Does dietary vitamin A protect against airway obstruction?

A recent report based on data from the first National Health and Nutrition Examination Survey suggested that low intake of vitamin A may be associated with a greater risk of airway obstruction. We attempted to replicate these findings in a population-based sample of middle-aged adults (n = 15,743) who participated in the baseline examination of the Atherosclerosis Risk in Communities (ARIC) Study. Vitamin A intake was estimated from a 66-item food frequency questionnaire, and the presence of airway obstruction was determined by spirometry. Although airway obstruction was associated in ARIC with well-established risk factors such as age, sex, and smoking, there was little evidence for a role of vitamin A. With only one exception, vitamin A intake was unrelated to airway obstruction in all smoking categories using either categorical or continuous measures of lung function (FEV₁, FVC, FEV₁/FVC). Only among current smokers in the upper tertile of lifetime cigarette smoking (> 41 pack-years) was the odds ratio of having airway obstruction for the lowest quartile of vitamin A intake compared with the highest quartile elevated (1.7 [95% confidence interval 1.1 to 2.7]). Despite some biological plausibility that vitamin A intake may prevent obstructive lung disease, the inability to demonstrate association in a larger population study, with better estimation of usual dietary intake, casts doubt on the existence of causal relationship.