The relation between vitamin A status and the degree of lung airway obstruction was examined in a cross-sectional study of 36 male subjects aged 43-74 y who were assigned to five groups as follows: healthy nonsmokers (n = 7), healthy smokers (n = 7), mild chronic obstructive pulmonary disease (COPD-mild) patients (n = 9), COPD-moderate-severe patients (n = 7), and COPD-moderate-severe patients with exacerbation (+ex; n = 6). Smoking habits, pulmonary function tests, and energy-protein status were assessed; serum concentrations of retinyl esters, retinol, retinol binding protein, and transthyretin and relative dose responses were measured. In addition, 12 male smokers aged 45-61 y with mild COPD were randomly assigned to two groups for a longitudinal study: six subjects consumed vitamin A (1000 RE/d; COPD- vitamin A) and six subjects received placebo for 30 d. Lowered serum retinol concentrations were found in the COPD-moderate-severe and COPD-moderate- severe+ex groups. Measurements of vitamin A status in healthy smokers and in COPD-mild patients were not different from those in healthy nonsmokers. The improvement of pulmonary function test results after vitamin A supplementation [mean increase for 1-s forced expiratory volume (FEV1) = 22.9% in the COPD-vitamin A group] may support the assumption of a local (respiratory) vitamin A deficiency in patients with this disease.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)