Effect of ozone on FEF25-75 and 95% CI according to genotypes and vitamin C intake. Persistently asthmatic children with vitamin C intake between 30 to 105 mg/day and with GSTM1 null had lower levels of FEF25-75 than children with either GSTM1 positive genotype or dietary vitamin C intake higher than 105 mg/day. Similar situation was observed for Val/Val vs. Ile/Val + Ile/Ile GSTP1 polymorphisms. Linear mixed models were adjusted for age, gender, BMI, height, cohort, time, use of bronchodilator, and previous day’s minimum temperature. Reported values correspond to the effect on FEF25-75 per 60 ppb of ozone.