Gender difference in the association between smoking and lung function: exploring the role of C-reactive protein as a mediating factor

Objectives: Exposure to smoking causes inflammatory damage to the airways, and in turn declines lung function. Meanwhile gender difference in the association between smoking and lung function has been reported. This study aimed to assess the extent to which C-reactive protein (CRP) mediates the association of smoking with lung function and explains gender difference in this association.

Study design: The study design is a cross-sectional study.

Methods: Data were taken from the English Longitudinal Study of Aging, Wave 6 (2012-2013). Lung function parameters including forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) were measured by using a spirometer. Smoking status was self-reported by questionnaires. CRP was analyzed from peripheral blood. Multiple linear regression models stratified by gender were fitted to assess the gender difference. Karlson/Holm/Bree method was used to test the mediating effect.

Results: Of all people, 11.8% of men and 11.2% of women reported current smoking. The association between smoking and lung function was greater in men than in women (P-interaction<0.001 for FEV1; P-interaction = 0.028 for FVC). Women had a higher CRP (P = 0.006), but a weaker association between CRP and lung function (P-interaction<0.001 for FEV1; P-interaction<0.001 for FVC). The indirect effects of current smoking on lung function via CRP were significant in both men and women, with 7.76%-19.40% of the total effect being mediated.

Conclusions: CRP mediates the association between smoking and lung function. The gender difference in the risk effect of smoking on lung function might be partially explained by the different susceptibility to inflammatory process in men and women.