Risk factors associated with COPD

COPD shares a number of risk factors with other chronic diseases, such as:

Non-modifiable risk factors

  • age (COPD is more common as people age)
  • genetic predisposition

Modifiable risk factors

  • smoking or exposure to environmental tobacco smoke (including in childhood)
  • exposure to fumes and smoke from carbon-based cooking and heating fuels such as charcoal and gas
  • occupational hazards (for example, exposure to pollutants and chemicals)
  • poor nutrition
  • pneumonia or childhood respiratory infection.

In people with COPD, risk factors for poor health outcomes such as worsening symptoms, exacerbations (flare-ups) and increased risk of death include [1]:

  • smoking and exposure to environmental tobacco smoke
  • being underweight
  • physical inactivity
  • presence of comorbidities
  • cold weather.

For COPD, as for many other chronic conditions, there are two types of risk factors: those that increase the chance of developing COPD in the first place, and those that increase the chance that a person who already has COPD will develop additional health problems. Risk factors also vary according to the person's age.

Finding a factor that is associated with an increased risk of developing COPD, or an increased risk of poor health outcomes in COPD, does not necessarily mean that the risk factor caused these problems, or that they can be prevented. However, there is overwhelming evidence that smoking and exposure to biomass fuels are major causes of COPD.

Common risk factors

Based on the 2014–15 National Health Survey (NHS), people with self-reported COPD were more likely to be current smokers, physically inactive and/or obese, compared to those without COPD (see Figure 1). Risk factor definitions are included in Box 1 (under data notes). These risk factors are also common among other chronic conditions [2].

Figure 1: Prevalence of risk factors in people aged 18 and over with and without COPD, 2014–15

figure1-risk-factors-copd-comorbidities

Notes

  1. The thin vertical lines attached at the end of each bar are 95% confidence intervals. We can be 95% confident that the true value is within this confidence interval.
  2. Physically inactive includes inactive and insufficiently active.

Source: Australian Health Survey: National Health Survey, 2014–15 (First results and customised report ABS 2016) (Data table).

Selected risk factors

Smoking status

People with COPD were more likely to report having been a smoker, with:

  • 24.1% being a current daily smoker (compared with 14.2% without COPD)
  • 45.3% being an ex-smoker (compared with 30.9% without COPD) (Figure 2).

Tobacco smoking is one of the leading behavioural risk factors for death from all causes and contributes significantly to deaths from a range of chronic conditions (including CVD, COPD, and lung cancer). Tobacco smoking is the predominant cause of COPD and is associated with a majority of COPD cases [3]. Lifelong smokers have a 50% probability of developing COPD during their lifetime [4].

Once COPD has developed, continued smoking increases the risk of exacerbations (flare-ups) and the risk of death, not only from COPD but also from other causes such as cancer and cardiovascular disease. While the damage from past smoking is not fully reversible, the rate of progression of COPD can be reduced through smoking cessation [4]. Quitting smoking also reduces the risk of exacerbations and mortality in patients with COPD [5, 6].

GPs play an important role in encouraging and supporting people to quit smoking, especially when they have health problems caused or exacerbated by smoking, which are more common with age [7]. In Australia, smoking rates have been falling amongst males since the 1950s (1970s in women) [8], and recent studies have shown that smoke free laws, tobacco price increases and mass media campaigns have all contributed to a continuing decline in smoking rates, including among young people [9].

Figure 2: Smoker status of people aged 18 and over with and without COPD, 2014–15

figure2-risk-factors-copd-comorbidities

Notes

  1. The thin vertical lines attached at the end of each bar are 95% confidence intervals. We can be 95% confident that the true value is within this confidence interval.

  2. None of the people aged 18 and over with COPD were occasional smoker.

Source: ABS National Health Survey, 2014–15 (First results and customised report ABS 2016) (Data table).

Physical activity

People with self-reported COPD were less likely than people without COPD to report engaging in the recommended levels of moderate or vigorous physical activity. For adults with COPD, 70.8% reported being physically inactive (either inactive or insufficiently active) compared with 54.0% of those without COPD (Figure 3).

One of the main features of COPD is shortness of breath on exertion. As the condition progresses, shortness of breath can worsen and even minor physical activities such as dressing or showering can become very difficult. People with COPD therefore are often unable to exercise as much as those without COPD, or they may limit their physical activity to avoid becoming short of breath. However, low physical activity in turn leads to lack of cardiovascular fitness, increased risk of cardiovascular disease, and obesity, each of which may further worsen shortness of breath.

