Rat study shows stress worsens air pollution health effects.
Clougherty, JE, CA Rossi, J Lawrence, MD Long, EA Diaz, R Lim, B McEwen, P Koutrakis and JJ Godleski. 2010. Chronic social stress and susceptibility to concentrated ambient fine particles in rats. Environmental Health Perspectives http://dx.doi.org/10.1289/ehp.0901631.
Two distinct exposures – one environmental and one social – can act on rats to significantly alter the immune system and increase respiratory problems where one of them alone would not, researchers report. The animal study found that higher exposures to traffic-related air pollution were associated with a rapid, shallow breathing pattern only among chronically stressed rats.
This is the first toxicological study to examine how chronic stress modifies the effect of fine particle air pollution on respiratory function. The findings suggest that changes in the immune and inflammatory responses of stressed rats may play a role in making them more susceptible to effects of air pollution.
The results are consistent with human studies that report stronger health effects of air pollution among those who experience higher levels of social stressors, such as exposure to violence. This work may shed insight on existing health disparities since lower income populations often experience higher levels of environmental exposures and social stressors.
Researchers randomly assigned 24 male rats to four different groups (stress/air pollution; stress/clean air; no stress/air pollution; no stress/clean air). Chronic stress was simulated by placing individual rats into a dominant male’s home cage twice a week for a total of 16 stress exposures. After each stress exposure, rats were exposed to urban air pollution particles – about 30 times the concentration normally found in outdoor air – for 5 hours a day for 10 days. Their breathing patterns were determined with special instruments and immune and inflammation markers were measured in the rats' blood.
The stressed rats that were breathing polluted air had higher levels of C-Reactive Proteins (CRP) – a protein that increases in response to inflammation – and white blood cells than non-stressed rats. While variable, their breathing was significantly altered, generally more rapid and shallow. These changes were not seen in rats that were exposed to only air pollution or just stress.
While this study had a small sample size and no distinction among chronic and acute stress, the results suggest stress may worsen some of the health effects associated with breathing traffic-related air pollution. Future studies could address these limitations, the authors propose.
