Risk factors associated with asthma

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

Non-modifiable risk factors

  • genetic predisposition.

Modifiable risk factors

  • tobacco use (smoking or exposure to cigarette smoke)
  • exposure to environmental hazards (for example, exposure to air pollutants)
  • overweight/obesity
  • sedentary lifestyle.

Other risk factors

  • allergic rhinitis [1].

Risk factors may increase the chance of developing asthma in the first place (either in childhood or as an adult), or may increase the chance that a person with asthma will develop additional health problems. Risk factors also vary according to the person's age, and according to the type of asthma that they have. Finding a factor that is associated with asthma, or poor health outcomes in asthma, does not necessarily mean that the risk factor caused these problems, or that they can be prevented.

In people with asthma, risk factors associated with an increased risk of flare-ups include [2]:

  • having frequent symptoms (e.g. more than 2 days/week)
  • not taking preventer treatment regularly (medicines used every day in asthma control to minimise symptoms and reduce the likelihood of episodes or flare-ups. Inhaled corticosteroids are the most commonly used preventers [3])
  • frequent reliever inhaler use (medicines used for the rapid relief of asthma symptoms when they occur [3])
  • comorbidities (e.g. mental illness, obesity, chronic rhino sinusitis)
  • major socioeconomic problems
  • exposure to smoking, allergens, air pollution.

Common risk factors

Based on the 2017–18 National Health Survey (NHS), people with asthma were more likely to be current daily smokers, insufficiently physically active and/or obese, compared with those without asthma (see Figure 1). Risk factor definitions are included in Box 1 (in the data notes section). These risk factors are also common among other chronic conditions.

Figure 1: Prevalence of selected risk factors in people aged 18 and over with and without asthma, 2017–18

The bar chart shows risk factors in adults with and without asthma in 2017–18. People aged 18 years and over with asthma were more likely to be current daily smokers (17%25 compared with 13%25 among people without asthma), insufficiently physically active (59%25 compared with 54%25 among people without asthma) and obese (42%25 compared with 30%25 among people without asthma).
 

Note: Overweight and obese are based on Body Mass Index (BMI) for persons whose height and weight was measured and imputed. In 2017–18, 33.8% of respondents aged 18 years and over did not have a measured BMI. For these respondents, imputation was used to obtain BMI. For more information see Appendix 2: Physical measurements in the 2017–18 National Health Survey [4].

Source: AIHW analysis of ABS 2019 [5] (Data table).

Selected risk factors

Smoker status

Compared with people without asthma, people with asthma were more likely to be current daily smokers (17% compared with 13% for people without asthma), and less likely to have never smoked (50% compared with 55% for people without asthma) (see Figure 2).

Tobacco use or exposure to environmental tobacco smoke are risk factors associated with the development of asthma. The interaction between exposure to tobacco smoke and development of asthma symptoms varies with age. Parental smoking during pregnancy or infancy is linked to asthma symptoms in children [6], and smoking by a parent or child/adolescent is linked to asthma symptoms in adolescence [7].  

For people who already have asthma, smoking or exposure to environmental tobacco smoke can increase the risk of flare-ups and need for emergency care for asthma [8]. In people with asthma, smoking is also associated with a reduced effectiveness of inhaled corticosteroids [9, 10].    

Figure 2: Smoker status of people aged 18 and over with and without asthma, 2017–18

The bar chart the shows smoker status of adults with and without asthma in 2017–18. People aged 18 years and over with asthma were more likely to be current daily smokers (17%25 compared with 13%25 among people without asthma) and less likely to have never smoked (50%25 compared with 55%25 among people without asthma).

Source: AIHW analysis of ABS 2019 [5] (Data table).

Physical activity

Sufficient physical activity (for example, regular exercise) is an important factor associated with positive health outcomes. Insufficient physical activity is a risk factor for several chronic conditions. It is also associated with overweight and obesity, and poorer health outcomes more generally. See Box 1 for definitions of physical activity.

