This review surveys the data on the increase in the prevalence of asthma in recent decades and finds evidence of a plateau in many Western countries. The authors examine the evidence of possible causal relations to factors such as air pollution, obesity, diet, and exposure to infections, antibiotics, and allergens, including exposures at very young ages. The most strongly supported preventive measure is the avoidance of passive and active exposure to smoke.

The asthma epidemic.

Asthma prevalence has increased very considerably in recent decades such that it is now one of the commonest chronic disorders in the world. Recent evidence from epidemiological studies, however, suggests that the prevalence of asthma may now be declining in many parts of the world, which, if true is important for health service planning and also because this offers the possibility of generating and testing new aetiological hypotheses. Our objective was to determine whether the prevalence of asthma is declining worldwide. We undertook a systematic search of EMBASE, Medline, Web of Science and Google Scholar, for high quality reports of cohort studies, repeat cross-sectional studies and analyses of routine healthcare datasets to examine international trends in asthma prevalence in children and adults for the period 1990-2008. There were 48 full reports of studies that satisfied our inclusion criteria. The large volume of data identified clearly indicate that there are, at present, no overall signs of a declining trend in asthma prevalence; on the contrary, asthma prevalence is in many parts of the world still increasing. The reductions in emergency healthcare utilization being reported in some economically developed countries most probably reflect improvements in quality of care. There remain major gaps in the literature on asthma trends in relation to Africa and parts of Asia. There is no overall global downward trend in the prevalence of asthma. Healthcare planners will for the foreseeable future, therefore, need to continue with high levels of anticipated expenditure in relation to provision of asthma care.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1398-9995.2009.02244.x

Is the prevalence of asthma declining? Systematic review of Epidemiological studies

Trends in asthma indicators from population surveys (prevalence) and routine statistics (primary care, prescriptions, hospital admissions and mortality) in the UK were reviewed from 1955 to 2004. The prevalence of asthma increased in children by 2 to 3-fold, but may have flattened or even fallen recently. Current trends in adult prevalence are flat. The prevalence of a life-time diagnosis of asthma increased in all age groups. The incidence of new asthma episodes presenting to general practitioners increased in all ages to a plateau in the mid 1990s and has declined since. During the 1990s, the annual prevalence of new cases of asthma and of treated asthma in general practice showed no major change. Hospital admissions increased from the early 1960s, more so in children, until the late 1980s and have fallen since. Asthma mortality showed two waves, a shorter and more intense one in the mid 1960s and a longer and less intense one in the late 1970s and early 1980s. The relative roles of diagnostic transfer, coding changes, medical care and epidemiological factors are discussed.

https://thorax.bmj.com/content/thoraxjnl/62/1/85.full.pdf

50 years of asthma: UK trends from 1955 to 2004

Obesity is a worldwide epidemic and is known to increase the risk of cardiovascular disease, type 2 diabetes, and certain forms of cancer. In addition, obesity is now recognized as an important risk factor in the development of several respiratory diseases. Of these respiratory diseases, it has already been well established that obesity can lead to obstructive sleep apnea (OSA) and obesity-hypoventilation syndrome (OHS). More recent data suggest that the prevalence of wheezing and bronchial hyper-responsiveness, two symptoms often associated with asthma, are increased in overweight and obese individual. Indeed, epidemiological studies have reported that obesity is a risk factor for the development of asthma. Furthermore, a number of studies indicate that obesity is also associated with a higher risk of developing deep vein thrombi, pulmonary emboli, pulmonary hypertension, and pneumonia. Finally, weight reduction has been shown to be effective in improving the symptoms and severity of several respiratory diseases, including OSA and asthma. Thus, overweight and obese patients should be encouraged to lose weight to reduce their risk of developing respiratory diseases or improve the course of pre-existing conditions.

https://journals.sagepub.com/doi/pdf/10.1177/1479972308096978

Obesity and respiratory diseases

Obesity and asthma prevalence have been increasing over the past decade. Epidemiological evidence demonstrates that obesity results in an increased risk of developing incident asthma. Even modest levels of increased weight increase asthma risk. Recently published data suggest that obese asthma patients may represent a distinct phenotype of asthma. Obese asthma patients demonstrate increased asthma severity, as indicated by increased exacerbations and decreased asthma control; however, they do not appear to have increased airway cellular inflammation. It seems likely that obesity does not contribute to asthma through conventional Th type 2-mediated inflammatory pathways but, rather, through separate mechanisms that are specific to the obese state. This may explain the variable responses of obese asthma patients to conventional asthma therapies, specifically, relative corticosteroid resistance. Small studies suggest improvements in the disease with weight loss in obese asthma patients, and other interventions to target asthma in obese individuals need to be investigated. Several postulated mechanisms for the occurrence of this distinct phenotype have been postulated: 1) the presence of comorbidities, such as gastroesophageal reflux disease and sleep disordered breathing, 2) systemic inflammation associated with obesity (with elevated levels of circulating cytokines, such as IL-6 and TNF-α), 3) increased oxidative stress, and 4) hormones of obesity, such as adiponectin, leptin, and resistin. Although the mechanisms underlying obesity in asthma require further investigation, obesity plays a major role in the asthma epidemic and likely results in a distinct phenotype of the disease.

Does obesity produce a distinct asthma phenotype

Objective To determine changes in childhood and parental asthma prevalence in Merseyside between 1991 and 1998.Methods Three standardized cross-sectional respiratory health surveys using a parent-completed questionnaire were completed in 1991 (n = 1171), 1993 (n = 2368) and 1998 (n = 1964) amongst primary school children (5-11 years) attending the same 10 schools. The main outcome measures were prevalence of reported doctor diagnosed asthma, the symptom triad of cough, wheeze and breathlessness (C+W+B+) and parental asthma.Results Significant changes in prevalence for all respiratory variables occurred between 1991 and 1998, except for the symptom triad C+W+B+. Between 1991 and 1998 the prevalence of reported doctor diagnosed asthma increased from 17.7 to 29.8 per cent (p < 0.001), history of wheezing increased from 22.5 to 29.4 per cent (p < 0.001). The symptom triad of C+W+B+ changed from 9.6 to 9.9 per cent (p = 0.78). Childhood reported hospital admissions for respiratory illness increased from 5.5 to 10.7 per cent (p < 0.001). Paternal asthma increased from 6.5 per cent in 1991, to 8.6 per cent in 1998 (p = 0.031), and maternal asthma almost doubled in the same period from 6.6 to 11.2 per cent (p < 0.001). Children living in poorer areas (Townsend score 8-11) were more likely to have doctor diagnosed asthma (OR = 2.99, 95 per cent Cl, 2.06 to 4.33) and C+W+B+ (OR = 2.17, Cl 1.13 to 4.18). Childhood obesity was significantly associated with increased risk of both doctor diagnosed asthma (OR = 1.74, 95 per cent Cl 1.29 to 2.37) and C+W+B+ (OR = 1.88, 95 per cent Cl, 1.21 to.90).Conclusion A rising prevalence of reported doctor diagnosed asthma, but not C+W+B+ was observed during the 1990s in a low socio-economic area of Liverpool. Asthma prevalence was related to socio-economic deprivation and was associated with obesity. The rising prevalence of reported doctor diagnosed asthma is likely to be attributable to several factors including changes in diagnostic labelling and the distribution of factors related to socio-economic status.

/pdf/trends-in-childhood-and-parental-asthma-prevalence-in-uh5epflph6.pdf

Trends in childhood and parental asthma prevalence in Merseyside, 1991-1998.

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Trends in childhood and parental asthma prevalence in Merseyside, 1991-1998.