Lung function and plasma fibrinogen concentrations in the Newcastle Thousand Families birth cohort between age 49 and 51 years

Background and objectiveA number of studies have suggested inverse associations between lung function and inflammatory markers, including fibrinogen. In this study, we used data from the Newcastle Thousand Families birth cohort to assess the association between contemporaneous markers of lung function and fibrinogen while adjusting for potential confounding factors throughout life. MethodsAt age 49-51 years, complete data on lung function and plasma fibrinogen were available for 380 study members. These data were analysed in relation to each other, adjusted for sex and height, with further adjustment for potential confounders within linear regression models using robust estimates. ResultsForced expiratory volume in 1s was significantly inversely associated with plasma fibrinogen concentration after initial adjustments for sex and height (beta=-0.12, P=0.011) and remained so after further adjustments for pack-years of cigarettes smoked and current smoking status. On further adjustment for standardized birthweight and duration breast-fed, the association approached statistical significance (P=0.051). Adjusting for body mass index (BMI) resulted in a loss of significance (P=0.09), but an unchanged regression coefficient, while, after adjustment for percent body fat, rather than BMI, the association was no longer significant (P=0.20) and the coefficient reduced. ConclusionsThe association between lung function and fibrinogen remains after adjustment for potential early-life confounders and smoking. However, it is not independent of contemporaneous measures of adiposity, with evidence of confounding by percent body fat. Further studies, with measures of adiposity, are required to confirm whether associations between markers of inflammation and lung function are due to residual confounding by adiposity. While lung function is inversely associated with inflammation, questions arise as to whether this is due to confounding by factors such as smoking, adiposity or early growth. We found evidence of confounding by percentage body fat, which appears to be a stronger confounder than body mass index. See Editorial, page 3