Higher levels of systemic inflammation (IL-6 and CRP) in COPD than in smokers found in our study and in the Eclipse study [23] and lower intake of vitamin A in COPD compared to smokers (636.9 (339.6–1349.6) versus 918.0 (592.1–1654.6), P = 0.05) can explain why COPD patients and not smokers present decrease in serum vitamin A. There were other possible limitations to this study. Here, IL6 is linked to chronic obstructive pulmonary disease.