aetiology

Last edited 04/2018 and last reviewed 02/2021

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 cigarettes smokers)
• an increased risk of COPD in passive smokers or environmental tobacco smoke (ETS) have 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
  • such as severe hereditary deficiency of alpha-1-antitrypsin (AATD)
• 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 the 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 α1- antitrypsin status since in more than half of patients there is a deficiency (2)

• infections
  • childhood infections, e.g. measles or whooping cough is 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) Currie, G.P. (Ed.) (2011) ABC of COPD. Oxford: Blackwell Publishing  
• (2) Global Initiative for Chronic Obstructive Lung Disease (GOLD) 2018. Global strategy for the diagnosis, management, and prevention of chronic obstructive pulmonary disease.