After adjustment for age, the statistically significant negative trend between serum Beclin1 protein level in each group persisted (non-smokers: 2.31 ± 0.23, smokers: 1.66 ± 0.23, and COPD: 1.52 ± 0.24 ng/mL, respectively; p = 0.036). This evidence concerns the gene BECN1 and chronic obstructive pulmonary disease.