Handbook of Vitamin C Research

358Fumi Hirayama and Andy H. Leeto missing or incomplete demographic and lifestyle details. The remaining 278 patients (244men and 34 women) were available for analysis. No statistically significant differences werefound between the included and excluded cases in terms of clinical and other variables.Permission to recruit patients and access to medical records were granted by the participatinghospitals in Japan.During the same period, 400 community-dwelling adults were recruited from the samecatchment areas as the cases. These controls were approached and interviewed at shoppingmalls, community centres or when they attended health checks at hospitals. They wereselected to be frequency matched to the cases by age ( 5 years). The same exclusion criteriaas cases were applied, resulting in 340 eligible controls (272 men and 68 women). Allparticipants underwent spirometric measurements of respiratory function to avoidmisclassification of case-control status. Approval of the study protocol was obtained from theHuman Research Ethics Committee of Curtin University (approval number HR 90/2005) andthe six hospitals in Japan.InterviewA face-to-face interview using a structured questionnaire was administered by the firstauthor to collect information from each participant. Demographic and lifestyle characteristicssolicited included age, gender, weight (kg), height (m), education level (high school orbelow; college or university), cigarette smoking (never smoker; ex-smoker; current smoker)and alcohol drinking status (non-drinker; drinker). For the cases, each interview wasconducted in the presence of their next-of-kin to minimize recall error, and appointment wasmade via their respiratory physician. The purpose of the study was explained to eachparticipant before obtaining their formal written consent. Confidentiality of the informationprovided, and the right to withdraw without prejudice, were ensured and maintainedthroughout the study. All interviews, averaging 30 minutes in duration, took place in thehospital outpatient departments for cases and their place of recruitment for controls.Food Frequency QuestionnaireInformation on habitual food consumption was obtained using a 138-item foodquestionnaire taken from the Japan Public Health Center-based prospective study on cancerand cardiovascular disease (Ishihara et al. 2003a). Its validity and reproducibility had beenestablished for the Japanese population (Ishihara et al. 2003b). The reference recall period fordietary variables was set at 5 years before diagnosis for cases or 5 years before interview forcontrols. The questionnaire asked about the usual consumption of 30 vegetables and 16 fruits.The vegetable items included six pickled vegetables (Chinese radish, green leaf vegetable,plum, Chinese cabbage, cucumber, eggplant), seven cruciferous vegetables (cabbage,Chinese radish, komatsuna, broccoli, Chinese cabbage, leaf mustard, chard or Swiss chard),six green leafy vegetables (spinach, Chinese chive, garland chrysanthemum, bok choi,mugwort, green pepper), four yellow vegetables (carrot, tomato, pumpkin, tomato juice), and