Lung function declines more rapidly in individuals who experience moderate or high weight gain, according to a study led by the Barcelona Institute for Global Health (ISGlobal), which analysed the effect of weight changes on respiratory health over a 20-year period.
The study, 'Body mass index and weight change are associated with adult lung function trajectories: the prospective ECRHS study', published in the journal Thorax, was based on data collected from 3,700 participants living in different countries in Europe and in Australia and recruited between the ages of 20 and 44 years. Participants repeatedly underwent measurements of weight and lung function - by means of spirometry - between 1991 and 2014.
"Although previous research has shown that weight gain is linked to lung function decline, ours is the first study to analyse such a varied population sample over a longer period of time," explained Judith Garcia Aymerich, leader of the study and head of the Non-communicable Diseases and Environment program at ISGlobal. Most earlier studies have had relatively short follow-up periods, ten years at the most, and focused on adults up to 50 years of age.
Information on other potentially influential factors was also collected: whether they smoked or had been exposed to secondhand smoke; whether they had asthma; how often they exercised; and whether they had any other serious condition, such as diabetes or cancer.
Their average age was 34 at the start of the study, and 54 when they had their last check-up. At the start of the study, around one in eight (12%) was underweight; over half (57%) were of normal weight; around one in four (24%) was overweight; around one in 20 (6%) was obese.
During the monitoring period, almost 4% of participants lost weight, while weight didn't change in around a third (34%). Around half (53%) put on a moderate amount of weight (0.25-1 kg/year), and around one in 10 (9%) put on a lot of weight (more than 1 kg/year).
The study found that people with a BMI within the recommended rates, overweight people and people with obesity all experienced accelerated lung function decline when they gained weight. Conversely, weight loss helped to attenuate lung function decline in obese people. Moreover, people who kept their weight low throughout adulthood exhibited a much less pronounced decline in respiratory health.
Two mechanisms could explain the association between weight gain and pulmonary health. First, weight gain can affect lung function through mechanical effects.
"Abdominal and thoracic fat mass is likely to limit the room for lung expansion during inspiration," added ISGlobal researcher Gabriela Prado Peralta, lead author of the study. Second, weight gain can impair lung function through inflammatory processes, since adipose tissue (the area where fat accumulates) is a source of inflammatory substances that can damage lung tissue and reduce airway diameter.
Maintaining good lung function during adulthood is crucial to prevent chronic respiratory diseases, which nowadays represent a serious public health problem around the world.
"Given the epidemic levels of overweight and obesity that we are currently seeing, it is fundamental to understand the effects of weight changes on lung function, which is a powerful predictor of morbidity and mortality in the general population," said Garcia Aymerich. "The good news is that the negative pulmonary health effects of excess weight and obesity can be reversed through weight loss. Therefore, public health policies that promote healthy lifestyles can be the key to achieving good pulmonary health."
The study formed part of the Ageing Lungs in European Cohorts (ALEC) Study, coordinated by Imperial College London. It was financed by the European Union's Horizon 2020 research and innovation program.