DOES DIETARY VITAMIN-A PROTECT AGAINST AIRWAY-OBSTRUCTION

A recent report based on data from the first National Health and Nutri tion Examination Survey suggested that tow 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 a dults (n = 15,743) who participated in the baseline examination of the Atherosclerosis Risk in Communities (ARIC) Study. Vitamin A intake wa s estimated from a 66-item food frequency questionnaire, and the prese nce of airway obstruction was determined by spirometry. Although airwa y obstruction was associated in ARIC with well-established risk factor s 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 categoric al or continuous measures of lung function (FEV(1), FVC, FEV(1)/FVC). Only among current smokers in the upper tertile of lifetime cigarette smoking (> 41 pack-years) was the odds ratio of having airway obstruct ion for the lowest quartile of vitamin A intake compared with the high est quartile elevated (1.7 [95% confidence interval 1.1 to 2.7]). Desp ite some biological plausibility that vitamin A intake may prevent obs tructive lung disease, the inability to demonstrate association in a l arger population study, with better estimation of usual dietary intake , casts doubt on the existence of causal relationship