Study Finds Variation in COPD Characteristics by Risk Factors

Patients with chronic obstructive pulmonary disease (COPD) may experience a difference in symptom severity depending on which risk factors they are exposed to across their lifetime.

A recent study of Chinese patients with chronic obstructive pulmonary disease (COPD) found variation in disease characteristics among patients exposed to different risk factors, including tobacco exposure, biomass smoke, and occupational exposure, either individually or in combination.

“The information provided here can act as a guide to warn doctors of the effects of these risk factors and to encourage them to take effective action to improve the targeted prevention of COPD,” wrote the authors of the study published in the International Journal of Chronic Obstructive Pulmonary Disease.

COPD is the third-leading cause of death worldwide and is estimated to affect more than 174.5 million people globally. In China, an estimated 13.7% of the population 40 years and older have COPD.

Tobacco smoking is commonly identified as a risk factor for COPD, but previous research has found that COPD has other risk factors, including exposure to biomass smoke, which refers to the energy produced from organic products used as fuel for heating and cooking in poorly ventilated residences, and occupational exposure to dust, gases, coal, and other toxic chemicals.

Oftentimes, risk factors can overlap with each other, making it “difficult to disentangle the effects of overlapping exposures on the development of COPD,” the investigators wrote.

The cross-sectional analysis in their study included data from 5183 patients from the central-south region of China who were 40 years or older and had COPD.

Researchers defined tobacco exposure as having smoked at least 10 pack-years in their lifetime. Exposure to biomass smoke was defined as people who use biomass fuels, such as wood, grass, charcoal, and crop residues, for cooking or heating at least 2 hours per day for at least 1 year. Occupational exposure was defined as having exposure to dust, gases/fumes, insecticides, chemical substances, paints, and metals for at least 8 hours per day for more than 1 year at work.

Patients were divided into 5 groups based on their exposure history: patients exposed to tobacco alone; patients exposed to tobacco in combination with other risk factors, including biomass smoke and occupational exposure; patients exposed to biomass smoke alone; patients exposed to occupational exposure alone; and patients exposed to risk factors excluding tobacco, biomass smoke, and occupational exposure.

Among the 3688 patients identified as smokers, 2168 (58.7%) were exposed to tobacco only and 1520 (41.2%) were exposed to tobacco and other risk factors including biomass smoke and toxic chemicals resulting from work conditions.

Patients who were exposed to tobacco and other risk factors had a greater chance (41.5%) of experiencing acute COPD exacerbations than those solely exposed to tobacco (29.3%; P < .001).

Patients exposed to a combination of tobacco and other risk factors were also found to have higher mean (SD) COPD Assessment Test (CAT) scores (16.0 [ 6.7] vs 15.3 [6.3]; P = .003) and more severe dyspnea, which was categorized as having a score on the modified Medical Research Council (mMRC) scale greater than 2. Investigators reported that these patients specifically had more severe chest tightness and significantly affected sleep.

“This finding suggests that combined exposure to tobacco plus other risk factors has a noxious additive effect in COPD patients and could result in more serious COPD symptoms,” noted the authors.

Further, patients in the tobacco alone group were less likely than patients in the biomass alone group and the occupational exposure alone group to develop more severe dyspnea (61.6% vs 74.2% and 70.8%, respectively; P < .05) and to have lower exacerbation ratios (29.3% vs 44.9% and 47.8%, respectively; P < .05).

Of the 1495 nonsmokers, 423 (28.2%) patients had only been exposed to biomass smoke, 527 (35%) had only occupational exposures, and 545 (36.5%) patients were exposed to risk factors other than the 3 included in the study.

The group exposed to solely biomass smoke consisted of mostly women and had the highest mean (SD) CAT scores (17.5 [6.3]) compared with the tobacco alone group (15.3 [6.3]), the occupational exposure alone group (15.2 [6.3]), and the group exposed to other risk factors (16.3 [6.6]) (P < .05 for all). This group also had more frequent exacerbations (P = .010) and higher mMRC scores (P = .030) than the tobacco alone group.

Researchers said this group was made up mostly of women due to Chinese traditions establishing that women do most of the cooking; thus, women are often the ones using biomass fuels. Additionally, poor ventilation in kitchens can exist in rural or remote areas that may not have easy access to hospitals, leading to patients forgoing medical care until they have obvious symptoms of COPD.

The group exposed to noxious chemicals due to their occupation included the youngest patients. Investigators noted that China’s laws that establish protective measures for workers to control occupational diseases allows workers to have free medical examinations and increases the likelihood of an early COPD diagnosis.


Duan JX, Cheng W, Zeng YQ, et al. Characteristics of patients with chronic obstructive pulmonary disease exposed to different environmental risk factors: a large cross-sectional study. Int J Chron Obstruct Pulmon Dis. 2020;15:2857-2867. doi:10.2147/COPD.S267114