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17-01-2013 | Cardiology | Article

Tree decline linked to cardiac and respiratory deaths

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medwireNews: The spread of an infectious borer that has killed millions of trees in the USA is associated with greater risk for respiratory and cardiovascular mortality among local residents, say researchers.

Geoffrey Donovan (Pacific Northwest Research Station, Portland, Oregon, USA) and colleagues collected data from 1296 counties in 15 states affected by the emerald ash borer, Agrilus planipennis, between 1990 and 2007. Because the ash borer was first reported in the USA in 2002, this allowed them to compare mortality before and after the infestation.

As reported in the American Journal of Preventive Medicine, the authors found that the borer was significantly associated with increased rates of lower respiratory tract disease mortality in adults, leading to an additional 6.8 additional deaths per year per 100,000 adults within a given county. Applying their estimates to all counties in the study, the authors estimate that the emerald ash borer infestation may have led to 6113 excess deaths between 2002 and 2007.

Similar associations were found for cardiovascular-related mortality, and the authors estimate that 16.7 additional deaths per year per 100,000 adults are attributable to the borer's presence in a county. This translates to a total of 15,080 excess deaths between 2002 and 2007 across all counties, they report.

For both types of mortality studied, the authors found that the borer had a greater impact in wealthier areas. They suggest that this could be because wealthier areas have greater tree coverage to begin with.

Donovan and colleagues say that the spread of the borer gave them a unique opportunity to assess a "natural experiment" into the effects of the environment on human health. Many previous studies have been cross-sectional in design and failed to account for confounding factors, but the authors say that theirs comes closer to a randomized study.

Proposed links between tree density and cardiovascular and respiratory health include air quality, stress reduction, physical activity, and moderating temperature. However, the authors conclude that further research will be needed to clarify the mechanisms that connect the natural environment to human health.

By Kirsty Oswald, medwireNews Reporter

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