Poverty, not smoking, linked to COPD mortality

An international study shows that national mortality rates for chronic obstructive pulmonary disease (COPD) do not correlate well with the prevalence of smoking in low-income countries but do show a strong inverse correlation with wealth.

Additionally, analysis of data from 22 sites in the Burden of Obstructive Lung Disease (BOLD) study indicated that cigarette smoking prevalence is a good predictor for airflow obstruction.

Peter Burney, from Imperial College London, UK, and colleagues report a wide range of rates of airflow obstruction (postbronchodilator forced expiratory volume in 1 second [FEV1] to forced vital capacity [FVC] ratio < lower limit of normal [LLN]) and spirometric restriction (postbronchodilator FVC

The team found that while rates of mortality from COPD correlated strongly with the prevalence of spirometric restriction, they did not correlate well with airflow obstruction.

However, using COPD mortality data from 170 countries, they show that it has a strong, inverse correlation with gross national income (GNI). In particular, when annual GNI fell below US$ 15,000 (€ 11,000) per capita, rates of COPD mortality rose rapidly. By contrast, in the 135 countries falling under this low-income threshold, there was no clear association between the prevalence of smoking and COPD mortality.

There was also a strong association between the prevalence of spirometric restriction and lower GNI, which again rose rapidly when GNI fell below the threshold.

Despite the lack of association in low-income countries, overall, there was a significant negative correlation between smoking prevalence and COPD mortality when all countries were analyzed, and when the researchers looked at data from the 22 BOLD sites.

Writing in Thorax, Burney et al note that the strong effect of poverty on COPD mortality has previously been reported, but they say that is international impact has not been explored.

“The lack of association between smoking prevalence and mortality from ‘COPD’ is explained by the inverse association between airflow obstruction and smoking,” the researchers comment. They suggest that that FVC may be low in poor countries due to ethnic differences, with the greatest relationship between income and the measurement in the most ethnically diverse populations.

They add, however, that environmental factors probably play the largest role in mediating this relationship, including low birth weight, air pollution, poor diet, exposure to early infections, and biomass fuel.

Commenting on the strong association between spirometric restriction and COPD mortality, they note that “evidence from the USA shows that the FVC is a much stronger determinant of survival than the FEV1/FVC ratio.”

They add: “It is unlikely that the high mortality attributed to ‘COPD’, particularly in low-income countries, is associated with chronic airflow obstruction. It is much more likely to be associated with spirometric restriction.

“These analyses challenge us to rethink our notions and beliefs about the origins and significance of chronic lung disease and its prominent role as a major cause of death in low-income countries.”

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