Body Mass Index and Lung Function in the General Population: A Systematic Review and Meta-analysis with Occupational Health Implications

Abstract

Background Across the globe obesity rates continue to rise. With this trend comes related concerns for health consequences associated with obesity. Thus, there is a need for greater data and understanding on this topic. While there can be a host of impacts to health related to adiposity, of particular interest is how excess weight affects lung function in adults without diagnosed respiratory disease. Spirometry is widely used in occupational health to monitor respiratory trends, yet interpretation can be complicated by individual characteristics such as body mass index (BMI), which may independently influence lung volumes. However, evidence in healthy adults remains inconsistent, and few syntheses have examined this relationship with a focus on both sexes or considered the implications for occupational health. Objective This meta-analysis aimed to systematically review and synthesise evidence on the relationship between BMI and spirometry-based lung function outcomes, specifically forced expiratory volume in one second (FEV1) and forced vital capacity (FVC), in adults from the general population. Secondly, it considered the potential implications for occupational health surveillance. Methods A structured search of Ovid MEDLINE was conducted for studies published from 2005 to 2025. Inclusion criteria were studies that reported FEV1 or FVC per unit increase in BMI in adults aged 19 years or older. Exclusion criteria were studies based solely on clinical populations or those lacking sufficient data for analysis were excluded. Random effects models were used to pool effect estimates separately for males and females. Study quality was assessed using the Newcastle Ottawa Scale. Results The initial search retrieved 600 records, of which four population-based studies met the inclusion criteria for the meta-analysis. Pooled mean differences in FEV1 and FVC per unit increase in BMI were not statistically significant for either sex. In males, each unit increase in BMI was associated with −17.12 mL (95% CI: −40.85, 6.61) for FEV1 and −38.36 mL (95% CI: −77.83, 1.11) for FVC. In females, the changes were −8.02 mL (95% CI: −21.13, 5.10) for FEV1 and −6.44 mL (95% CI: −19.33, 6.45) for FVC. Results varied widely across studies, and substantial heterogeneity was present in all models. Some studies found higher BMI was linked to lower lung function, particularly in men, while others found no association or modest increases among women. These inconsistencies reflect differences in study methodology, population characteristics, and the limitations of BMI as a measure of adiposity. Conclusion Although the overall findings did not confirm a consistent association between BMI and lung function, the variability suggests that body weight may influence respiratory outcomes in complex ways. The results indicate that excess weight could contribute to reduced FEV1 and FVC through mechanical pathways. In occupational health settings, accounting for individual differences in BMI and fat distribution may improve the interpretation of spirometry results and support earlier identification of risk. Future research should incorporate more precise measures of body composition and follow participants over time to gather more accurate data and better understand these relationships.