Evidence suggests that sedentary behaviour (as measured by television viewing) is associated with asthma symptoms in children [6]. The association between physical activity and asthma symptoms may be complicated by the fact that, in some people who already have asthma, physical activity may trigger asthma symptoms, particularly if their asthma is poorly controlled.

Physical activity is generally recommended to adults and children with asthma as a way to manage the disease and improve quality of life [3].

Based on the 2017–18 NHS, people with asthma were less likely than people without asthma to engage in sufficient physical activity (42% compared with 46% for people without asthma) (Figure 3).

Figure 3: Physical activity in people aged 18 and over with and without asthma, 2017–18

The bar chart shows physical activity of adults with and without asthma in 2017–18. People aged 18 years and over with asthma were more likely to be insufficiently physically active (59%25 compared with 54%25 among people without asthma).

Source: AIHW analysis of ABS 2019 [5] (Data table).

Body mass

People with asthma were 1.4 times as likely to be obese (by BMI — see data notes) as people without asthma (42% with asthma compared with 30% without asthma) (Figure 4).

Studies show there are associations between overweight and obesity, as measured by BMI, and asthma, especially in high income countries [1]. Additionally, people with asthma who are overweight or obese often experience complications in treatment. For people who are overweight or obese, weight loss has been shown to reduce treatment complications and improve symptoms [11, 12]. There is evidence of an association between being obese and developing asthma; however, the causative mechanisms between body mass and asthma are not currently well understood [13, 14].

Figure 4: Proportion of people aged 18 and over with and without asthma by BMI, 2017–18

The bar chart shows BMI of adults with and without asthma in 2017–18. People aged 18 and over with asthma were more likely to be obese (42%25 compared with 30%25 among people without asthma).

Note: Based on Body Mass Index (BMI) for persons whose height and weight was measured and imputed. In 2017–18, 33.8% of respondents aged 18 years and over did not have a measured BMI. For these respondents, imputation was used to obtain BMI. For more information see Appendix 2: Physical measurements in the 2017–18 National Health Survey [4].

Source: AIHW analysis of ABS 2019 [5] (Data table).

Age differences in risk factors in people with asthma

For people with asthma, the prevalence of risk factors varies by age.

The prevalence of smoking in people with asthma was higher in the earlier years of life. People aged 18–44 and 45–64 with asthma were more likely to be a current daily smoker (19% and 20%, respectively) compared with those aged 65 and over (7.6%) (Figure 5). Smoke free laws, tobacco price increases and greater exposure to mass media campaigns may contribute to lower smoking rates among older Australians [15]. 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 increasing age [16].

Among people with asthma, 50% of those aged 18–44 were insufficiently physically active, compared with 60% of those aged 45–64 and 76% of those aged 65 and over. Those aged 45–64 were less likely to be insufficiently physically active compared with those aged 65 and over.

Among those with asthma aged 18–44, 35% were obese, compared with 48% of those aged 45–64 and 49% of those aged 65 and over.

Figure 5: Prevalence of risk factors in people aged 18 and over with asthma, by age, 2017–18

The bar chart shows risk factors among adults with asthma in 2017–18, by age group. Adults aged 18–64 and 45 to 64 with asthma were more likely to be a current daily smoker (19%25 and 20%25, respectively) compared with people with asthma aged 65 and over (7.6%25). Adults aged 65 and over with asthma were more likely to be insufficiently physically active (76%25) compared with adults with asthma aged 45 to 64 (60%25) and 18 to 44 (50%25), with adults with asthma aged 45 to 64 more likely to be insufficiently physical active compared with adults with asthma aged 18 to 44. People with asthma aged 18 to 44 were less likely to be obese (35%25) compared with people with asthma aged 45 to 64 (48%25) and 65 and over (49%25).

