Combined wood and tobacco smoke exposure increases risk and symptoms of COPD

People who are consistently exposed to both wood smoke and tobacco smoke are at a greater risk for developing chronic obstructive pulmonary disease (COPD) and for experiencing more frequent and severe symptoms of the disease, as well as more severe airflow obstruction, than those who are exposed to only one type of smoke, according to the results of a new population-based study conducted by researchers in Colombia.

"Although previous studies have shown a definite link between wood smoke exposure and the development of COPD, those studies were case-controls and case series of patients with similar disease or health profiles," said study lead author Carlos Torres-Duque, M.D., director of research at the Fundacion Neumologica Colombiana in Bogota. "This new data derives from a population-based study that looked at wood smoke exposure and the overall prevalence of COPD, as well as the characteristics of the disease and those who suffer from it."

About 40 percent of the world's population uses solid fuels – especially wood – for cooking or heating, he noted.

For this study, Dr. Torres-Duque and his colleagues used data from the PREPOCOL (Prevalencia de la Enfermedad Pulmonar Obstructiva Crónica en Colombia) study which evaluated the prevalence of COPD among the adult residents of five Colombian cities. The study included 5,539 subjects, 8.9 percent of whom were diagnosed with COPD. The study participants were divided into four groups: those who were exposed to wood smoke and who had never smoked tobacco (30.9 percent); those who were exposed to tobacco smoke but had no exposure to wood smoke (18.7 percent); those who had been exposed to both types of smoke (29.8 percent); and those who had exposure to neither type of smoke (20.6 percent).

Patients' lung function was measured using spirometry, a technique used to measure the amount of air a person is able to inhale and exhale, and all patients completed a standardized respiratory questionnaire to identify exposure to smoke.

In their initial review of data, the researchers learned that 53 percent of those diagnosed with COPD had both wood and tobacco smoke exposure; moreover, the prevalence of COPD increased as exposure to wood smoke increased.

After adjusting for specific factors including age, active and passive tobacco smoking, education level, history of TB and altitude, the researchers found that wood smoke exposure of 10 or more years posed a significant risk factor for developing COPD in both men and women and those with both wood and tobacco exposure had poorer lung function scores and more phlegm and coughed more frequently than those who had exposure to only one type of smoke.Among the COPD population, those who were exposed only to wood smoke tended to be women, to have higher BMIs and to be shorter than those exposed to tobacco smoke or to a combination of wood and tobacco smoke.

"In the population we studied, exposure to wood smoke was identified as an independent risk factor for developing COPD, both in women and men," Dr. Torres-Duque said. "In addition, the prevalence of COPD was significantly higher in those who were exposed to both wood and tobacco smoke and those with both exposures had more symptoms and more severe disease than those who were exposed to only one type of smoke."

This result suggests that the combination of wood and tobacco smoke produces an additive effect that causes an increase in COPD prevalence and in the frequency of COPD symptoms, he added.

"It is also possible that the responses of the lungs and airways could vary, based on the pollutants to which they're exposed," Dr. Torres-Duque noted.

Future studies might provide additional data regarding varying responses and help clinicians determine specific treatments based on exposures, he said.