Abstract
Objective: To investigate the effect of vitamin C supplementation in decreasing asthma severity, medications, and improving pulmonary function tests (PFTs).
Methodology: Search of electronic databases was conducted to identify relevant studies published from January 2010 up to November 2023. A total of 105 records were initially identified. After filtering and screening, just 9 studies met the inclusion criteria; 3 were reviews, while the remaining 6 were original. Of the original studies, one was experimental, performed on 24 male Balb/c mice while the remaining 5 were performed on 969 asthmatic patients. Except for the experimental study, the selected studies were performed in different settings and on different ethnicities at the age of seven years and over.
Results: The results showed antioxidant effects of vitamin C in asthmatic patients and experimental models. The studies showed that vitamin-C supplements significantly contributed to the reduction in asthma severity, number of attacks, admission rate, and asthma medications. Also, improvement of PFTs and suppression of asthma phenotype features in asthma mouse models. Only one review showed non-significant improvement in symptoms and PFTs, with significant improvement in malondialdehyde level and superoxide dismutase activity.
Conclusion: Vitamin C supplementation to asthmatic patients showed improvements in asthma symptoms and PFTs, decreases the dose of asthma medications through potentiation of their efficacy, and less reactive response in asthma mouse model.

Key words: Vitamin C, asthma, antioxidant, oxidative stress, respiratory function.