Elsevier

The Lancet

Volume 386, Issue 9998, 12–18 September 2015, Pages 1075-1085
The Lancet

Series
Risk factors for asthma: is prevention possible?

https://doi.org/10.1016/S0140-6736(15)00156-7Get rights and content

Summary

Asthma is one of the most common diseases in the world, resulting in a substantial burden of disease. Although rates of deaths due to asthma worldwide have reduced greatly over the past 25 years, no available therapeutic regimens can cure asthma, and the burden of asthma will continue to be driven by increasing prevalence. The reasons for the increase in asthma prevalence have not been defined, which limits the opportunities to develop targeted primary prevention measures. Although associations are reported between a wide range of risk factors and childhood asthma, substantiation of causality is inherently difficult from observational studies, and few risk factors have been assessed in primary prevention studies. Furthermore, none of the primary prevention intervention strategies that have undergone scrutiny in randomised controlled trials has provided sufficient evidence to lead to widespread implementation in clinical practice. A better understanding of the factors that cause asthma is urgently needed, and this knowledge could be used to develop public health and pharmacological primary prevention measures that are effective in reducing the prevalence of asthma worldwide. To achieve this it will be necessary to think outside the box, not only in terms of risk factors for the causation of asthma, but also the types of novel primary prevention strategies that are developed, and the research methods used to provide the evidence base for their implementation. In the interim, public health efforts should remain focused on measures with the potential to improve lung and general health, such as: reducing tobacco smoking and environmental tobacco smoke exposure; reducing indoor and outdoor air pollution and occupational exposures; reducing childhood obesity and encouraging a diet high in vegetables and fruit; improving feto-maternal health; encouraging breastfeeding; promoting childhood vaccinations; and reducing social inequalities.

Introduction

Asthma is one of the most common chronic diseases in the world, resulting in a substantial worldwide burden of disease.1 The temporal trend of increasing prevalence of asthma over the past 60 years (figure 1) is likely to continue as transitional communities progressively adopt lifestyles of high-income countries and become urbanised.2 Over recent decades the public health priority has been to improve the assessment and management of asthma,3 resulting in a 42% reduction in age-standardised asthma death rates worldwide between 1990 and 2013.4 However, as no therapeutic regimen can cure asthma, such approaches will always have their limitations. As a result, it is necessary to gain a better understanding of the factors that cause asthma, and to develop alternative public health and pharmacological primary preventive measures that are effective in reducing the prevalence of asthma worldwide. In this Series paper, we review current evidence for the risk factors for asthma and its primary prevention, and propose priorities for research that will lead to the implementation of effective primary intervention strategies.

Section snippets

Can asthma be prevented?

It is reasonable to suggest that asthma prevention is possible, because standardised international epidemiological studies in both children and adults have shown that some populations have very low asthma symptom prevalence rates.5, 6 These surveys have identified worldwide patterns of asthma symptom prevalence that are not accounted for by existing knowledge of the causation of asthma,5, 6 but they do provide data on risk factors on which primary prevention measures might be based. However,

Risk factors

A comprehensive list of risk factors for the development of asthma in childhood is presented in table 2. Age is an important consideration in respect of the different phenotypes of childhood wheeze. Children with persistent and late onset wheeze, but not those with transient forms of wheezing up to 3 years of age, have greater risk of having persistent childhood asthma.9 These findings suggest that for any primary prevention strategy to target those at risk of persistent childhood asthma, it

Primary intervention studies

At least 42 RCTs have assessed primary prevention strategies in childhood asthma (table 3). In addition to the findings relating to efficacy, primary preventive measures need to be assessed by several other criteria. These include consideration of specific interventions in populations with different lifestyles versus a global approach, identification of responders through clinical, immunological or genetic markers, applicability to an entire population versus those at high risk, efficacy in

Future research

Further longitudinal birth cohort studies in large populations that investigate novel and established risk factors, biomarkers of risk and asthma phenotypes, and genetic and environmental interactions are needed. The findings from such studies will inform future RCTs of primary prevention interventions in at-risk infants. It is likewise necessary to think outside the box in designing RCTs that might best assess future strategies based on advances in knowledge (figure 2). Limitations of many of

Search strategy and selection criteria

We searched PubMed using “Asthma” and “Primary prevention”. We applied the filter for “clinical trial” and reviewed the results to isolate primary prevention trial reports. We searched Embase and World Health Organization Clinical Trials Registry with the terms “asthma” and “primary prevention” and reviewed the results for primary intervention trials and duplicates from PubMed. We searched the Cochrane Library database using the terms “Asthma” and “Primary prevention” and applying “trials”

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