Effects of antioxidants on asthma

While the prevalence of asthma and allergic diseases continues to rise, the consumption of dietary antioxidants is decreasing around the world.  The western diet is becoming more popular around the world even though it is characterized by a reduction of fresh fruits and vegetables with an increase of processed foods and antioxidant enriched foods. As pulmonary and systemic oxidative stress increase allergic inflammation, dietary or supplemental antioxidants have been proposed to counteract the incidence and morbidity of allergic disease.  Moreno-Macias and Romieu summarize various studies associated with the effects of antioxidants on asthma and allergic diseases (J Allergy Clin Immunol 2014; 133(5): 1237-44).

Meta-analyses of epidemiologic studies of variable quality suggest associations of low dietary intake of antioxidants and increased asthma and allergy. Compared to asthma, few trials have looked at associations between diet and atopic dermatitis, allergic rhinitis, or IgE levels.  Large trials of antioxidant supplementation to prevent cancer suggest an increased mortality with supplementation at least in populations with sufficient dietary intake of antioxidants.  High levels of antioxidants are found in the Mediterranean diet which is associated with a decrease in asthma and allergic disease suggesting high levels of antioxidants in the diet are beneficial. However, antioxidant supplementation may be protective under certain conditions where vulnerable populations have a deficiency in dietary antioxidants and/or are exposed to environmental oxidants. 

The authors explain that while appropriate levels of antioxidants are necessary to eliminate oxidants, the source of the antioxidant intake may be crucial when counteracting oxidative stress. Taken together, these data highlight the importance of antioxidant effects in asthma and allergic diseases and that future studies should focus on the source of antioxidant intake.

Question for the authors:  The source of antioxidants is likely relevant in other inflammatory conditions similar to the cancer study. Being that this sheds more light on the quality of the Western diet, what types of future research do you foresee coming from such important information?

We think that dietary interventions based on food exchange may be useful.  In addition, although following people over time implies big efforts in terms of money and human resources,  it is necessary to understand the disease dynamic taking into account variables that may change over time such as antioxidant intake and life styles. The use of biomarkers instead of surrounding variables would be more informative. Since the source of the antioxidant diet is relevant, this variable should be included as well.  Moreover, since we are in the genomic era, epigenetic,  nutrigenomic and toxicogenomic analyses  will be incorporating relevant information.