Cigarette smoking continues to be the single most important preventable health risk in the developed world. The 2007 Slán survey found that 29% of Irish adults are current smokers (defined as ‘smoking every day’, or ‘some days’, and having ‘smoked at least 100 cigarettes’ during their lifetime). 

Moreover, smoking rates among young women, particularly those in lower socioeconomic groups, are substantially higher. In Ireland, cigarette smoking accounts for approximately 6,000 premature deaths annually. This review explores the link between cigarette smoking and pulmonary disease and highlights interventions to tackle this enormous burden on Irish society.

Lung cancer

The link between tobacco smoke and lung cancer has long been suspected, but it was the landmark epidemiological study by Doll and Hill published over 60 years ago that confirmed the association. Indeed, the indisputable aetiological role of cigarette smoking in the pathogenesis of lung cancer is among the most extensively studied causal relationships in biomolecular research. Lung cancer is the principal cause of cancer-related morbidity and mortality worldwide. In Ireland, approximately 1,800 new cases of lung cancer are diagnosed each year, and the disease is now the commonest cause of cancer mortality in both men and women. However, the disease is almost entirely preventable as accumulated epidemiologic data indicate that at least 90% of cases occur in current or former smokers, with duration of smoking the principal determinant of risk. The dramatic increase in the incidence of lung cancer observed during the latter half of the last century closely mirrors prior patterns of tobacco consumption, with a lag time of approximately 20 years. Although the peak of lung cancer appears to have passed in males in line with changing smoking trends, epidemiological research indicates that peak rates in females have not yet been reached. 

Indeed, the incidence and mortality rates for Irish women are among the highest in Europe. Approximately one-third of lung cancer patients have evidence of metastatic disease at time of initial presentation. As a result, and despite significant advances in diagnostic techniques and therapeutic approaches, the overall five-year survival rates for patients remain poor and has shown only marginal improvement over the past three decades. There is no approved screening test for lung cancer in Ireland, though recently published data indicate that screening with yearly low-dose chest computed tomography (CT) in current or former smokers confers a mortality benefit. 

The establishment of the National Cancer Control Programme in Ireland has led to the reorganisation of lung cancer services with a shift from a multi-institutional to a national model of care, with the aim of implementing improved standards of access to and quality of diagnostic and treatment services for lung cancer patients. It is hoped that this will in turn lead to improvements in patient outcomes.

Chronic obstructive pulmonary disease 

Chronic obstructive pulmonary disease (COPD) is a common but preventable disorder characterised by airflow limitation that is not fully reversible and associated with an exaggerated chronic inflammatory response to noxious gases or particles. It is projected to become the fourth-leading cause of death worldwide by 2030 and is associated with considerable economic burden in Ireland. At least 440,000 Irish persons have COPD, with as many as half of all cases undiagnosed. The most important modifiable risk factor for COPD is cigarette smoking, with data to suggest that half of all smokers will eventually develop the disorder. 

The disease shows a clear male predominance because of historically higher cigarette smoking rates in men, although the gradual narrowing of the smoking gender gap will see a continued increase in prevalence rates in females. The cardinal symptoms reported by patients are insidious onset of progressive dyspnoea and reduced exercise capacity, the predictable consequences of a progressive impairment in lung function. A clear dose-dependent relationship between the extent of smoking and the magnitude of the decrease in the volume of air exhaled within the first second of the forced expiratory manoeuvre (FEV1) has been established. Although pharmacological therapies improve patient symptoms, health status and exercise capacity, and can attenuate the severity and frequency of episodes of acute worsening of COPD (exacerbations), only smoking cessation has been consistently shown to significantly slow the rate of decline in lung function. Accordingly, all patients with COPD who smoke should be counselled as to the merits of stopping smoking. 

Asthma

Asthma is a chronic inflammatory disorder associated with airway hyperresponsiveness and reversible airflow obstruction. Asthma control, or lack thereof, is influenced by a number of potentially modifiable environmental factors, including cigarette smoking. Compared to non-smokers, patients with asthma who smoke frequently have worse symptoms, poorer asthma control, more rapid worsening of lung function and are at an increased risk of hospitalisation. 

Moreover, inhaled corticosteroids, the cornerstone of treatment in those with persistent symptoms, are globally less effective in smokers with asthma. The exact mechanisms that account for this attenuated response to corticosteroids remain poorly understood, but probably reflect associated noneosinophilic airway inflammatory changes, alteration of the glucocorticoid receptor function and irreversible airway remodelling. 

Interstitial lung disease

In recent years, a firm association between smoking and several interstitial lung diseases has been established on the weight of mounting epidemiological evidence. Idiopathic pulmonary fibrosis (IPF; previously known as cryptogenic fibrosing alveolitis) is a progressive and usually fatal disease of unknown cause characterised by insidious onset of dyspnoea and cough. There is no effective treatment for IPF. The aetiology is likely multifactorial, with numerous inherited and acquired risk factors implicated. However, a key role for cigarette smoking is supported by the observation that approximately 75% of patients have a significant smoking history. 

Respiratory bronchiolitis-associated interstitial lung disease (RB-ILD) is a distinct form of diffuse parenchymal lung disease that has a near-universal association with cigarette smoking. Cough and dyspnoea are the predominant symptoms; abnormal pulmonary function is usual, with obstructive and restrictive ventilatory defects equally common. Though high-resolution chest CT (HRCT) may show characteristic suggestive findings, surgical biopsy is often required for definitive diagnosis. The cornerstone of management is smoking cessation, either alone or in conjunction with systemic anti-inflammatory agents. Desquamative interstitial pneumonia (DIP) is a rare form of interstitial lung disease characterised pathologically by widespread accumulation of macrophages in alveolar spaces. Most published series have reported a history of smoking in affected patients, though other genetic, acquired and environmental factors play an aetiological role in some cases of the disease, since cases have been described in children. Interestingly, histological appearances of DIP show similarities to RB-ILD, with some investigators suggesting the two disorders represent a continuum of the same process. 

As is the case for RB-ILD, the key components of management of DIP are smoking cessation and corticosteroid therapy. Pulmonary Langerhans cell histiocytosis (PLCH) is a diffuse bronchiolocentric inflammatory disorder characterised by proliferation of specific histiocytes (Langerhans cells) that is most commonly observed in young adults and almost exclusively in cigarette smokers. Widespread lung cyst formation and vascular damage results in progressive exercise limitation and irreversible respiratory failure in the most severe form. There is no approved therapy for PLCH; however, stopping smoking leads to stabilisation of symptoms in most patients.

Tobacco control

Coherent and sustained strategies to both discourage initiation of smoking among adolescents and facilitate smoking cessation in current smokers are required in order to impact on the prevalence rates of smoking and thereby reduce the burden of tobacco-related lung disease in Ireland. Indeed, smoking cessation interventions are among the most cost-effective of all healthcare interventions and should be emphasised irrespective of patient age. Data from cohort and case-control studies clearly demonstrate that the risk of COPD, lung cancer and other smoking-associated lung diseases is reduced among individuals who stop smoking compared to continuing smokers. 

Although the implementation of a complete ban on smoking in public places in Ireland in 2004 was principally to protect the health of workers from the deleterious effects of environmental tobacco smoke, the encouragement of smoking cessation is broadly accepted as an additional rationale. 

Conclusion

Reduction in smoking prevalence is key to impacting on the burden of respiratory disease in Ireland. Sustained smoking cessation confers a lower risk of developing lung cancer and chronic lung disease. Early introduction of approved pharmacotherapy, in conjunction with appropriate support, in motivated patients who smoke should be routinely offered.