CRP and chronic obstructive pulmonary disease: 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.