Original Contribution
Vitamin supplementation does not protect against symptoms in ozone-responsive subjects

https://doi.org/10.1016/j.freeradbiomed.2005.10.050Get rights and content

Abstract

Vitamin supplements have been reported to reduce the magnitude of symptoms in subjects exposed to oxidant air pollution. To confirm whether supplementation with vitamins C and E could reduce lung function decrements, airway inflammation, and epithelial injury in subjects sensitive to ozone, a double-blinded, crossover control study was performed. Fourteen ozone-responsive subjects were randomly exposed to both air and ozone (0.2 ppm for 2 h) after 7 days of either placebo treatment or supplementation with vitamin C (500 mg/day) and E (100 mg/day). Lung function was assessed pre- and immediately postexposure and blood samples were taken at set intervals. Inflammatory, tissue injury, and antioxidant responses were examined in lavage fluid obtained by bronchoscopy 6 h postexposure. Exposure to ozone resulted in significant (P < 0.01) decrements in FEV1 with no protection observed following vitamin supplementation (−8.5%) versus placebo (−7.3%) treatment. Similarly, ozone-induced neutrophilia were of a similar magnitude after both treatments (P < 0.05). This lack of protection was observed despite elevated plasma vitamin C (+60.1%) and vitamin E (+51.4%) concentrations following supplementation, and increased vitamin C concentrations in the airways after supplementation following ozone exposure. These data do not therefore support the contention that acute ozone-induced symptoms can be attenuated through the use of dietary antioxidants in well-nourished individuals.

Introduction

A thin liquid layer, the respiratory tract lining fluid, has been shown to cover the surface of the respiratory epithelium from the nasal airways to the alveolar region [1]. This compartment therefore represents the first physical interface encountered by inhaled gases and particulates in the lung and hence the toxicity of these agents must be interpreted in the context of their initial reactions within this aqueous compartment. The pollutant gas ozone has been shown to be unable to diffuse across the RTLF to interact directly with the underlying epithelium due to its relative insolubility and high chemical reactivity with a broad spectrum of substrates present within this compartment. As its uptake into the RTLF is therefore coupled to its reaction with substrates at the air-gas interface its toxicity appears to be transmitted to the underlying epithelium by secondary oxidation products formed either by the direct ozonation of RTLF lipids or by the indirect action of other radical intermediates [2]. These species trigger the underlying cells to elaborate inflammatory signals [3] resulting in airway neutrophilia with ensuing tissue injury. It has been proposed that the formation of these cytotoxic species is opposed by a network of antioxidants within the RTLF: ascorbate [4], urate [5], reduced glutathione [6], α-tocopherol [7], extracellular superoxide dismutase [7], and glutathione peroxidase [8], as well as mucins in the conducting airways [9]. Thus the antioxidant composition of the RTLF has been proposed to represent a significant determinant of an individual's susceptibility to ozone [10].

Studies demonstrating that good lung function is associated with diets rich in antioxidants, i.e., fruits and vegetables [11], have been proposed to support this contention, though currently there are little data linking basal airway or blood antioxidant levels to individual responsiveness to oxidant gas exposures under controlled conditions [7], [12]. Despite this, the contention that boosting plasma antioxidant concentrations above the normal range might provide protection against oxidant pollutant gases such as ozone is widely held, based on the assumption that this will result in augmented RTLF antioxidant levels. Indeed, it has been demonstrated that increased intake of nutritional antioxidants reduces the magnitude of lung function decrements in subjects exposed to high ozone concentrations, both occupationally (shoe cleaners in Mexico City) [13] and recreationally (Dutch cyclists) [14], [15]. These findings have been collaborated in a number of controlled chamber studies [16], [17], [18]. The results of these chamber studies should, however, be interpreted with caution as they had limited group sizes and the subjects did not act as their own controls. Furthermore, although each chamber study revealed protection against ozone with vitamin supplementation, the endpoints for which protection was seen were not consistent, and the magnitude of protection small.

To test the hypothesis that antioxidant supplementation can protect against an environmentally relevant ozone challenge, we performed a randomised, double-blinded, crossover control study of the protective actions of vitamin C (500 mg) and E (100 mg) supplementation (7 days) in ozone-sensitive, but otherwise healthy subjects. Ozone-sensitive subjects were preselected, based on the magnitude of their bronchoconstriction response, and they were exposed on three separate occasions: once to air, and twice to ozone (0.2 ppm, for 2 h with moderate exercise) after vitamin supplementation and placebo treatment. Lung function was assessed pre- and immediately postexposure, when responses are maximal [19]. Airway inflammation was determined 6 h postchallenge, the period of maximal neutrophil influx into the lung after ozone [20]. A 7-day antioxidant supplementation period was chosen as this was known to significantly increase circulating concentrations of these antioxidants. This study therefore represents a fully controlled investigation of the protective action of vitamin C and E in sensitive human subjects acutely exposed to an environmentally relevant ozone concentration.

Section snippets

Subjects

All volunteers (26 females and 30 males, mean age 24 ± 3 years) prescreened for ozone-induced lung function responsiveness were healthy nonsmokers with normal lung function and no history of allergy, including negative skin prick tests and no preexisting lung disease. Subjects were recruited following a detailed medical examination and a full study briefing. Demographic details of the 15 “responder” subjects carried forward into the exposure-supplementation phase of the study are summarised in

Results

Following ozone exposure an overall decrease of 3.7 ± 6.1% in FEV1 was observed (P < 0.001), with a range of response from −27.0 to +6.9%. The 15 most responsive subjects (−11.3 ± 5.8%, range −27.0 to −6.1%) were selected and taken forward into the main study. The characteristics of these 15 subjects are summarised in Table 1. One subject withdrew from the study prior to the final exposure and the data from this subject are not included in the analysis. The remaining 14 subjects tolerated both

Discussion

Recent field studies in populations with high pollutant exposures have suggested that supplementation with antioxidants protects against O3-induced lung function decrements [13], [14], [15]. In support of these findings, a recent controlled exposure study reported a modest blunting of acute ozone-induced decrements in FEV1 in subjects presupplemented with a cocktail of antioxidants [17]. To further investigate the protective role of antioxidants against O3-induced symptoms (lung function

Acknowledgments

The authors acknowledge the valuable technical assistance of Helen Bertilsson, Sean Duggan, Annika Hagenbjörk-Gustafsson, Annika Johansson, Maj-Cari Ledin, Ann-Britt Lundström, and Helena Tjällgren.

The study was generously supported by the Swedish Heart and Lung Foundation, The Swedish Vårdal Foundation, Umeå University, Sweden, and the Food Standards Agency, UK (Contract No. 4019).

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