5.8.4. Risk factors

Active and passive tobacco smoking are major risk factors for COPD. Occupational factors and indoor-outdoor pollution from biomass fuel are other well recognized risk factors.

Among 1711 middle-aged men of two rural Finnish cohorts, which were monitored within the framework of the Seven Countries Study, involving US, Finland, Netherlands, Italy, Greece, Japan and Croatia – Serbia (former Jugoslavia), the 30-year cumulative incidences of chronic bronchitis and COPD were assessed at 42% and 32%, respectively, in continuous smokers, and to 22% and 12% in never-smokers (Pelkonen et al, 2006). During the follow-up, subjects with chronic bronchitis showed 252 mL lower forced expiratory volume than subjects without it.

In another study performed in Copenhagen, Denmark, 8045 men and women aged 30-60 with normal lung function at baseline were followed for 25 years (Lokke et al, 2006). Abnormal lung function ranged from 4% for male never smokers (9% in women) to 41% for male continuous smokers (31% in women). The 25-year cumulative incidence of moderate and severe COPD was 24.3 % in continuous smokers, compared to 1% in never smokers, with no significant differences between men and women. The risk of developing COPD decreases with the decreasing duration of smoking.

A comparison of results on the correlation of COPD with the smoking habit is presented in Figure 5.8.3.

Figure 5.8.3. Incidence rates of COPD and smoking habit in Nordic European Countries.

A study by Lundback (2003) showed that age and smoking were the two major determinants, in a multivariate analysis including age, gender, smoking habits, family history of obstructive airway disease and socioeconomic group as COPD determinants. In the analysed population, aged 46 to 77, odds ratio associated with smoking more than 5 cigarettes per day was about 8, compared to non-smokers. Prevalence of COPD reached 50% in elderly smokers.

Furthermore, COPD has usually been associated with the male gender (Siafakas et al, 1995). But a study by Soriano et al (2000) by means of a large database of medical practitioner records in the UK, showed that between 1990 and 1996 gender-related differences decreased, and COPD spread rapidly in 20-44 year old women. This was confirmed in the ECRHS study, which proved that the female gender was significantly affected by chronic cough and phlegm (odds ratio 1.22 compared to males) (Cerveri et al, 2003).

COPD has been usually considered as a disease affecting people over 50 years of age. This was contradicted in the ECRHS study: COPD is already present at the age of 20-45, with prevalence rates of 11.8% for the pre-clinical stage, when airway obstruction has not yet been developed (GOLD stage 0), 2.5 and 1.1% for GOLD stages I and II+, respectively (De Marco et al, 2004).

In a review of community or general population studies carried out in the United States, France, Poland, Italy, Norway, China, the Netherlands and Spain, it was concluded that occupational exposure contributes by about 10-20% to the burden of COPD (Balmes et al, 2003). Dusty environments were found to contribute by 10% in smokers and by 50% in never-smokers among Swedish construction workers (Bergahl et al, 2004). In the European Community Respiratory Health Survey (ECRHS) study high exposures to dusts and fumes increased the risk for chronic bronchitis from smoking by 160%. Neither a steeper decline of FEV₁ nor an increased prevalence of airway obstruction was observed in exposed individuals. Some increase in the incidence of chronic phlegm was found in individuals exposed to mineral dusts, gases and fumes (Zock et al, 2001; Sunyer et al, 2005).

The exact prevalence of COPD is variable across the available data, probably because of differences in the methods used for patients selection and classification. Despite that, COPD is strongly associated with ageing, and some factors allowing people to survive in old age, such as enhanced interventions for acute cardiovascular diseases, and acute infections, will result in higher COPD prevalence, morbidity, and mortality. In other words, as a result of the global population ageing, COPD is one of several chronic diseases that will become more frequent. These disorders will be better managed through particular care towards prevention and cost-effectiveness of intervention (Mannino 2007).