Fruit and vegetable intake may be protective against asthma
Fruit and vegetable consumption may be protective against asthma and other allergies, a recent meta-analysis suggests.
Researchers gathered data from 58 studies to evaluate the association between fruit and vegetable intake, risk of asthma/wheeze, and immune responses. Of these, 30 studies reported a protective effect of high fruit and vegetable consumption on asthma/wheeze, while eight failed to show benefit. Twenty studies showed mixed results revealing negative associations between the risk of asthma/wheeze and fruit or vegetable intake only.
On subgroup analysis, fruit intake was inversely associated with asthma severity (odds ratio [OR], 0.61, 95 percent confidence interval [CI], 0.44–0.87; p=0.005), and wheeze (OR, 0.94, 95 percent CI, 0.91–0.97; p<0.0001). [Nutrients 2017;doi:10.3390/nu9040341]
Vegetable intake was also negatively associated with risk of prevalent asthma (OR, 0.95, 95 percent CI, 0.92–0.98; p=0.003).
The researchers attributed the protective effect of fruits and vegetables on airway inflammation to the combined effects of certain nutrients in fruits and vegetables.
“Fresh fruit[s] and vegetables are rich dietary sources of antioxidants such as vitamin C, E, and β-carotene as well as flavonoids, isoflavonoids, and polyphenolic compounds … Oxidative stress is elevated in asthma and increases further during acute asthma exacerbations, so a high intake of antioxidants may be beneficial,” they said.
Other studies on paediatric asthma, which is predominantly allergic, have also reported improved pulmonary function and decreased chronic respiratory symptoms (eg, allergic rhinitis, wheezing) in children who reported a high consumption of antioxidant-rich foods. [Allergol Immunopathol 2015;43:353-360; Eur Respir J 2011;37:1060-1067]
Additionally, previous evidence showed an increase in airway neutrophils and upregulation of immune and inflammatory response genes including innate immune receptors after withdrawing antioxidant-rich foods from the diet. [Free Radic Res 2008;42:94-102; OMICS 2009;13:355-365] “The major dietary change in these studies was a decrease in fruit and vegetable consumption to a level [that represents] the typical western diet, which is alarming considering the negative consequences in the airways,” said the researchers.
Certain fruit and vegetable allergens might be similar to some pollen allergens and could lead to allergic reactions once consumed, noted the researchers. “[These] may play a critical role in the pollen-fruit/vegetable cross-reactivity,” they added, noting that diet modifications could impact the observed associations between asthma and consumption of certain fruits or vegetables.
“Overall, the findings suggest that high intakes of fruit and vegetables may have beneficial effects in asthma. However, some studies failed to attain similar results,” said the researchers, who called for further trials to ascertain the role of fruits and vegetables in the development and management of asthma.