Note: Overweight and obese are based on BMI for persons whose height and weight was measured and imputed. In 2017–18, 33.8% of respondents aged 18 years and over did not have a measured BMI. For these respondents, imputation was used to obtain BMI. For more information see Appendix 2: Physical measurements in the 2017–18 National Health Survey [4].

Source: AIHW analysis of ABS 2019 [5] (Data table).

Data notes

This analysis is based on people aged 18 and over. This age group was selected due to the available data about risk factors in the ABS National Health Survey (NHS) and to ensure consistency with other AIHW risk factor reports [17, 18].

The risk factor data presented here were obtained at one point in time, based on self-reported data from the NHS (with the exception of BMI, which was measured). 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 (and measured) risk factors and asthma. Risk factors present at the time of the survey may or may not have contributed to the presence of asthma. Similarly, the presence of asthma may not be directly related to the number of risk factors a person has.

The risk factor definitions used in the ABS 2017–18 National Health Survey are described below in Box 1.

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

Smoker status

Refers to the frequency of smoking of tobacco, including manufactured (packet) cigarettes, roll-your-own cigarettes, cigars and pipes, but excluding chewing tobacco, electronic cigarettes (and similar) and smoking of non-tobacco products. Categorised as:

Current daily smoker

A respondent who reported at the time of interview that they regularly smoked one or more cigarettes, cigars or pipes per day.

Current smoker – Other (occasional)

A respondent who reported at the time of interview that they smoked cigarettes, cigars or pipes, less frequently than daily.

Ex-smoker

A respondent who reported that they did not currently smoke, but had regularly smoked daily, or had smoked at least 100 cigarettes, or smoked pipes, cigars, etc at least 20 times in their lifetime; and

Never smoked

A respondent who reported they had never regularly smoked daily, and had smoked less than 100 cigarettes in their lifetime and had smoked pipes, cigars, etc less than 20 times.

Source: ABS 2018. National Health Survey: Glossary, 2017–18 [19].

Physical activity

Australia’s Physical Activity and Sedentary Behaviour Guidelines (the Guidelines) are a set of recommendations outlining the minimum levels of physical activity required for health benefits, as well as the maximum amount of time one should spend on sedentary behaviours to achieve optimal health outcomes [20]. Please see the Physical activity web topic page for more information.

In 2017–18, the ABS National Health Survey collected information for the first time on physical activity at work. Therefore all results for adults include physical activity at work.

Based on the guidelines, insufficient physical activity is defined as:

  • Adults aged 18–64 who did not complete 150 minutes of moderate to vigorous physical activity across 5 or more days in the last week
  • Adults aged 65 and over who did not complete at least 30 minutes of physical activity per day on 5 or more days in the last week.

For the purpose of calculating activity time, vigorous activity time is multiplied by a factor of two.

Muscle strengthening activities are not included in this analysis.

Source: AIHW 2019. Insufficient physical activity web report [21].

Body mass index

Body Mass Index (BMI) is a simple index of weight-for-height that is commonly used to classify underweight, normal weight, overweight and obesity. It is calculated from height and weight information, using the formula weight (kg) divided by the square of height (m). To produce a measure of the prevalence of underweight, normal weight, overweight or obesity in adults, BMI values are grouped according to the table below.

Category

Range

Underweight

Less than 18.50

Normal range

18.50 —24.99

Overweight

25.00 — 29.99

Obese I

30.00 — 34.99

Obesity class II

35.00 — 39.99

Obesity class III

40.00 or more

In 2017─18, 33.8% of respondents aged 18 years and over did not have a measured BMI. For these respondents, imputation was used to obtain BMI [22].

Sources: ABS 2018. National Health Survey: Glossary, 2017–18 [19]; ABS 2019. National Health Survey: Users’ Guide, 2017–18 [22].

