A case-control study of plasma antioxidant (pro-)vitamins in relation to respiratory symptoms in non-smokers.

The aim of this study was to investigate the relations between plasma levels of antioxidants, beta-carotene and alpha-tocopherol, and chronic respiratory symptoms in Dutch adults who never smoked or were long-term former smokers. Cases (who reported one or more respiratory symptoms) and controls were selected from a population-based cross-sectional study. Plasma concentrations of antioxidants were determined in 491 cases and 496 controls. ORs for the presence of chronic respiratory symptoms were estimated for quintiles of plasma antioxidant concentration after adjustment for age, gender, and body mass index. The OR of respiratory symptoms in all but the highest quintile of plasma beta-carotene decreased and were slightly below one. We saw no meaningful relation with plasma alpha-tocopherol.