Wood smoke exposure, COPD and chronic bronchitis

Outside of the United States a number of research studies have looked at the connection between wood smoke, COPD and chronic bronchitis. While cigarette smoke exposure remains the number one cause of developing COPD worldwide, wood smoke exposure has been identified as a major contributing factor in many countries that utilize wood as a room heating and cooking heat source.


A new study published this month online ahead of print in the American Journal of Respiratory and Critical Care Medicine examines the connection between wood smoke and COPD/chronic bronchitis diagnosis in the United States. In the study, the research team found a significant correlation between wood smoke exposure and COPD/chronic bronchitis diagnosis among current smokers (and further noted higher odds among people of Hispanic origin and men of all origin). (Sood A, et al. Wood Smoke Exposure and Gene Promoter Methylation are Associated with Increased Risk for COPD in Smokers.Am J Respir Crit Care Med. 2010 Jul 1. [Epub ahead of print])

As the study authors explained, “In developed countries, people are exposed to wood smoke in a variety of ways, including smoke from residential heating, cooking stoves, campfires, forest fires, and prescribed fires. Wood burning is an important contributor to particle and gaseous material in ambient air, and in some locations accounts for up to 80% of the airborne particle concentrations during the winter...Wood burning not only increases indoor but also outdoor ‘neighborhood’ pollution; thereby exposing many non-users to wood smoke components… Wood smoke is a complex mixture of numerous volatile and particulate substances constituted by different organic and inorganic compounds known to be toxic or irritating to the respiratory system. Its composition varies with the wood type and the conditions of combustion. More than 200 chemical and compound groups have been identified, most of which are in the inhalable size range…Exposure to wood smoke in developed countries tends to be at sustained low-levels unlike exposure to cigarette smoke that is short-term but intense with a single cigarette…

Our study contrasts with most studies conducted outside the United States that have focused on non-smokers. Our population of relatively older smokers may be particularly susceptible to the adverse respiratory effects of wood smoke exposure, compared to the general population. This conclusion is supported by the observed additive effect between current cigarette smoke and wood smoke exposures on COPD phenotypes. Furthermore, these epidemiological findings are substantiated by our laboratory findings in which pulmonary inflammation and pathological changes were enhanced in mice concurrently exposed to wood smoke and cigarette smoke compared to cigarette smoke alone”.

In the study, researchers examined the medical records of the Lovelace Smoker Cohort. A Cohort is a group of people who have agreed to participate in an ongoing study, typically conducted over a generation. In such studies, subjects submit to periodic medical tests and examinations over time and also answer periodic surveys regarding a variety of health information. The Lovelace Smoker Cohort follows approximately 2,000 New Mexico residents who identified themselves as ever-smokers (study participants enrolled between 2001 and 2007).

The research team sampled approximately 1,800 relevant subjects from the cohort and reviewed surveys completed this sampling to identify those who self-reported exposure to wood smoke (approximately 500 people). Then the researchers examined spirometry results and sputum samples taken periodically for both the group exposed to wood smoke/cigarette smoke and those who were only exposed to cigarette smoke.

They discovered that those who were exposed to wood smoke and reported themselves as current cigarette smokers had a 116% higher odds ratio of being diagnosed with COPD than study subjects who were current smokers but were not exposed to wood smoke. Additionally, those exposed to wood/cigarette smoke had a 46% higher odds ratio of being diagnosed with chronic bronchitis.

Further, the study results revealed that the odds ratio of developing COPD among former smokers exposed to wood smoke was 36% higher than current cigarette smokers not exposed to wood smoke. This result implies that wood smoke is potentially more harmful than cigarette smoke in the odds of developing COPD. However, in contrast of this result, former smokers exposed to wood smoke had a 46% lower odds ratio of developing chronic bronchitis as compared to current smokers exposed to cigarette smoke only. So, there does not appear to be a correlation between wood smoke exposure and chronic bronchitis among former smokers.

Overall, the study seems to indicate that current smokers who regularly utilize wood as a cooking, heating, or brush removal fire source dramatically increase their odds of developing COPD and/or chronic bronchitis. If you are both a current smoker and are exposed to wood smoke frequently, these results suggest you can significantly reduce your odds of developing COPD and chronic bronchitis by halting your exposure to wood smoke. That is not to say that doing so will prevent you from being diagnosed with COPD and/or chronic bronchitis, especially if you are a current smoker. But any positive step you can take to avoid regular exposure to pollutants/irritants (such as wood smoke) that contribute to persistent airway inflammation and sputum production is surely a step in the right direction.