Is Vitamin C Good for Asthma and Wheezing?
Last updated: January 23, 2019
Some studies suggest vitamin C might help control wheezing and other symptoms in people with certain types of asthma. These beneficial effects might be linked to the antioxidant and anti-inflammatory properties of vitamin C.
In this article, we look at epidemiological studies and clinical trials that have been done on vitamin C and asthma.
Epidemiological Studies
Several epidemiological studies have examined whether a high intake of vitamin C is associated with a reduced risk of asthma. In a systematic review published in the journal Thorax, a group of researchers analyzed existing studies on the relationship between vitamin C intake and asthma, and found that low dietary intakes of vitamin C were associated with increased odds of asthma and wheeze.
However, another review, published just one year earlier in the journal Respirology, found no evidence of an inverse association between the intake of vitamin C and asthma risk per se—but it did find an association between increased intake of vitamin C and an increase in FEV1.
FEV1, which stands for Forced Expiratory Volume in 1 Second, is the maximum volume of air that can be exhaled in one second, and it is commonly used to measure lung function.
Clinical Trials
While epidemiological studies can detect associations, they cannot establish clear cause-and-effect relationships. Therefore, in order to better understand whether vitamin C can help protect against asthma and respiratory symptoms such as wheezing, we also have to look at randomized clinical trials, which are commonly considered the gold standard in evidence-based medicine.
Vitamin C and asthma induced by exercise
In one review, published in the journal Allergy, Asthma & Clinical Immunology in 2014, Harri Hemila, MD, PhD, of the University of Helsinki, Finland, analyzed the results of nine clinical trials exploring the effects of vitamin C on bronchoconstriction (constriction of the airways in the lungs) and respiratory symptoms caused by exercise, with promising results.
A meta-analysis of three clinical trials included in his review found that vitamin C reduced the decline in post-exercise FEV1 by 48 percent. Five other clinical trials included in Dr. Hemila's review examined people who were under short-term, heavy physical stress, and vitamin C was found to reduce the incidence of respiratory symptoms in this group of people by 52 percent. Yet another clinical trial found that vitamin C halved the duration of the respiratory symptoms in young competitive swimmers.
In another review, published in the Cochrane Database of Systematic Reviews in 2013, Dr. Stephen Milan of Lancaster University and his co-authors noted that while there was some evidence of improved lung function with vitamin C supplementation in people with exercise-induced bronchoconstriction, the clinical trials exploring the topic were few and small, and offered limited data. Therefore, more research is needed before any firm conclusions can be made about the effects of vitamin C on respiratory symptoms caused by exercise.
In addition to looking at the effects of vitamin C on exercice-induced bronchoconstriction, Dr. Milan's team also analyzed the results of randomized clinical trials focused on the potential of vitamin C supplements to prevent asthma exacerbations in general and to improve Health-Related Quality of Life (HRQL) in asthmatics. Unfortunately, however, the researchers did not find clear indication of benefit from the clinical trials that were included in their meta-analysis.
They did point out, however, that the findings were inconclusive as there was not enough high-quality data available. The researchers concluded that there is currently insufficient evidence to evaluate the use of vitamin C as a treatment for asthma in general.
It is also important to note that the short-term use of vitamin C supplementation at the time of exacerbations or for cold symptoms in people with asthma were outside of the scope of this review.
Vitamin C for Common Cold-Induced Asthma
In yet another systematic review, Dr. Hemila investigated whether vitamin C supplementation could have a protective effect against common cold-induced asthma.
Colds and the flu are among the most common triggers of asthma attacks, and finding a way to treat asthma triggered or exacerbated by these common illnesses could bring relief to the millions of adults and children who suffer from asthma.
For this study, which appeared in the journal Allergy, Asthma and Clinical Immunology, Dr. Hemila identified three previous intervention studies that were relevant for examining the effect of vitamin C on common cold-induced asthma. The three studies had a total of 79 participants, and two of the studies were randomized double-blind placebo-controlled trials. The third study did not use a placebo.
All three studies found that vitamin C supplementation had a protective effect, either against asthma attacks or against bronchial hypersensitivity which is a characteristic of asthma.
Given the findings of this systematic review, and the evidence that vitamin C may help prevent or alleviate colds, Dr. Hemila stated that asthmatics might want to test vitamin C on an individual basis if their condition is exacerbated by respiratory infections. He added, however, that more research on the effects of vitamin C on common cold-induced asthma is needed.
Conclusion
To sum, low intakes of vitamin C have been associated with increased odds of asthma and/or a decline in lung function in several observational studies, but the results of clinical studies have been less conclusive.
However, the current evidence points to the possibility that supplemental vitamin C might be beneficial for people with certain types of asthma only. In fact, Dr. Harri Hemila who has conducted extensive research on the topic, explained in a letter to the Editor of The Journal of Allergy and Clinical Immunology that "mitochondrial respiration and inflammatory cells are an endogenous source of oxidative stress". Therefore, he added, "the pulmonary effects of vitamin C might be most pronounced when a person exercises or suffers from infections".
The idea that different types (and subtypes) of asthma may respond differently to various nutritional treatments has also resonated with other researchers and authors. Indeed, in an article that appeared in the Expert Review of Respiratory Medicine in 2016, the authors Raphaelle Varraso and Carlos Camargo concluded that better asthma phenotyping is necessary in order for scientists to really understand how dietary factors might affect asthma.
Recommended Guide
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