Is Vitamin C an Effective Treatment for Asthma?
The potential health benefits of vitamin C are many and varied, and some (but not all) studies suggest that improved lung function might be one of them. In this article, we take a look at studies that have found a link between a high intake of vitamin C (or vitamin C supplementation) and certain types of asthma.
Effects of Vitamin C in People with Exercise-Induced Asthma
If you start wheezing or coughing during exercise, or if exercise makes it difficult for you to breathe, you may suffer from exercise-induced bronchoconstriction, or EIB. Exercise-induced broncho- constriction, which occurs when the airways of the lungs become narrow as a result of vigorous exercise, is common in people with asthma, with up to 90% of asthmatics suffering from the condition. By contrast, only about 10% of the non-asthmatic general population suffer from EIB. Due to the prevalence of EIB among asthmatics, EIB is considered a common symptom of asthma and is often referred to as exercise-induced asthma.
A strong antioxidant, vitamin C has been studied as a potential treatment for a wide variety of diseases and conditions, including exercise-induced asthma. An intriguing study published in the November 2014 issue of Allergy, Asthma & Clinical Immunology analyzed the results of nine previous studies on the potential protective effects of vitamin C in people with EIB, with promising results: all nine randomized trials suggest that vitamin C can have positive effects on pulmonary functions and respiratory symptoms in people engaging in heavy exercise. Vitamin C is involved in the metabolism of histamine, prostaglandins, and cysteinyl leukotrienes, all of which appear to play a role in the pathogenesis of EIB.
The study did caution, however, that there is still a lot we don't know about how vitamin C may help combat EIB/exercise-induced asthma and that further research is needed. But they also added that given the low cost and safety of vitamin C, and the consistency of positive findings in the nine studies on vitamin C against EIB and respiratory symptoms, it seems reasonable for physically active people with EIB or related respiratory symptoms to test whether vitamin C is beneficial on an individual basis.
Benefits for People with Common Cold-Induced Asthma
In another systematic review, Harri Hemila from the University of Helsinki in Finland studied whether vitamin C supplementation could have a protective effect against common cold-induced asthma. Colds and the flu are among the most common causes of asthma, and finding a way to treat asthma triggered or exacerbated by these common illnesses would certainly bring relief to the millions of adults and children who suffer from asthma.
Hemila identified three previous studies that were relevant for examining the role of vitamin C on common cold-induced asthma. The three studies had a total of 79 participants, and two of the studies were placebo-controlled. 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.
Vitamin C and Asthma in Children
Another study, carried out by scientists from the Tanta University in Egypt and the University of Helsinki in Finland, investigated the effects of vitamin C in 60 asthmatic children aged 7 to 10 years. During each 6-week study period, the children received a daily dose of either 0.2 grams of vitamin C or placebo.
The researchers found that the effect of vitamin C on the children's asthma symptoms depended largely on their age as well as exposure to molds or dampness in the bedroom. The benefit of vitamin C was greatest in the younger children aged 7.0 to 8.2 years with mild asthma symptoms and smallest in the older children aged 8.3 to 10 years with more severe asthma symptoms. To carry out this cross-over trial, the researchers used two methods that are commonly used to assess the severity of (childhood) asthma: the Childhood Asthma Control Test (C-ACT), which measures the severity of asthma symptoms on a scale from 0 to 27, and Forced Expiratory Volume in 1 second, also known as FEV1.
In yet another study, a team of Italian scientists examined whether fruit rich in vitamin could reduce wheezing and other respiratory symptoms in Italian children. Questionnaires were filled in by parents of 18,737 Italian children aged 6-7 years, and the winter intake of citrus fruit and kiwi fruit by each child was categorized as less than once per week, 1-2 per week, 3-4 per week, or 5-7 per week. As you probably already know, citrus fruit and kiwis are packed with vitamin C.
After controlling for several potential confounding factors, the researchers concluded that a high intake of citrus and kiwi fruits was associated with a reduced risk of wheezing, shortness of breath, nocturnal cough and chronic cough. In most cases, the protective effect the vitamin C rich fruits examined in this study was evident even among children whose had citrus fruit and kiwis only one to two times a week.