Antioxidants and air pollution in relation to indicators of asthma and COPD

Abstract

Two main research questions were specified in this thesis. First, whether acute respiratory effects of air pollution can be modulated by antioxidants. Second, whether dietary or plasma antioxidants were associated with indicators of asthma and COPD.Two intervention studies investigated a possible modulation of the acute respiratory effects of ozone by antioxidant supplementation. In addition a panel study examined a possible modulation of the acute respiratory effects of winter air pollution by antioxidants in diet and serum.The first intervention study in 1994 was a pilot study among 26 cyclists who performed lung function measurements (192 observations) before and after exercise. Half of the group was randomly assigned to the supplementation group and were given a daily antioxidant supplementation of vitamins C, E andβ-carotene. The control group did not receive a placebo. We repeated the study in the summer of 1996 with a similar design but this time the study was placebo-controlled. In this study, 38 subjects (380 lung function measurements) participated until the end of the study and the antioxidant supplementation consisted of a cocktail of vitamins C and E.Both intervention studies suggest that there was an effect of ozone on FEV 1 and FVC in the control group. There was no change in lung function when ozone levels were high in the supplementation group. The difference in ozone effect between the groups for both studies was statistically significant for FEV 1 and FVC. In the analysis of the panel study, we included only subjects with chronic respiratory symptoms because these subjects showed clear acute respiratory effects of air pollution. The results suggest that subjects with low levels of plasmaβ-carotene showed an effect of air pollution on large PEF decrements, in particular, for PM10 and black smoke, whereas subjects with high levels of plasmaβ-carotene did not show an effect of air pollution. No difference in acute respiratory effects of air pollution was observed for a high versus a low dietary intake of vitamin C, E andβ-carotene or for plasmaα-tocopherol.The second research question was investigated within the MORGEN study. This study is a cross-sectional investigation on the prevalence of risk factors for chronic diseases using self-administered questionnaires and a physical examination in a randomly selected sample of the Dutch population.First, we examined the relations between dietary antioxidants (vitamins C, E andβ-carotene) and the prevalence of a number of respiratory symptoms and lung function in a population based sample of 6,555 adults. Our results suggested that a high dietary vitamin C andβ-carotene intake was associated with a higher FEV 1 and FVC. Dietary vitamin E was not associated with lung function. None of the dietary antioxidants were consistently associated with the prevalence of a number of respiratory symptoms.Second, we studied the relation between plasma levels ofβ-carotene orα-tocopherol and respiratory symptoms in a case-control sample of never and long-term former smokers. Our results suggested that cases (subjects with one or more chronic respiratory symptoms; n=491) tended to have lower plasmaβ-carotene levels than controls (n=496). Plasmaα-tocopherol was not associated with asthma and chronic bronchitis symptoms but was positively associated with dyspnea. This adverse association of plasmaα-tocopherol could not be explained by adjustment for cardiovascular risk factors and remains puzzling. Third, we evaluated the relation between plasma antioxidants (β-carotene andα-tocopherol) and lung function in a random sample (n=367) of the MORGEN study. We found that subjects with a high plasmaβ-carotene concentration tended to have a higher FVC and FEV 1 than subjects with a low plasmaβ-carotene concentration but this was not statistically significant for FEV 1 . Plasmaα-tocopherol was not associated with lung function.</p