Author: Andre F.S. Amaral

Cough! Cough! Cough!

Chronic cough is a common respiratory symptom that affects the life of millions of people

Coughing on most days, without having a cold, for several months is one of the most common reasons why people book an appointment with their GP. Chronic cough is bothersome and has been linked to poorer health in people without obvious disease. However, the prevalence of – that is the proportion of people with – chronic cough and its associated risk factors are not well known in different regions of the world.

Using data from adults in the multinational Burden of Obstructive Lung Disease (BOLD) study, we estimated the prevalence of chronic cough in 41 locations from 34 countries around the globe and identified the factors that are more likely to determine the occurrence of chronic cough. We found a wide variation in the proportion of people with chronic cough across the different study locations – from 3% in Pune (India) to 24% in Lexington, KY (United States of America). Perhaps not surprisingly, tobacco smoking and working in a dusty job were the main risk factors for chronic cough. We identified other factors such as passive smoking, having had tuberculosis, being obese, having a low level of education and having hypertension.

Chronic cough population attributable risk for several factors across 41 sites of the BOLD study.


Despite our findings, in many locations, we still cannot explain all of the prevalence of this chronic cough.

This manuscript has been published in eClinicalMedicine and is available here: This work was conducted as part of the PhD thesis of Hazim Abozid.

The Burden of Obstructive Lung Disease cohort

The BOLD study’s past and present

The Burden of Obstructive Lung Disease (BOLD) cohort is a large, multinational, prospective study of chronic respiraWorld map showing sites where the large multinational prospective BOLD study was conducted.tory disease. It started with the intention to measure the prevalence, risk factors, and impact of chronic obstructive pulmonary disease (COPD) in different populations around the world. COPD is a common and serious lung condition that causes breathing difficulties, coughing, wheezing, and reduced quality of life. It is estimated that COPD affects around 300 million people worldwide and is a leading cause of death globally.

The BOLD study has been a reference in the study of COPD because of its strengths:

• wide coverage of world regions and ethnic groups;

• large sample of representative population-based data;

• use of a standardised protocol, including the same questionnaires and same model of machine to test lung function, across study sites;

• centralised training and certification of interviewers and spirometry technicians. The quality of the data was monitored throughout the study, and re-training of staff was carried out if necessary;

• high quality of lung function measurements made before and after administration of a bronchodilator, with centralized quality control and assessment of all spirometry curves.

The BOLD cohort is still ongoing and will continue to provide important data and insights for the prevention, diagnosis, and management of COPD. More details about the past and present BOLD cohort can be found on the study’s website and in the profile published in the International Journal of Epidemiology (

Lung disease and exposures in occupational settings

Respiratory symptoms are common among dust- and fume-exposed workers

It has been suggested that about 15 in 100 cases of chronic lung disease are caused by workplace exposures. These exposures can be anything from noxious gases, dust, which are very small dry airborne particles of biological or mineral origin, and fumes, such as those generated from welding. Most of the evidence that supports this estimate comes from wealthy countries in Europe and North America. Data on the association of lung disease with occupational exposures in other regions of the world are limited.

To improve the understanding of the relationship between occupational exposures and lung disease across the world, we used data from almost 29,000 adults, aged 40 and above, who participated in the Burden of Obstructive Lung Disease (BOLD) study. In this study, we asked participants about their job. We asked whether they worked in any of 11 settings considered to increase their exposure to dust or fumes. We also asked them whether they had a frequent cough, recurring mucous production, shortness of breath or wheezing. In addition, each of them had their lung function measured through spirometry.

We found that respiratory symptoms, that is frequent cough, recurring mucous production, shortness of breath and wheezing, were more common among people who worked in settings considered to have higher exposure to dusts and fumes. These findings were consistent across the several world regions. Interestingly and contrary to previous reports, we saw no evidence of a link between occupational exposures and worse lung function. At any rate, actions to avoid or reduce occupational exposures are still advised.

To learn more about this study check out the open-access peer-reviewed article in the European Respiratory Journal ( This work was conducted as part of the PhD thesis of Jate Ratanachina.

Restricted lung function and cardiometabolic diseases

People with restrictive lung function are likely to also have heart disease or diabetes


Take a deep breath in and as you inhale, pay attention to your lungs and chest expanding. Now, imagine you could not expand your lungs to their maximum capacity. The inability to fully expand the lungs when inhaling is usually a sign of restrictive lung function. This condition has been linked to worse quality of life, increased mortality, and it is a good predictor of reduced life expectancy even among people who have never smoked in their life.

Using data from almost 24,000 people, aged 40 years and above, who participated in the multinational Burden of Obstructive Lung Disease (BOLD) study, we have investigated the relationship between restrictive lung function and hypertension, cardiovascular disease, and diabetes. Participants in this study provided information on several aspects of their life, including whether they had been diagnosed with specific diseases, whether they smoke or smoked, their weight, and their highest level of education. Lung function was measured through spirometry.

Almost a third of the participants in the BOLD study had restrictive lung function. Most of these people live in Africa and Asia. One in 4 participants had hypertension, 1 in 10 had cardiovascular disease and 8 in 100 had diabetes. The odds of having hypertension or cardiovascular disease were 50% higher among people with restrictive lung function than among people without this lung condition. The odds of having diabetes were 86% higher. These findings were independent of age, sex, level of education, whether they smoked, and whether they were underweight or obese.

The underlying reasons for the occurrence of restrictive lung function with hypertension, cardiovascular disease and diabetes are not known. Therefore, there is a need for more studies to investigate this relationship.

The findings of this study were published in the peer-reviewed journal Respiratory Research. The article can be read here: