Mediterranean diet and asthma in adults: a multicentre case-control study in a general population sample

The relationship between diet, respiratory diseases and the mechanisms underlying their association are still poorly understood. In an adult sample, we investigated the associations between diet quality evaluated by two dietary scores (Italian Mediterranean Index (IMI), Modified Mediterranean Score (MDS)) and asthma and rhinitis prevalence. Additionally, total and differential white blood cells count, as inflammation indicators and two markers of oxidative stress, 8-iso-prostaglandin F2α (8-isoprostane) and 8-oxo-dihydro-deoxyguanosine (8-OHdG), were measured. A total of 1183 subjects (aged 20–84) in the frame of a population-based multi-case-control study were studied: 186 with current asthma (CA), 103 with past asthma (PA), 445 with rhinitis (RN) and 449 controls. Food intake was assessed by using the EPIC Food Frequency Questionnaire. 8-OHdG and 8-isoprostane were measured on spot urine and standardized by creatinine. A higher adherence to IMI was associated with a lower risk of CA (RRR: 0.50; 95%CI: 0.31;0.81; p = 0.005), but not PA or RN. In CA a higher adherence to the Mediterranean diet (MD) was associated with a lower neutrophil percentage out of total leukocytes (p for trend = 0.022 and p = 0.014 for IMI and MDS, respectively). Urinary 8-isoprostane was not associated with the MD adherence in any of the groups. In subjects with CA, those who were highly adherent according to MDS had higher 8-OH-dG urinary concentrations than non-adherents (p = 0.040) and in subjects with PA, they had lower 8-isoprostane than non-adherents (p = 0.026). Our findings suggest that the MD might be a protecting factor for asthma, but not for rhinitis. The link between diet and asthma is probably the reduction in chronic inflammation, whereas oxidative stress does not seem to influence this relationship.