Dietary patterns and adult asthma: population-based case-control study.

BACKGROUND: Epidemiological studies of diet and asthma have focused on relations with intakes of individual nutrients and foods and evidence has been conflicting. Few studies have examined associations with dietary patterns. METHODS: We carried out a population-based case-control study of asthma in adults aged between 16 and 50 in South London, UK. Information about usual diet was obtained by food frequency questionnaire and we used principal components analysis to define five dietary patterns in controls. We used logistic and linear regression, controlling for confounders, to relate these patterns to asthma, asthma severity, rhinitis and chronic bronchitis in 599 cases and 854 controls. RESULTS: Overall, there was weak evidence that a 'vegetarian' dietary pattern was positively associated with asthma [adjusted odds ratio comparing top vs bottom quintile of pattern score 1.43 (95% CI: 0.93-2.20), P trend 0.075], and a 'traditional' pattern (meat and vegetables) was negatively associated [OR 0.68 (0.45-1.03), P trend 0.071]. These associations were stronger amongst nonsupplement users (P trend 0.030 and 0.001, respectively), and the association with the 'vegetarian' pattern was stronger amongst whites (P trend 0.008). No associations were observed with asthma severity. A 'prudent' dietary pattern (wholemeal bread, fish and vegetables) was positively associated with chronic bronchitis [OR 2.61 (1.13-6.05), P trend 0.025], especially amongst nonsupplement users (P trend 0.002). CONCLUSIONS: Overall there were no clear relations between dietary patterns and adult asthma; associations in nonsupplement users and whites require confirmation. The finding for chronic bronchitis was unexpected and also requires replication.

Dietary antioxidants and asthma in adults: population-based case-control study.

A protective role for dietary antioxidants in asthma has been proposed. However, epidemiological evidence to implicate antioxidant vitamins is weak, and data on the role of flavonoid-rich foods and antioxidant trace elements are lacking. We carried out a population-based case-control study in South London, UK, to investigate whether asthma is less common and less severe in adults who consume more dietary antioxidants. Participants were aged 16-50 yr and registered with 40 general practices. Asthma was defined by positive responses to a standard screening questionnaire in 1996, and complete information about usual diet was obtained by food frequency questionnaire from 607 cases and 864 controls in 1997. After controlling for potential confounding factors and total energy intake, apple consumption was negatively associated with asthma (odds ratio [OR] per increase in frequency group 0.89 [95% confidence interval [CI]: 0.82 to 0.97]; p = 0.006). Intake of selenium was also negatively associated with asthma (OR per quintile increase 0.84 [0.75 to 0.94]; p = 0.002). Red wine intake was negatively associated with asthma severity. The associations between apple and red wine consumption and asthma may indicate a protective effect of flavonoids. The findings for dietary selenium could have implications for health policy in Britain where intake has been declining.