Poverty, height and lung disease

“People who develop chronic lung disease are more likely to be shorter in height than the general population,” BBC News reported. This story is based on a study of over a million people that investigated whether there is a link between adult height and chronic obstructive pulmonary disease (COPD). It found that people with COPD were 1.12cm shorter on average than the general population.

The researchers do not suggest that short stature causes COPD, but that it is a marker of social deprivation in childhood, which is historically linked with an increased risk of developing disease in adulthood.

The study used data from over a million people, and took into account their age, sex and social deprivation. However, it did not take into account smoking, which is the most important risk factor for COPD. If the researchers had taken this into account, then it would have been possible to see whether other aspects of social deprivation such as poor diet and environment are associated with COPD, as well as smoking.

Smoking remains the biggest risk factor for COPD. Quitting smoking reduces the risk of developing COPD, regardless of height, social class or age.

Where did the story come from?

Richard Hubbard, Professor of Respiratory Medicine at City Hospital, Nottingham, and medical student Katie Ward, carried out this research. The study was funded by the British Lung Foundation and published in the peer-reviewed Journal of Epidemiology and Community Medicine.

What kind of research was this?

This cross-sectional study investigated the association between adult height and COPD. Historically, shorter stature in adulthood has been linked to an increased risk of developing various diseases. Short stature itself is not thought to be a risk factor for COPD, but to be a marker of poor living conditions in childhood. The researchers wanted to see whether this link exists in the present day, now that general living conditions have improved.

What did the research involve?

The research used The Health Improvement Network (THIN), a large computer database of anonymous medical records that have been routinely collected from general practices since 1987. The database holds information on all medical diagnoses and prescriptions, sociodemographics, hospital referrals and clinic letters. In 2005, researchers examined the prevalence of COPD, looking at data on 1,025,662 people over the age of 35 for whom data on height were available (85% of the total database population eligible).

The researchers calculated the odds of a person being diagnosed with COPD depending on their height. The results were analysed separately by age, sex and adult sociodemographic status.

What were the basic results?

Of the eligible population aged over 35 years, 2.7% had a diagnosis of COPD. Being male significantly increased the risk of having COPD, as did increasing age and increasing social deprivation. Risk of COPD was also found to be associated with height, with greater height associated with a reduced risk of COPD. Compared to the shortest 20% of participants, the tallest 20% of participants were 39% less likely to have COPD (odds ratio 0.61, 95% CI 0.58 to 0.63).

These results took into account (were adjusted for) the participants’ age, sex and social deprivation. When adjusting for age, the researchers found that the association with height was greatest in the youngest age groups. Being shorter seemed to have greater impact on a person’s risk of COPD if they were aged 35 to 49 years, but had progressively less effect with each increase in age category.

After adjusting for sex, age group and social deprivation score, the average height difference between people with and without COPD was 1.12cm.

How did the researchers interpret the results?

The researchers concluded that the risk of developing COPD is strongly associated with adult height. They said this association was strongest in the youngest age category, and this suggests “that early life experience will remain an important risk factor for COPD for some time to come and possibly that COPD related to early life deprivation is more severe and tends to be present at a younger age”.

Conclusion

This cross-sectional study of over a million people found an association between shorter height and the likelihood of having COPD. The researchers do not suggest that short stature causes COPD, but that it is a marker of social deprivation in childhood, which is historically linked with an increased risk of developing disease in adulthood. This study cannot provide any information on the cause of COPD.

Although this study used data from over a million people, and made some effort to take into account some possible confounding factors, such as age and social deprivation, it did not take into account smoking, which is the most important risk factor for COPD. If the researchers had taken this into account, then it would have been possible to see whether other aspects of social deprivation such as poor diet and environment are associated with COPD, as well as smoking.

An additional limitation, as the researchers acknowledge, is that there may have been miscoding of some of the COPD diagnoses or heights in the database.