Table 1

Trials on vitamin C supplementation and exercise-induced bronchoconstriction

Schachter and Schlesinger20MethodsRandomised, double-blind, placebo-controlled crossover trial
Participants12 asthmatic participants, selected from among workers of Yale University in the USA: “all 12 participants gave a characteristic description of EIB.” All included participants had at least 20% reduction in maximal expiratory flow 40% after exercise
5 Males, 7 females; mean age of 26 years (SD 5 years)
Type of exerciseExercise by using a cycloergometer was begun at a constant speed of 20 km/h against a zero workload. At the end of each 1 min interval, the workload was increased by 150 kpm/min, keeping the pedalling speed constant throughout the experiment. Exercise against progressively larger workloads was continued until either the heart rate reached 170 bpm or the participants fatigued
InterventionOn 2 subsequent days, the participants ingested 0.5 g of vitamin C or sucrose placebo in identical capsules 1.5 h before the exercise. Washout overnight
OutcomeChange in FEV1 was calculated as: (preexercise vs 5 min postexercise)
NotesSee online supplementary file 2 for the calculation of the vitamin C effect from the individual-level data
Cohen et al21MethodsRandomised, double-blind, placebo-controlled crossover trial
Participants20 asthmatic participants in Israel. All of them had demonstrated EIB by having a ‘decline of at least 15%’ in FEV1 after a standard exercise test
13 Males, 7 females; mean age of 14 years (range 7–28 years)
Type of exerciseA 7 min exercise session using a motorised treadmill. Each participant exercised to submaximal effort at a speed and slope to provide 80% of the motional oxygen consumption as adjudged by a pulse oximeter
Intervention2 g of vitamin C or placebo 1 h before the exercise. Washout 1 week
OutcomesChange in FEV1 was calculated as: (preexercise vs 8 min postexercise). Secondary outcome: proportion of participants who suffered from EIB after the exercise session (decline in FEV1 at least 15%)
NotesIndividual-level data on the FEV1 levels was reported only for 11 of the 20 participants (Cohen et al, table 2). Dr Cohen was contacted, but he no longer had the data. Therefore, a conservative ‘no vitamin C effect’ was imputed for the 9 participants for whom experimental data were not available; see online supplementary file 2
Tecklenburg et al11MethodsRandomised, double-blind, placebo-controlled crossover trial
Participants8 participants from a population of university students and the local community, Indiana, USA, with physician-diagnosed mild-to-moderate asthma. All participants had documented EIB as indicated by a ‘drop greater than 10%’ in postexercise FEV1. They also had a history of chest tightness, shortness of breath and intermittent wheezing following exercise.
2 Males, 6 females; mean age of 24.5 years (SD 5 years)
Type of exerciseParticipants ran on a motorised treadmill, elevated by 1% per min until 85% of the age-predicted maximum heart rate and ventilation exceeding 40–60% of the predicted maximum voluntary ventilation. Participants maintained this exercise intensity for 6 min. Following the 6 min steady state exercise, the grade of the treadmill continued to increase at 1% per min until volitional exhaustion
Intervention1.5 g vitamin C or sucrose placebo was administered as capsules matched for colour and size daily for 2 weeks. Washout 1 week.
Participants were advised to avoid high vitamin C foods during the study
OutcomeChange in FEV1 was calculated as: (preexercise vs the lowest value within 30 min postexercise)
NotesDr Tecklenburg kindly made the mean and SD for the paired FEV1 decline available. For the decline in FEV1 level, the mean difference was +6.5 percentage points (paired SD 7.4) in favour or vitamin C
  • EIB, exercise-induced bronchoconstriction; FEV1, forced expiratory volume in 1 s.