In our preclinical study, we have demonstrated that 4 fold increase in plasma quercetin levels significantly decreased lung inflammation and prevented progression. Clinical studies in healthy volunteers 4 fold increase in plasma quercetin levels (0.22 to 1 µM) could be achieved by supplementing with 500mg of quercetin/day. However, safety of quercetin supplementation and quercetin dose required to achieve 4 fold increases in plasma quercetin levels in 'at-high-risk' COPD population is yet to be established. This study involves two phases; the first phase examines the safety of quercetin supplementation in subjects with chronic obstructive pulmonary disease (COPD) and the second phase determines the efficacy of quercetin in COPD patients. In this study, we will enroll COPD patients with mild to moderate disease between the age group of 40 to 65 years. During the first phase, we will enroll a total of 9 patients to examine the tolerance and safety of three doses of quercetin (500, 1000 and 2000 mg/day) in a dose escalation manner. First cohort consisting of three subjects will receive placebo or 500 mg of quercetin per day for one week and the safety of quercetin supplementation will be assessed by monitoring adverse events and any changes in outcomes of blood test that include complete blood counts (CBC)and comprehensive metabolic panel prior to after supplementation. If this dose is safe and tolerated, second cohort of 3 subjects will receive placebo or 1000 mg of quercetin per day quercetin for one week and again safety will be assessed. If the dose is safely tolerated, the third cohort will receive either placebo or 2000 mg of quercetin per day for a week and the safety will be assessed.