A recent theme in epidemiology and health geography is understanding how social inequality impacts health outcomes (for a review see Richard Wilkinson‘s popular science book Impact of Inequality : How to Make Sick Societies Healthier).

Scientific American.com reports on health geography research that shows that:

Poor people die sooner when living in higher-income neighborhoods than in poorer ones, a new report concludes. Researchers analyzed 17 years’ worth of data on thousands of people from four mid-size northern California cities to determine the death rates among different socioeconomic groups residing in the same neighborhoods. Higher rents or property taxes and limited access to free services may explain the paradoxical outcome for poor people with better-off neighbors.

Epidemiologists have found that neighborhood plays a key role in predicting an individual’s health, with people in high-income communities tending to fare better than those living elsewhere. Prior studies hinted that poorer residents of well-to-do areas are excluded from those benefits and may even fare worse than counterparts in poorer areas, but these analyses didn’t control for risk factors such as smoking and physical activity. Taking up the topic, Marilyn Winkleby of Stanford University and her colleagues looked at data on 8,200 men and women in 82 neighborhoods, originally collected for a study of heart disease risk factors between 1979 and 1990. The researchers assigned each individual and neighborhood to a socioeconomic group–low, moderate or high–based on income and education.

The result held. In neighborhoods with a top median income of $47,000, 19 of every 1,000 poor women had died after 17 years, compared with 11 per 1,000 in neighborhoods that had a top median income of $38,600; men fared similarly. Both groups tended to die from the same chronic diseases, and the pattern remained even after accounting for age, obesity, blood pressure and smoking status, the group reports in a paper to be published in the December American Journal of Public Health. The finding could not be explained by nearness to negative or positive health influences, such as bars, fast-food outlets, physicians, grocery stores, parks or gyms, Winkleby says.

The researchers cite two possible explanations: Economically, those of modest means living in a well-off neighborhood may have less to spend on health care and nutritious food after paying rent or property taxes. “You might be right next door to a pharmacy but not have money for medications,” Winkleby observes. Poorer residents may also be missing out on free social services found in low income neighborhoods. Psychologically, perceiving a discrepancy in social status can cause stress that may affect health, the researchers note. “The people in well-to-do neighborhoods should recognize that there’s a population that may be high risk and sort of hidden,” Winkleby says. “It’s clearly a more powerful analysis than what has been done previously,” says epidemiologist Paul Veugelers of the University of Alberta. “It’s pretty strong.” The effect is less pronounced in Canada, which has a bigger public health system, he notes, suggesting that financial access to health care indeed contributes to the death rate of low-income people living in better-off areas. Finding the precise risk factors will require looking at changes in health prior to death, he adds.