Study: Wood Stove Smoke May Be Deadly
By Crystal Phend, Senior Staff Writer, MedPage Today
Published: January 09, 2013
Reviewed by F. Perry Wilson, MD, MSCE; Instructor of Medicine, Perelman School of Medicine at the University of Pennsylvania
Note that in this retrospective study of two Australian towns, the implementation of an air quality intervention targeting wood smoke may have reduced overall mortality, though not enough to achieve statistical significance.
Be aware that there were significant reductions in mortality among men in the town that underwent the air quality interventions.
Cutting down on air pollution from wood stoves and other biomass-fueled fires may save lives, an Australian study suggested.
In one town, wintertime deaths from cardiovascular causes fell 20% and respiratory deaths 28% in the years following a public health campaign to enforce environmental laws and replace wood-burning heaters, Fay H. Johnston, MBBS, PhD, of the University of Tasmania, Australia, and colleagues found.
Those changes reached only a nonsignificant trend, but the impact on deaths among men was significant in every category year-round, the group reported online in BMJ.
“Our findings highlight the potential for important public health gains from interventions to reduce ambient pollution from biomass smoke,” they wrote.
The study focused on wood stoves as the source of biomass smoke, but fireplaces, forest fires, burning brush, and other sources may be important sources in other communities.
Other population-based studies have shown mortality benefits from air-quality interventions, including cutting sulfur content of gasoline in Hong Kong and ban of coal for heating homes in Dublin.
Johnston's study compared daily mortality in the Tasmanian town of Launceston in the 6.5 years before and after government-funded air quality interventions were undertaken in 2001.
Wood stoves had caught on in Tasmania during the late 1980s and early 1990s and served as the primary heating source for most homes but also accounted for about 85% of the airborne particulate matter in the winter in Launceston.
“The impact on air quality was particularly severe in Launceston, which is in a river valley where both topographical and meteorological conditions limit atmospheric dispersion of air pollution,” the researchers explained.
Government education and other efforts, most notably a wood heater replacement program, cut prevalence of wood-burning stoves from 66% to 30% of households over 2001 to 2004.
Not surprisingly, air quality improved.
The mean concentration of particulate matter under 10 μm in diameter fell from 23.7 to 18.4 μg/m3 averaged annually and from 43.6 to 27.0 μg/m3 in wintertime comparing 1997-2000 to 2001-2007 (both P<0.001).
Comparing these two periods, annual all-cause mortality declined from 8.5 to 7.4 per 1,000 person years, although this 13% change didn't reach statistical significance.
Annual cardiovascular mortality likewise fell 30% from cardiovascular causes and 25% from respiratory causes, but neither reached statistical significance.
For men, the differences between pre- and post-intervention periods were significant:
11% lower all-cause mortality (95% confidence interval 3% to 19%)
18% lower cardiovascular mortality (95% CI 3% to 31%)
23% lower respiratory mortality (95% CI less than 1% to 41%)
For wintertime mortality, the combined male and female rate tended to change after the intervention from both cardiovascular (-20%, 95% CI -36% to 2%) and respiratory (-28%, 95% CI -50% to 3%) causes.
No such changes were seen in another town on the same island, Hobart, which served as a control that did nothing to improve air quality over the study period.
The researchers cautioned that the important limitation of their analysis was the relatively small study population, at 67,000 in Launceston in 2001, which reduced the statistical power and led to wide confidence intervals for the associations.
Also, despite adjustment for temperature, humidity, day of week, respiratory epidemics, and secular mortality trends, the researchers noted that it is difficult to separate the influence of secular trends in mortality from other causes.
“Adjustment for known and unknown confounding variables in observational studies is challenging,” they acknowledged.
But “given the clear and consistent difference in results between the intervention and the non-intervention populations, our findings suggest that the improved air quality in Launceston was associated with reductions in mortality.”
The study was supported by the Australian Research Council, the Tasmanian Government Department of Health and Human Services, and the Environment Protection Authority Tasmania.
The researchers reported having no conflicts of interest to disclose.
Primary source: BMJ
Johnston FH, et al “Evaluation of interventions to reduce air pollution from biomass smoke on mortality in Launceston, Australia: retrospective analysis of daily mortality, 1994-2007” BMJ 2013; 345: e8446.
— Last Edited by Health_Freedoms at 2013-01-09 12:29:54 —