COPD and Asthma Overlap: Individual vs Environmental Risk Factors in Women

Smog over the city
Smog over the city
Socioeconomic and lifestyle risk factors had a more significant role in the development of COPD and asthma overlap syndrome in women than air pollution.

Individual risk factors have a more significant role than environmental factors in the development of asthma and chronic obstructive pulmonary disease (COPD) overlap syndrome in women, according to a study published in the Annals of the American Thoracic Society.

Recent studies have compared clinical profiles of asthma, COPD, and asthma and COPD overlap syndrome; however, they have shown a lack of information regarding modifiable risk factors (apart from tobacco use) for disease progression. This study sought to measure the incidence of COPD in women with asthma and characterize risk factors associated with development of asthma and COPD overlap syndrome.

The study recruited 4051 women with asthma who participated in the Canadian National Breast Cancer Screening Study from 1980 to 1985 and who were followed via Ontario health administrative databases from 1992 to 2015. At baseline, potential risk factors for the development of asthma and COPD overlap syndrome were reported via questionnaire. Data were collected on the patient’s age, history of tobacco use, body mass index, education, income, marital status, employment status, rurality, and medical history (including congestive heart failure, hypertension, diabetes, cancer, acute myocardial infarction, angina, ischemic heart disease, and stroke). Satellite data were used to estimate air pollution risk, specifically measuring the concentration of fine particulate matter by postal codes.

Of the 4051 participants, 1701 developed COPD. The primary study outcome measured the time between first documentation of asthma and the date of COPD incidence; death prior to COPD onset was considered a competing risk event. Risk factors were compared between participants with asthma only and those who developed asthma and COPD overlap syndrome. A multivariable competing risk regression model was used to assess the associations between risk factors and progression of COPD. Sociodemographic and lifestyle risk factors with significant links to the incidence of asthma and COPD overlap syndrome included older age, less education, unemployment, obesity, rural residency, and a history of tobacco use. Air pollution as a risk factor was not statistically significant.

Limitations of the study included a lack of generalizability due to a study population consisting of women recruited from a larger randomized controlled trial. Due to limited data, the investigators were unable to ascertain asthma incidence dates before 1992 and could not measure air pollution exposure before 2003.

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The identification of important modifiable risk factors associated with the incidence of asthma and COPD overlap syndrome included education, unemployment, body mass index, rurality, and tobacco use. Exposure to fine particulate matter was not significant, indicating that individual factors had a bigger role than environmental factors in the development of COPD. The authors suggested that prevention strategies targeting individual risk factors could potentially reduce the incidence of asthma and COPD overlap in this population.


To T, Zhu J, Gray N, et al. Asthma and COPD overlap in women: incidence and risk factors [published online July 17, 2018]. Ann Am Thorac Soc. doi:10.1513/AnnalsATS.201802-078OC