Incurable lung disease levels on the rise

Rates of incurable lung diseases are rising the BBC reported today. Tests of 9,500 adults over the age of 40 found that 1 in 10 people had chronic obstructive pulmonary disease (COPD). Rates are also set to rise further as the population ages, according to the study on which this report is based.

The study involving participants across 12 countries found that the levels of COPD are higher than previous studies had claimed, with 11.8% of men and 8.5% of women  found to have moderate or higher stage COPD. The researchers also reported that the risk of the disease doubles every 10 years that a person smokes over the age of 40.

The study is well-conducted research that provides new data on the worldwide prevalence of COPD. However, care must be taken when making any conclusions about the disease’s prevalence in countries other than those studied.

Although the BBC’s headline stated that lung disease rates are “on the rise”, the study did not measure if COPD rates are increasing, but only looked at how many people had the disease at one point in time. The interpretation that there are now more people with lung disease than before is based on a comparison of these results with previous studies. The increased levels shown in the  results could have been caused by differences in the way that the studies were carried out or other interfering factors.

Where did the story come from?

Sonia Buist of Oregon Health Sciences University, Portland, and colleagues of other research institutes in the US, UK, Australia, Norway and Poland carried out this research. The research was funded by grants from several organisations including ALTANA, Aventis, AstraZeneca, Chiesei, Merck, Pfizer, University of Kentucky. The study was published in the peer-reviewed medical journal, The Lancet .

What kind of scientific study was this?

This was a multinational cross-sectional study designed to estimate the worldwide prevalence of COPD and its associated risk factors (including smoking, years spent in a dusty job, history of TB etc), and to see how this varied across countries.

This research studies the results from sites in 12 countries that had completed data collection by the end of December 2006. Each country tested about 600 adults aged over 40 years. The groups had equal numbers of male and female participants randomly selected from areas where the population exceeded 150,000.

The participants were each interviewed and completed a questionnaire on their health status, respiratory symptoms and exposure to risk factors.

The participants then carried out a spirometry test, that measures the capacity of the lungs and which shows the extent of restrictive or obstructive lung disease. The test was carried out both before and after administering inhaled bronchodilator drugs, to see whether any difference was made by dilating the lung air passages (an indication of obstructive lung disease).

Estimates were made of population prevalence and statistical methods were used to adjust for how risk factors such as smoking may contribute.

What were the results of the study?

An average across all the countries showed that 10.1% of people (11.8% for men, 8.5% for women) had COPD of severity stage 2 or over, according to the internationally accepted standard, GOLD. The Global Initiative for COPD (GOLD) criteria has five stages of COPD, with stage 5 being the worst. Prevalence by country actually varied widely, particularly in women.

The researchers found that levels of COPD increased with age and with the amount a person smoked. The researchers said that a difference in COPD prevalence between men and women was partly explained by differences in smoking patterns.

What interpretations did the researchers draw from these results?

The researchers conclude that the overall prevalence of COPD seems to be higher than reported in previous studies.

They say that “although age and smoking are strong contributors to COPD, they do not fully explain variations in disease prevalence – other factors also seem to be important”. The researchers interpret this to indicate the need for a better understanding of the risk factors of COPD.

What does the NHS Knowledge Service make of this study?

This study was generally well conducted and adds useful information to our understanding of the prevalence and risk factors associated with COPD. However there are several points to consider:

• The figures for the overall prevalence of COPD are taken from the combined results of 12 countries, all with varied individual COPD rates. There was also great variation in the number of people sampled in each country. This could affect the accuracy of the results (response rates varied from 14% in the US site to 87% in China). Care should therefore be taken when extrapolating these results to another country, such as the UK.
• Smoking and increasing age are well established risk factors in COPD. There may be other factors that weren't considered. For instance, a history of lung disease, such as tuberculosis, may also have an association.
• Although standard spirometry methods and set criteria to diagnose COPD across countries were used, there may have been unavoidable differences in accuracy of measurements and diagnosis between countries.
• We must remember that the interpretation that rates of COPD are “increasing” is based on comparing the results of this study with the results of other studies whose methods we have not looked at. This study was only designed to tell us how many people have the condition at one point in time.

Sir Muir Gray says…

As someone old enough to remember the terrible fogs and smogs of the 1950s, when only the trams could move because visibility was just one or two yards, I rejoice that, chronic air pollution, one major cause of COPD in the UK, was removed by the Clean Air Acts of the 1950s and 60s

I once asked a tough Glaswegian  with a broken leg if he had any other health problem when taking his routine medical history before an operation. “No doctor“ he replied confidently. I then asked if he had a cough; “oh yes doctor” he replied “ I cough for 30 minutes every morning, you have to get the glut up”.

That was normal in the Glasgow of my youth, and my lungs bear some of the scars. Now, in the UK, smoking is the number one cause by a long way. Debates about prevalence are interesting, but the most important thing to bear in mind is that COPD is a big problem, one of the big 50, and it is not well managed.