Abstract
Aim: Cross-sectional studies investigating the relationship between adiposity and respiratory function have given inconsistent results, especially in regard to spirometry. Few studies have used direct measures of body fat to explore this relationship. We investigated how body fat measured using bio-electrical impedance and Body Mass Index (BMI) as an indirect measure of adiposity, related to a range of respiratory function parameters and also how changes in these measures of adiposity affected respiratory function over 6 years follow-up.
Methods: Associations between percent body fat or BMI and spirometry, plethysmography, and diffusion capacity were analysed using multiple linear regression in non-smoking, non-asthmatic Study members from a population based birth cohort of approximately 1,000 men and women at age 32 years. Associations between changes in adiposity and respiratory function were explored using follow-up data at age 38 years.
Results: At age 32, higher percent body fat was associated with lower spirometric and plethysmographic lung volumes in both sexes but not with airflow obstruction or specific airway conductance. Similar trends were seen for body mass index (BMI). Neither measure was associated with diffusion capacity. Changes in percent body fat and BMI at follow-up were inversely associated with changes in spirometric and plethysmographic volumes. These changes were greater in men than women. There was no association with airflow obstruction or specific airway conductance in either sex. Diffusion capacity was also inversely associated with changes in adiposity, but this was due to a reduction in the alveolar volume.
Conclusion: Higher percent body fat is significantly associated with impairment in lung volumes. Overall there was little difference between percent body fat and BMI as measures of adiposity with respect to their influence on lung function. Increases in adiposity lead to reductions in lung volumes with apparently greater effects in men than women.