-established links.
Dr. Galea also said that poverty results in poor access to health screening, poor access to quality care for those who actually have heart disease, greater vulnerability to stresses associated with heart disease and a greater likelihood of engaging in unhealthy behavior.

“In some ways,” Dr. Galea added, “the question is not ‘Why should we think of poverty as a cause of death?’ but rather ‘Why should we not think of poverty as a cause of death?’ ”

If they had not smoked, 400,000 people each year would not have died, Dr. Galea said. Similarly, he said, if they had graduated from high school, the 245,000 people whose cause of death he attributes to low education would still be alive.

“This might be a useful lens to help focus our minds,” said Dr. Galea, who is the chairman of the department of epidemiology at the Mailman School of Public Health at Columbia University. “If you say that 193,000 deaths are due to heart attack, then heart attack matters. If you say 300,000 deaths are due to obesity, then obesity matters.

“Well, if 291,000 deaths are due to poverty and income inequality, then those things matter too.”