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.

Peanut, milk and wheat intake during pregnancy is associated with reduced allergy and asthma in children

The relationship between maternal diet and childhood allergy and asthma is controversial.  Not long ago, the American Academy of Pediatrics advised that maternal dietary restrictions are not necessary with the possible exception of excluding peanuts.  Subsequent systematic reviews concluded that the evidence was inadequate to support any dietary restrictions during pregnancy. In fact, recent research suggests that fetal exposure to common food allergens may be beneficial. Bunyavanich et al examined the associations between maternal intake of common childhood food allergens during pregnancy and childhood asthma and allergies (J Allergy Clin Immunol 2014; 133(5): 1373-1382).

 

The authors studied a healthy pre-birth cohort of 1277 mother-child pairs from the United States and used food frequency questionnaires administered during pregnancy. Children were assessed for food allergy, asthma, allergic rhinitis, and atopic dermatitis by questionnaire and serum specific IgE levels at a mean age of 7.9 years. They discovered that higher maternal peanut intake during the first trimester was associated with 47% reduced odds of peanut allergic reaction. Higher milk intake during the first trimester was associated with reduced asthma and allergic rhinitis, while higher maternal wheat intake during the second trimester was associated with reduced atopic dermatitis. The authors discuss that the first trimester is a formative period of fetal immune development and the mother’s diet may influence helper T cell differentiation as well as fetal airway differentiation. 

The results of this study do not support avoidance of specific foods during pregnancy to prevent allergy and asthma in children.  The authors conclude that the inclusion of peanut, milk, and wheat during pregnancy could be beneficial for the prevention of allergic diseases.

Exposure to food allergens through inflamed skin promotes intestinal food allergy via the TSLP-basophil axis

Along with all allergic diseases, the prevalence of food allergies has increased markedly in recent decades in industrialized nations. An estimated 5% of children and up to 4% of adults are living with food allergy and the fear of having a life threatening allergic reaction. Incidentally, atopic dermatitis (AD) is a known risk factor for developing food allergies later in life. However, the mechanisms through which antigen sensitization in the skin can predispose to allergic inflammation in the intestine remain unclear. Considering AD skin lesions are associated with elevated thymic stromal lymphopoietin (TSLP) expression and basophil infiltration, Noti et al determined that TSLP-elicited basophils promote antigen-induced intestinal food allergy (J Allergy Clin Immunol 2014; 133(5): 1390-99).

 The authors employed a new model of food allergy by sensitizing mice to food antigens on an AD-like skin lesion that predisposed to allergic inflammation in the intestine upon oral antigen feeding. Oral antigen exposure of skin-sensitized mice resulted in antigen specific IgE responses, type-2 inflammation and the accumulation of mast cells in the intestine. In addition to intestinal food allergy, mice also developed eosinophilic esophagitis (EoE)-like disease, a food allergy related disorder. They determined that antigen-induced food allergy is dependent on TSLP that elicits basophils to promote antigen-specific Th2 cytokine responses. Furthermore, the authors demonstrate that TSLP-elicited basophils are both necessary and sufficient to promote IgE-mediated intestinal food allergy in their model.

Despite the challenges associated with mouse models, Noti and colleagues have provided significant insight into mechanisms that mediate food allergy by using  a novel animal model that mimics some characteristics of human disease.  Targeting the TSLP-basophil axis may offer a novel therapeutic approach to treatment and prevention of food allergy.