The effects of antioxidant vitamin supplementation on expiratory flow rates at rest and during exercise

Purpose: Previous studies suggest that pulmonary function is associated with fruit and vegetable consumption and plasma concentrations of antioxidant vitamins. Also, expiratory flow limitation (EFL) has been reported to limit ventilation during exercise in healthy individuals. We hypothesized antioxidant vitamin supplementation (AVS) would increase resting expiratory flow rates in healthy subjects and reduce EFL during exercise. Methods: Ten healthy, nonsmoking subjects (5 M/5 W), consuming <5 servings of fruit and vegetables per day, participated in a randomized, single-blinded crossover design study with subjects receiving a placebo (PLA) or AVS [vitamins C (500 mg), E (400 IU), beta-carotene (15,000 IU), zinc (7.5 mg), selenium (50 mg), copper (1 mg), and manganese (2.5 mg)] for 4 weeks. After a minimum 4-week washout period, subjects received the alternate supplementation. Pulmonary function tests and total antioxidant status (TAS) from plasma were measured pre- and post-supplement period. Subjects completed a pre- and post-supplement treadmill test for 20 min at 70 % $$\dot V \text{O}_{2\text {max}}$$V˙O2max followed by increasing workload until exhaustion. Results: AVS increased (p < 0.05) TAS by ~21 % and resting expiratory flow rates (FEF_25–75, FEF₅₀) by ~9 %. Following AVS, %EFL was significantly reduced by ~15 % at minute 15, 20, and end-exercise with no change (p > 0.05) in end-expiratory lung volumes. Breathing frequency and ratings of perceived exertion and dyspnea were also lower (p < 0.05) at min 20 of exercise. No changes (p > 0.05) were evident at rest or during exercise with PLA. Conclusions: These results suggest that AVS can increase TAS, improve resting expiratory flow rates and reduce EFL during exercise in healthy subjects who are not meeting fruit and vegetable recommendations.