Fresh fruit intake and asthma symptoms in young British adults: confounding or effect modification by smoking?

Antioxidant vitamins have been postulated as a protective factor in asthma, The associations between the frequency of fresh fruit consumption in summe r, and the prevalence of self-reported asthma symptoms were investigated. The analysis was based on 5,582 males and 5,770 females, born in England, W ales and Scotland between March 3-9, 1958 and aged 33 yrs at the time of su rvey. The 12-month period prevalence of wheeze and frequent wheeze were inversely associated with frequent intakes of fresh fruit and salad/raw vegetables a nd positively associated,vith smoking and loner social class. After adjustm ent for mutual confounding and set, associations with smoking persisted, bu t those with social class and salad/raw vegetable consumption lost signific ance. The frequency of fresh fruit intake was no longer associated with whe eze after adjustment, but was inversely associated with frequent wheeze and speech-limiting attacks. The association with frequent wheeze differed sig nificantly between smoking groups (never, former, current) and appeared to be confined to exsmokers and current smokers. These findings support postulated associations between infrequent fresh fru it consumption and the prevalence of frequent or severe asthma symptoms in adults. Associations appeared to be restricted to smokers, with effect modi fication as a more likely explanation of this pattern than residual confoun ding by smoking.