Exercise-based pulmonary rehabilitation is an important part of management of COPD, as it improves quality of life and exercise capacity and reduces hospitalisations. It is recommended for all patients with COPD, especially those with exercise limitations. For more information regarding pulmonary rehabilitation, refer to Monitoring pulmonary rehabilitation and long-term oxygen therapy for people with chronic obstructive pulmonary disease (COPD).

Figure 3: Physical activity in people aged 18 and over with and without COPD, 2014–15

figure3-risk-factors-copd-comorbidities

Note: The thin vertical lines attached at the end of each bar are 95% confidence intervals. We can be 95% confident that the true value is within this confidence interval.

Source: ABS National Health Survey, 2014–15 (First results and customised report ABS 2016) (Data table).

Body weight

People with self-reported COPD were 1.5 times as likely to report being obese than people without COPD (41.6% with COPD compared with 27.5% without COPD) (Figure 4).

Several studies have shown strong associations between overweight and obesity, as measured by body mass index (BMI), and increased prevalence of COPD [10]. This is not surprising, as the prevalence of both COPD and obesity increase with increasing age. There is little evidence that high BMI increases the risk of developing COPD. However, obesity is a risk factor for dyspnoea (or shortness of breath), which may contribute to symptoms of COPD and may also reduce lung function.

For patients who already have COPD, many studies have shown that mild obesity appears to be protective from risk of death, unlike many other chronic diseases in which increased bodyweight is associated with worse outcomes. Being underweight or average weight is associated with increased risk of dying for people with COPD [11]. The relationship between low BMI and increased mortality is particularly seen in patients with more severe COPD, of whom around 14% experience substantial weight loss and reduced fat-free mass [11]. This may be due to systemic inflammation associated with COPD, leading to muscle wasting [10]. Reduced micronutrient intake may also contribute to increased risk [11].

Figure 4: Proportion of people aged 18 and over with and without COPD by body mass index (BMI), 2014–15

figure4-risk-factors-copd-comorbidities

Notes

  1. The thin vertical lines attached at the end of each bar are 95% confidence intervals. We can be 95% confident that the true value is within this confidence interval.
  2. Based on Body Mass Index (BMI) for persons whose height and weight was measured.

Source: ABS National Health Survey, 2014–15 (First results and customised report ABS 2016) (Data table).

Age differences in risk factors in people with COPD

People with COPD aged 45–64 (31.8%) were more likely to report current daily smoking than those aged 65 and over (14.8%) (Figure 5). Between the two age groups, the difference in the prevalence of physical inactivity or overweight and obesity were not statistically significantly different.

Figure 5: Prevalence of risk factors in people with COPD, by age, 2014–15

figure5-risk-factors-copd-comorbidities

Note: The thin horizontal lines attached at the end of each bar are 95% confidence intervals. We can be 95% confident that the true value is within this confidence interval.

Source: ABS National Health Survey, 2014–15 (First results and customised report ABS 2016) (Data table).

Data notes

This analysis is based on data only for people aged 45 and over. This age group was selected because the development of COPD occurs over many years and therefore mainly affects older people, and positive responses to the questions about 'bronchitis and/or emphysema' in the National Health Survey (NHS) from younger people are more likely to include more cases of acute bronchitis or asthma than COPD itself.

The risk factor data presented here were obtained at one point in time, based on self-reported data from the NHS. When interpreting self-reported data, it is important to recognise that it relies on respondents providing accurate information.

It is not possible to attribute cause and effect to self-reported risk factors and COPD. Risk factors present at the time of the survey may or may not have contributed to the presence of COPD. Similarly, the presence of COPD may not be directly related to the number of risk factors a person has.

The risk factor definitions used in the ABS 2014–15 National Health Survey are described below in Box 1.

Box 1: Definitions for risk factors in the National Health Survey

Smoking

Smoking status is defined by the extent of regular smoking of tobacco at the time of interview. This includes manufactured (packet) cigarettes, roll-your-own cigarettes, cigars and pipes, at time of interview. It excludes chewing tobacco and smoking of non-tobacco products. The categories reported in the NHS are:

Current daily smoker—Regularly smoking one or more cigarettes, cigars or pipes per day

Current smoker (occasional)—Smoking cigarettes, cigars or pipes less frequently than daily (weekly or less than weekly)

Ex-smoker—Not currently smoking, but smoked daily, or at least 100 cigarettes, or pipes, cigars, etc. at least 20 times in lifetime

Never smoked—Never regularly smoked daily, and smoking less than 100 cigarettes in the lifetime and/or smoking pipes, cigars, etc. less than 20 times in the lifetime.

