The study, published in the American Journal of Preventive Medicine, showed that the risk of suffering from coronary heart disease was 1.9 times higher for women living in poor areas than for women from rich neighbourhoods. The risk for men in poor areas was 1.5 times higher.
The higher incidence of heart disease was independent of factors such as age, marital status, family income, educational attainment, immigration status and mobility.
The authors of the study said that even when higher incidence of obesity, diabetes, smoking and high blood pressure in deprived neigbourhoods were taken into account, the incidence of heart disease was still higher than in high-income areas.
“We know that there is a neighbourhood effect, but we don’t know what it is that makes people ill,” said Kristina Sundquist, one of the authors of the study, to The Local.
The study, led from Stanford University and involving researchers from UC-San Francisco, analysed data from the whole Swedish population aged between 35 and 74. The researchers followed each individual from 1996 to 2000, noting incidence of coronary heart disease and comparing this to the neighbourhood the person lived in.
The findings have so far baffled researchers, who are unable to find a simple explanation for the large differences between rich and poor areas.
“Previous studies in the United States have shown that poorer neighbourhoods have more liquor stores, but that does not apply in Sweden,” said Sundquist, referring to Sweden’s limited number of state-controlled liquor stores.
Poor exercise facilities or built environments that discourage walking could also be factors.
Other theories that could explain the difference is higher levels of depression and psychological stress in poorer areas.
“Previous studies have shown that depression affects coronary heart disease,” said Sundquist.
Higher levels of chronic infections in areas with more crowded living conditions could also play a role, Sundquist said.
Another factor that could be significant is the difficulty in retaining staff in primary care centres in poorer areas, with better access to medical care for those who live in better-off neighbourhoods.
Sundquist said it was possible that the differences between rich and poor areas could be even greater in other countries with more uneven income distribution than Sweden.
“I would expect the differences to be larger in a country such as the United States, but this is not certain.”