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 3 days/week)
  • not taking preventer (inhaled corticosteroid) treatment regularly
  • frequent reliever use
  • major psychological or socioeconomic problems
  • smoking.

Common risk factors

Based on the 2014–15 National Health Survey (NHS), people with asthma were more likely to be physically inactive and/or obese, compared to 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, 2014–15

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 (see Box 1)

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

Selected risk factors

Smoking status

People with asthma were more likely to report having been a smoker in the past (see Figure 2):

  • 35.8% were ex-smokers (compared with 30.8% for people without asthma)
  • 47.5% had never smoked (compared with 53.2% for people without asthma).

However, for all ages combined, the proportion of current smokers was similar in those with (15.4%) and without asthma (14.4%) in the NHS 2014–15.

Tobacco use or exposure to environmental tobacco smoke are risk factors associated with the development of asthma. The interaction bbox1etween 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 [3], and smoking by a parent or child/adolescent is linked to asthma symptoms in adolescence [4].  

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 [5]. In people with asthma, smoking is also associated with a reduced effectiveness of inhaled corticosteroids [6, 7].    

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

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).

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.

Evidence suggests that sedentary behaviour (as measured by television viewing) is associated with asthma symptoms in children [3]. 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 [8].

Based on the 2014–15 NHS, people with asthma were less likely than people without asthma to report engaging in the recommended levels of physical activity. For adults (ages 18 and over) with asthma, 61.7% reported being physically inactive (this includes people who were inactive and insufficiently active) compared with 53.6% of those without asthma (Figure 3). That is, 38.3% of adults with asthma were sufficiently active for health, compared with 46.2% of adults without asthma.

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

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 asthma were 1.3 times as likely to be obese (by measured body mass index or BMI — see data notes) as people without asthma (35.6% with asthma compared with 27.0% 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 and obese often experience complications in treatment. For people who are overweight and obese, weight loss has been shown to reduce treatment complications and improve symptoms [9, 10]. There is evidence of an association between being obese and developing asthma; however, the causative mechanisms between body weight and asthma are not currently well understood [11, 12].

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

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 asthma

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

The prevalence of smoking in people with asthma decreased with age. People aged 18–44 and 45–64 with asthma were more likely to report current daily smoking (17.7% and 16.8%, respectively) than those aged 65 and over (6.5%)(Figure 5). The lower smoking rates among older Australians may be due to greater health awareness, or to quitting after the development of respiratory symptoms. Smoke free laws, tobacco price increases and greater exposure to mass media campaigns may also contribute [13]. 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 [14].

Physical inactivity and overweight and obesity in the general population increases with age, however this increase is more pronounced among those with asthma [15]. Among people with asthma, 52.2% of those aged 18–44 were physically inactive, compared with 73.3% of those aged 65 and over. Among the general population, 49.4% of those aged 18–44 were physically inactive, compared with 64.8% of those aged 65 and over.

Among those with asthma aged 18–44, 58.4% were overweight or obese, compared with 76.8% of those aged 65 or over. Among the general population aged 18–44, 54.0% were overweight or obese compared with 72.2% for those aged 65 and over.

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

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 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 [16, 17].

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 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 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. 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 [18].

References

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  2. The Global Initiative for Asthma (GINA) 2015. Pocket guide for asthma management and prevention (1.8MB PDF) (for adults and children older than 5 years). Viewed 27 May 2016.
  3. 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.
  4. 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
  5. 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.
  6. 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.
  7. 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.
  8. National Asthma Council Australia 2015. Australian asthma handbook, version 1.1. Melbourne: NACA. Viewed 22 February 2016.
  9. Adeniyi FB, Young T. 2012. Weight loss interventions for chronic asthma. Cochrane Database of Systematic Reviews; 7.
  10. 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. 
  11. Ford ES. 2005. The epidemiology of obesity and asthma. Journal of Allergy and clinical Immunology; 115(5): 897-909.
  12. Kim S, Sutherland ER & Gelfand EW. 2014. Is there a link between obesity and asthma? Allergy, Asthma & Immunology Research; 6(3): 189-195.
  13. 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. 
  14. Royal Australian College of General Practice (RACGP) 2014. Supporting smoking cessation: a guide for health professionals (PDF). Melbourne: The Royal Australian College of General Practitioners. 
  15. Australian Bureau of Statistics (ABS) 2015. National Health Survey: First Results, 2014–15. ABS Cat. no. 4364.0.55.001. Canberra: ABS.
  16. 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.
  17. AIHW 2013. Risk factors contributing to chronic disease. Cat No. PHE 157. Canberra: AIHW.
  18. ABS 2013. Australian Health Survey: Users’ Guide, 2011–13. Viewed 16 August 2015.