Handbook of Vitamin C Research

Vitamin C Intake by Japanese Patients… 363Several limitations should be considered in conjunction with the findings. Habitualdietary assessment was based on self-report. Responses from the COPD patients inevitablyincurred some recall bias due to possible memory and cognitive loss as a consequence oftheir disease. Therefore, face-to-face interviews were conducted in the presence of patients‘next-of-kin to increase the response rate and to improve the accuracy of their answers.Moreover, data were collected solely by the same investigator (first author) in order toeliminate inter-interviewer bias. Although the control subjects were recruited from the samecatchment areas as the cases and should be representative of the Japanese elderly population,the possibility of selection bias still existed because of their voluntary participation in thestudy. Information bias, however, was unlikely since all participants were blinded to thestudy hypothesis. Another limitation was the exclusion of dietary supplements towards thecalculation of total vitamin C intake. There are many types and brands of vitamin C andmultivitamin supplements available in the market, with different strength and dosage, so thatestimation of intake amount from these sources is difficult. Consequently, the observedfindings cannot be generalized to other populations, especially in view of the relatively smallnumber of female participants recruited into the study.ConclusionSmoking is acknowledged as the major cause of COPD, but evidence has suggested thatvitamin C might protect the lungs from oxidative damage by cigarette smoking (Smit 2001).The present case-control study found Japanese COPD patients had lower dietary vitamin Cintake than their counterparts without the disease. More research is required to ascertain theprotective role of vitamin C, before its incorporation into dietary guidelines and nutritionalsupplementation therapy for pulmonary rehabilitation. Besides experimental research, clinicaltrials and long-term prospective cohort studies are recommended to provide laboratory andepidemiological evidence of the beneficial effect of vitamin C on both the risk and mortalityrate of COPD.AcknowledgmentsThe authors are grateful to the Japanese respiratory physicians for recruitment of COPDpatients, and to all participants who volunteered their time for the project.References[1] Bestall, JC, Paul, EA, Garrod, R, Garnham, R, Jones, PW & Wedzicha, JA 1999,'Usefulness of the Medical Research Council (MRC) dyspnoea scale as a measure ofdisability in patients with chronic obstructive pulmonary disease', Thorax, vol. 54, no.7, pp. 581-6.