Dietary flavonoids and respiratory diseases: a population-based multi-case control study in Italian adults

Fruit and vegetable intake is associated with lower risk of respiratory diseases. Extensive experimental evidence suggests that bioactive compounds flavonoids might contribute to such a protective effect but this has been seldom investigated in epidemiological studies. Within the Genes Environment Interaction in Respiratory Diseases (GEIRD), a population-based multi-centric multi-case control study in adults, we studied the associations between respiratory diseases and intake of fruits, vegetables, and of 6 major classes of flavonoids. The European Investigation into Cancer and Nutrition Food Frequency Questionnaire was used to ascertain usual dietary intake. A hierarchic outcome variable approach was used to define mutually exclusive diseases, i.e. subjects with asthma (current, CA, n=142; past, PA, n=77), chronic bronchitis (CB, n=45), allergic rhinitis (AR, n=142; non allergic, NAR, n=125) and controls (n=338). Multinomial regression models adjusting for age, sex, centre, body mass index, smoking habit, alcohol intake, education and total energy intake were used to examine the association between dietary exposures (quartiles) and the relative risk ratio (RRR) of being a case. Total fruit intake (g) was associated with a decreased risk of having CB (adjusted RRR=0.33; 95% CI 0.12, 0.86 for the 4th vs 1st quartile). All subclasses of flavonoids studied were negatively associated with risk of CB but these associations did not reach statistical significance. Intake of flavanones was associated with reduced risk of NAR (adjusted RRR=0.25; 95% CI 0.11, 0.56 for the 4th vs. 1st quartile of intake). Flavonoids found in fruits might reduce the risk of CB and NAR in adults.