We aimed to examine missing data in FFQ and to assess the effects on estimating dietary intake by comparing between multiple imputation and zero imputation.

We used data from the Okazaki Japan Multi-Institutional Collaborative Cohort (J-MICC) study. A self-administered questionnaire including an FFQ was implemented at baseline (FFQ1) and 5-year follow-up (FFQ2). Missing values in FFQ2 were replaced by corresponding FFQ1 values, multiple imputation and zero imputation.

A methodological sub-study of the Okazaki J-MICC study.

Of a total of 7585 men and women aged 35–79 years at baseline, we analysed data for 5120 participants who answered all items in FFQ1 and at least 50% of items in FFQ2.

Among 5120 participants, the proportion of missing data was 3·7%. The increasing number of missing food items in FFQ2 varied with personal characteristics. Missing food items not eaten often in FFQ2 were likely to represent zero intake in FFQ1. Most food items showed that the observed proportion of zero intake was likely to be similar to the probability that the missing value is zero intake. Compared with FFQ1 values, multiple imputation had smaller differences of total energy and nutrient estimates, except for alcohol, than zero imputation.

Our results indicate that missing values due to zero intake, namely missing not at random, in FFQ can be predicted reasonably well from observed data. Multiple imputation performed better than zero imputation for most nutrients and may be applied to FFQ data when missing is low.

Increasing childhood asthma rates may be due to changing dietary lifestyle. We investigated the association of dietary intake of antioxidant vitamins and fatty acids with asthma in Japanese pre-school children.

Cross-sectional study.

School-based survey on lifestyle/diet and health status in children in Japan.

Parents of 452 children aged 3–6 years completed a questionnaire on the children's and parents’ lifestyle and demographics. Children were classified into asthma cases and non-asthma cases in accordance with the ATS-DLD (American Thoracic Society and Division of Lung Diseases of the National Heart, Lung, and Blood Institute) questionnaire. Children's diet was assessed using a 3 d dietary record completed by parents. Children's age, sex, BMI, history of food allergy, maternal age, parental history of allergy, maternal education, family size and second-hand smoking were included as covariates. Logistic regression models were used to examine the association between children's diet and asthma.

Compared with children with the lowest intake tertile for vitamin C and vitamin E, those in the highest were significantly inversely associated with asthma; adjusted OR (95 % CI) were 0·35 (0·14, 0·88) and 0·32 (0·12, 0·85), respectively. A statistically significant trend was also observed. Fruit intake showed an inverse but insignificant association with asthma. There were no associations of any type of fatty acids with asthma.

These data suggest that children with high intakes of vitamins C and E may be associated with a reduced prevalence of asthma.