It has been hypothesised that dietary changes associated with a westernised lifestyle may have contributed to the increase in asthma in the developed world. Epidemiological evidence of an inverse association of dietary fruit intake with pulmonary function and respiratory symptoms suggests that dietary antioxidants may modify the development of respiratory disease in susceptible individuals.

Previous studies found that symptomatic asthma in adults is associated with a low dietary intake of fruit, the antioxidant nutrients vitamin C and manganese, and low plasma vitamin C levels.

A new meta-analysis review also suggests that a low dietary intake of vitamin A and C increases the risk of asthma. 40 studies (up to November 2007) of asthma, wheeze, or airway responsiveness in relation to intakes and serum concentrations of vitamins A, C and E were included in this latest review.

Dietary vitamin A intake was significantly (182µg/day) lower at in people with asthma compared to those without asthma; and vitamin A intake was 344µg/day lower in patients with severe asthma compared to those with mild asthma. Lower serum levels of vitamin C were also associated with an increased occurrence of asthma. Vitamin E intake was generally unrelated to asthma status but was significantly lower in people with severe asthma compared to people with mild asthma.

These findings suggest that diet may be a potentially modifiable risk factor for the development of asthma.

Sources: Thorax April 2009 online; Thorax 2006;61;388-393