Physical activity

According to the Australian Physical Activity and Sedentary Behaviour Guidelines, physical activity is defined as any bodily movement that requires energy expenditure (Department of Health 2014). This includes walking (for transport, fitness, recreation, or sport). For the purpose of calculating activity time, vigorous activity time is multiplied by a factor of two. The categories include:

Inactive*—Not doing any physical activity (including walking for transport and fitness, and moderate and vigorous activity) in the week before interview

Insufficiently active*—Not completely inactive but failing to meet the requirement of at least 150 minutes of physical activity (including walking for transport and fitness, and moderate and vigorous activity) over five separate sessions in a given week.

Sufficiently active for health—Participation in at least 150 minutes of physical activity (including walking for transport and fitness, and moderate and vigorous activity) over five separate sessions in a given week.

*For the present analyses, physical inactivity means not achieving the recommended amounts of physical activity of 150 minutes per week over at least five days. This includes the above categories of inactive and insufficiently active.

Body weight

Based on body mass. Categories of body mass were derived from the body mass index (BMI)—calculated by dividing a person's weight in kilograms by the square of their height in metres (kg/m2). The standard recommended by the World Health Organization to measure BMI for adults aged 18 and over is:

Underweight—Less than 18.50

Normal range—18.50 – 24.99

Overweight—25.00 – 29.99

Obese—30.00 or more

Source: ABS 2013. Australian Health Survey: Users’ Guide, 2011–13 [12].

References

  1. Lung Foundation Australia. 2015. COPD-X Guidelines - Version 2.44. Viewed 16 February 2016.
  2. Australian Bureau of Statistics (ABS) 2015. National Health Survey: First Results, 2014–15. ABS Cat. no. 4364.0.55.001. Canberra: ABS.
  3. Yawn B, & Kaplan A. 2008. Co-morbidities in people with COPD: a result of multiple diseases, or multiple manifestations of smoking and reactive inflammation? Primary Care Respiratory Journal 17(4): 199–205.
  4. Laniado-Laborin R. 2009. Smoking and chronic obstructive pulmonary disease (COPD). Parallel epidemics of the 21st century. International Journal of Environmental Research and Public Health 6: 209–224.
  5. Anthonisen NR, Skeans MA, Wise RA, Manfreda J, Kanner RE, Connett JE, et al. 2005. The effects of a smoking cessation intervention on 14.5-year mortality: a randomized clinical trial. Annals of Internal Medicine. 142: 233–239.
  6. Au DH, Bryson CL, Chien JW, Sun H, Udris EM, Evans LE et al. 2009. The Effects of Smoking Cessation on the Risk of Chronic Obstructive Pulmonary Disease Exacerbations. Journal of General Internal Medicine. 24: 457–463.
  7. Royal Australian College of General Practice (RACGP) 2014. Supporting smoking cessation: a guide for health professionals. Melbourne: The Royal Australian College of General Practitioners.
  8. Greenhalgh EM, Bayly M, & Winstanley MH. Chapter 1. Trends in the prevalence of smoking. In M.M. Scollo, & M.H. 2015. Winstanley [Eds]. Tobacco in Australia: Facts and Issues. Viewed 16 February 2016.
  9. Wakefield MA, Coomber K, Durkin SJ, Scollo M, Bayly M, Spittal MJ, et al. 2014. Time series analysis of the impact of tobacco control policies on smoking prevalence among Australian adults, 2001-2011. Bulletin of the World Health Organization 92:413–22.
  10. van der Molen T. 2010. Co-morbidities of COPD in primary care: frequency, relation to COPD, and treatment consequences. Primary Care Respiratory Journal 19(4): 326–334.
  11. Hanson C, Rutten EP, Wouters EFM, Rennard S. 2014. Influence of diet and obesity on COPD development and outcomes. International Journal of Chronic Obstructive Pulmonary Disorders. 9: 723–33.
  12. Australian Bureau of Statistics (ABS) 2013. Australian Health Survey: Users’ Guide, 2011–13. Viewed 16 August 2015.