Risk factors for COPD spirometrically defined from the lower limit of normal in the BOLD project

Chronic obstructive pulmonary disease (COPD) is predicted to become the third most common cause of death and disability worldwide by 2020. The prevalence of COPD defined by the lower limit of normal was estimated using high-quality spirometry in surveys of 14 populations aged >= 40 yrs. The strength and consistency of associations were assessed using random effects meta-analysis. Pack-years of smoking were associated with risk of COPD at each site. After adjusting for this effect, we still observed significant associations of COPD risk with age (OR 1.52 for a 10 yr age difference, 95% Cl 1.35-1.71), body mass index in obese compared with normal weight (OR 0.50, 95% Cl 0.37-0.67), level of education completed (OR 0.76, 95% Cl 0.67-0.87), hospitalisation with a respiratory problem before age 10 yrs (OR 2.35, 95% Cl 1.42-3.91), passive cigarette smoke exposure (OR 1.24, 95% Cl 1.05-1.47), tuberculosis (OR 1.78, 95% Cl 1.17-2.72) and a family history of COPD (OR 1.50, 95% Cl 1.19-1.90). Although smoking is the most important risk factor for COPD, other risk factors are also important. More research is required to elucidate relevant risk factors in low- and middle-income countries where the greatest impact of COPD will occur.