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What is chronic obstructive pulmonary disease?

Chronic obstructive pulmonary disease (COPD) is a lung disease that is most often caused by smoking. The damage caused by smoking and the resulting chronic inflammation in the lungs and other airways makes it very hard for a person with COPD to breathe.1 COPD is an often progressive disease, meaning that the symptoms get worse over time. COPD is more prevalent in smokers and ex-smokers, adults over 40 years of age, and men.2

The Global Initiative for Chronic Obstructive Lung Disease (GOLD) grades the severity of a patient’s COPD by measuring how limited their airflow is with a breathing test known as a spirometry test. A spirometry test measures the amount and speed of air you exhale in one second (FEV1).

In the U.S. in 2014, 6% of Americans had COPD, with over 16 million diagnosed with the disease. That same year, COPD was the third leading cause of death in the U.S., with 39.1 deaths per 100,000 people.3

What are the symptoms?

COPD can be characterized by a wide variety of symptoms. The main symptoms of COPD are (in order of frequency)1:

  • Wheezing and chest tightness
  • Coughing
  • Sputum production
  • Fatigue
  • Chronic and progressive shortness of breath
  • Significant airflow limitation

COPD symptoms usually get worse over time, especially in COPD patients who continue to smoke. COPD patients often experience flare-ups called exacerbations in which their symptoms suddenly become more severe, often during an upper respiratory infection. These exacerbations can last several days and may require more aggressive treatment, including steroids and/or antibiotics.4

According to the number and severity of a patient’s symptoms, COPD may be classified from “A” to “D”, with “D” as the most severe. For a complete COPD diagnosis, a combined assessment of the patient’s spirometric classification, symptoms, exacerbation risk (the risk of experiencing an acute episode of severe respiratory distress), and other diseases must be conducted.2,5

 What are the causes?

Foreign inhaled particles – such as cigarette smoke, gas, air pollutants, and chemicals – cause chronic inflammation in the lungs. This inflammatory response may destroy tissue over time and disrupt normal repair and defense mechanisms, resulting in structural changes in the lungs. These changes lead to even more air trapping (when you struggle to exhale all the air in your lungs) and limited airflow. Later stage complications include low oxygen levels, risk of pneumonia, pulmonary hypertension, and heart failure.1,5

The main and most studied risk factor for COPD is smoking. That said, the disease can also occur in non-smokers, although the cause and mechanism for chronic airflow inflammation in non-smoking patients is not fully understood. Other risk factors include2:

  • Aging
  • Asthma and airway hyperreactivity
  • Chronic bronchitis
  • Exposure to particles, chemicals, and smoke
  • Genetics
  • History of severe childhood respiratory infection
  • Limited lung growth as a child
  • Lower socioeconomic status
  • Male sex

How does this topic relate to my microbiome?

Several studies have shown a rich lung microbiome in COPD patients that clearly differs from a healthy lung.6 Lung microbiota composition in COPD varies widely depending on the portion of the lung being analyzed, and/or the disease stage.7

Common bacteria phyla associated with COPD are Proteobacteria, Bacteroidetes, Actinobacteria, and Firmicutes.6,7 Compared to healthy individuals, Proteobacteria and Actinobacteria are more abundant in COPD affected lungs, and Firmicutes and Bacteroides are less abundant.8 Lung microbiota studies are recent, so there is no clear evidence yet on how bacteria affect the onset and development of the disease.

Which diseases/topics are related to COPD?

Some respiratory conditions share symptoms with COPD. A diagnosis of one of these may be considered:

  • Asthma
  • Respiratory tract infections, including bronchitis or pneumonia
  • Other obstructive lung disease

Other related comorbidities of COPD are (in order of relevance)9,10:

  • Cardiovascular disease
  • Diabetes
  • Lung cancer
  • Allergic disease
  • Anxiety
  • Anemia
  • Cognitive dysfunction
  • Depression
  • Gastroesophageal reflux
  • HIV infection
  • Insomnia, poor sleep quality, and daytime sleepiness
  • Metabolic syndrome
  • Obesity
  • Osteoporosis
  • Parkinson’s disease

How can I take action?

External risk factors can be avoided by2,11:

  • Quitting smoking
  • Avoiding exposure to pollutants and smoke

If you notice any COPD symptoms, ask your healthcare provider to properly evaluate your condition. Treatment options for COPD include (in order of frequency)2,11:

  • Medications, such as bronchodilators and/or steroids
  • Pulmonary rehabilitation
  • Avoiding lung infections
  • Supplemental oxygen


1. Vestbo, J., Hurd, S. S., Agustí, A. G., Jones, P. W., Vogelmeier, C., Anzueto, A., … Rodriguez-Roisin, R. (2013). Global strategy for the diagnosis, management, and prevention of chronic obstructive pulmonary disease GOLD executive summary. American Journal of Respiratory and Critical Care Medicine, 187(4), 347–365.

2. GOLD (2018). Global Initiative for Chronic Obstructive. Global Obstructive Lung Disease.

3. Centers for Disease Control and Prevention (2018). Chronic Obstructive Pulmonary Disease (COPD).

4. Mayo Clinic (2017). COPD.

5. Vijayan, V. K. (2013). Chronic obstructive pulmonary disease. The Indian Journal of Medical Research, 137(2), 251–269.

6. Faner, R., Sibila, O., Agustí, A., Bernasconi, E., Chalmers, J. D., Huffnagle, G. B., … Monsó, E. (2017). The microbiome in respiratory medicine: Current challenges and future perspectives. European Respiratory Journal, 49(4), 1–12.

7. Huang, Y. J., Erb-Downward, J. R., Dickson, R. P., Curtis, J. L., Huffnagle, G. B., & Han, M. L. K. (2017). Understanding the role of the microbiome in chronic obstructive pulmonary disease: principles, challenges, and future directions. Translational Research, 179, 71–83.

8. Sze, M. A., Dimitriu, P. A., Suzuki, M., McDonough, J. E., Campbell, J. D., Brothers, J. F., … Hogg, J. C. (2015). Host response to the lung microbiome in chronic obstructive pulmonary disease. American Journal of Respiratory and Critical Care Medicine, 192(4), 438–445.

9. Divo, M., Cote, C., De Torres, J. P., Casanova, C., Marin, J. M., Pinto-Plata, V., … Celli, B. (2012). Comorbidities and risk of mortality in patients with chronic obstructive pulmonary disease. American Journal of Respiratory and Critical Care Medicine, 186(2), 155–161.

10. Putcha, N., Drummond, M., Wise, R., & Hansel, N. (2015). Comorbidities and Chronic Obstructive Pulmonary Disease: Prevalence, Influence on Outcomes, and Management. Seminars in Respiratory and Critical Care Medicine, 36(04), 575–591.

11. Qaseem, A. (2011). Diagnosis and Management of Stable Chronic Obstructive Pulmonary Disease: A Clinical Practice Guideline Update from the American College of Physicians, American College of Chest Physicians, American Thoracic Society, and European Respiratory Society. Annals of Internal Medicine, 155(3), 179.