Aetiology

The most important cause of COPD is smoking.

• around half of all cigarette smokers will have some airflow obstruction present while 10 -20% will develop clinically significant COPD.
• pipe and cigar smoking is also associated with a significant increase in morbidity and mortality (but the risk is less than for cigarette smokers)
• an increased risk of COPD in passive smokers or environmental tobacco smoke (ETS) has also been observed in several case-controlled studies (1)

Other causes include:

• indoor air pollution
  • caused by burning of wood, animal dung, crop residues, coal burnt in open fires or in poorly functioning stoves
  • from biomass cooking and heating in poorly vented dwelling
• occupational exposure to toxins, e.g. coal dust and cadmium
  • is an under-appreciated risk factor of COPD
  • the risk was estimated to be 20% in diagnosed COPD cases but in lifelong non-smokers this number is increased to 30% (2)
  • the risk of developing COPD is significantly increased in cigarette smokers who are exposed to occupational toxins (3)
• outdoor air pollution, e.g. exhaust fumes,
  • its role in COPD is unclear, appears to have a relatively small effect in causing COPD
• genetic factors
  • mutations in the SERPINA1 gene that leads to hereditary deficiency of alpha-1-antitrypsin (AATD) (2)
  • is the best-documented genetic risk factor and is seen in only 1-2% of patients with COPD
  • premature and accelerated development of COPD in both smokers and non-smokers is linked with severe deficiency of α1- antitrypsin.
  • patients who are less than 40 years with severe COPD should be investigated for alpha-1-antitrypsin status since in more than half of patients there is a deficiency (2)
• infections
  • childhood infections, e.g. measles or whooping cough, are associated with reduced lung function and increased respiratory symptoms in adulthood
  • acute infections cause exacerbation of COPD
• lung growth and development
  • factors which occur during gestation, birth, and exposures during childhood and adolescence increase the risk of developing COPD
• socioeconomic status
  • risk of developing COPD is seen in people with lower socioeconomic status
• asthma and airway hyper-reactivity
  • increased risk of developing chronic airflow limitations and COPD is seen in asthma patients
• chronic bronchitis
  • various studies have reported an association between mucous hypersecretion and increased FEV1 decline
  • an increased risk of developing COPD is observed in younger adults with chronic bronchitis who smoke (1,2)

Reference:

1. Li X, Cao X, Guo M, et al. Trends and risk factors of mortality and disability adjusted life years for chronic respiratory diseases from 1990 to 2017: systematic analysis for the Global Burden of Disease Study 2017. BMJ. 2020 Feb 19;368:m234.
2. Global Initiative for Chronic Obstructive Lung Disease (GOLD). Global strategy for the diagnosis, management, and prevention of chronic obstructive pulmonary disease: 2025 report. 2025 [internet publication].