Systemic inflammation has been associated with reduced lung function. However, data on the interrelationships between lung function and inflammation are sparse, and it is not clear if low-grade inflammation leads to reduced lung function.Associations between high-sensitive C-reactive protein (CRP) and spirometric lung function were assessed in a population-based cohort of ,1,000 Danes aged 20 yrs.In males, the average decline in forced expiratory volume in one second (FEV1) in the highest CRP quintile was 23 mL?yr -1 versus 1.6 mL?yr -1 in the lowest quintile. In females, the average decline was 6.2 mL?yr -1 in the highest CRP quintile versus an increase of 1.8 mL?yr -1 in the lowest CRP quintile. In a multiple regression analysis adjusted for sex, body mass index, cardiorespiratory fitness, smoking, asthma, airway hyperresponsiveness and serum eosinophil cationic protein, higher levels of CRP at age 20 yrs were associated with a greater reduction in both FEV1 and forced vital capacity between ages 20 and 29 yrs. The findings show that higher levels of C-reactive protein in young adults are associated with subsequent decline in lung function, suggesting that low-grade systemic inflammation in young adulthood may lead to impaired lung function independently of the effects of smoking, obesity, cardiorespiratory fitness, asthma and eosinophilic inflammation.

This finding provide further evidence of a possible beneficial effect of physical activity in childhood on the development of respiratory symptoms in adulthood and supports the notion that the lower levels of physical activity in recent decades may have contributed to an increase in the prevalence of asthma and asthma-like symptoms.