References

  1. Beasley R, Semprini A & Mitchel EA 2015. Risk factors for asthma: is prevention possible? Lancet 386:1075-85.
  2. The Global Initiative for Asthma (GINA) 2019. Pocket guide for asthma management and prevention  (for adults and children older than 5 years). Viewed 1 May 2019.
  3. National Asthma Council Australia. Australian Asthma Handbook, Version 2.0. National Asthma Council Australia, Melbourne, 2019. Viewed 1 May 2019.
  4. Australian Bureau of Statistics (ABS) 2018. National Health Survey: First Results, 2017–18. ABS Cat. no. 4364.0.55.001. Canberra: ABS.
  5. ABS 2019. Microdata: National Health Survey, 2017-18, detailed microdata, DataLab. ABS cat no. 4324.0.55.001. Canberra: ABS. Findings based on AIHW analysis of ABS microdata.
  6. Mitchell E, Beasely R, Bjorksten B, Crane J, Garcia-Marcos L, Keil U et al. 2012. The association between BMI vigorous physical activity and television viewing and the risk of symptoms of asthma, rhinoconjunctivitis and eczema in children and adolescents: ISAAC Phase Three. Clinical & Experimental Allergy 43.
  7. Gilliland FD, Islam T, Berhane K, Gauderman WJ, McConnel R, Avol E, et al. Regular smoking and asthma incidence in adolescents. American Journal of Respiratory Critical Care Medicine 2006; 174: 1094-100
  8. Osborne ML, Pedula KL, O'Hollaren M, Ettinger K, Stibolt T, Buist AS, et al. 2007. Assessing future need for acute care in adult asthmatics: the Profile of Asthma Risk Study: a prospective health maintenance organization-based study. Chest; 132:1151-61.
  9. Tomlinson JE, McMahon AD, Chaudhuri R, Thompson JM, Wood SF, Thomson NC. 2005. Efficacy of low and high dose inhaled corticosteroid in smokers versus non-smokers with mild asthma. Thorax; 60(4):282-7.
  10. Lazarus SC, Chinchiili VM, Rollings NJ, Boushy HA, Cherniak R, Craig TJ, et al. 2007. Smoking affects response to inhaled corticosteroids or leuktriene receptor antagonists in asthma. American Journal of Respiratory Critical Care Medicine; 175(8):783-90.
  11. Adeniyi FB, Young T. 2012. Weight loss interventions for chronic asthma. Cochrane Database of Systematic Reviews; 7.
  12. Juel CT, Ali Z, Nilas L & Ulrik CS. 2012. Asthma and obesity: does weight loss improve asthma control? a systematic review. Journal of Asthma and Allergy; 5:21-26. 
  13. Ford ES. 2005. The epidemiology of obesity and asthma. Journal of Allergy and clinical Immunology; 115(5): 897-909.
  14. Kim S, Sutherland ER & Gelfand EW. 2014. Is there a link between obesity and asthma? Allergy, Asthma & Immunology Research; 6(3): 189-195.
  15. 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. 
  16. Royal Australian College of General Practice (RACGP) 2014. Supporting smoking cessation: a guide for health professionals. Melbourne: The Royal Australian College of General Practitioners. 
  17. Australian Institute of Health and Welfare (AIHW) 2015. Cardiovascular disease, diabetes and chronic kidney disease—Australian facts: risk factors. Cardiovascular, diabetes and chronic kidney disease series no. 4. Cat. no. CDK 4. Canberra: AIHW.
  18. AIHW 2013. Risk factors contributing to chronic disease. Cat No. PHE 157. Canberra: AIHW.
  19. Australian Bureau of Statistics (ABS) 2018. National Health Survey: Glossary, 2017–18. Viewed 1 May 2019.
  20. Department of Health 2019. Australia's Physical Activity and Sedentary Behaviour Guidelines and the Australian 24-Hour Movement Guidelines. Canberra: DoH. Viewed 5 June 2019.  
  21. AIHW 2019. Insufficient physical inactivity: Web report.
  22. ABS 2019. National Health Survey: Users’ Guide, 2017─18. Viewed 5 June 2019.