Do vegetables and fruits reduce the risk of chronic obstructive pulmonary disease? A case–control study in Japan
Introduction
Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality in the world (Murray and Lopez, 1997). Cigarette smoking has been established as the principal risk factor (Celli and MacNee, 2004, McKenzie et al., 2003, Pauwels and Rabe, 2004). According to a review study, while 95% of COPD patients are, or have been, cigarette smokers, about 20% of smokers develop COPD (Madison and Irwin, 1998), implying that other factors may protect against or contribute to the development of this disease. In particular, the risk of COPD may be reduced through an appropriate diet (Sridhar, 1995).
A high intake of fruits is inversely associated with the risk of COPD (Celik and Topcu, 2006, Van Duyn and Pivonka, 2000, Watson et al., 2002) and respiratory symptoms (Butler et al., 2004, Tabak et al., 2001a, Tabak et al., 2001b). A large cohort study in Singapore found that non-citrus fruit (apples, pears and grapes) intake could decrease cough with phlegm, and soy foods appeared to reduce the development of chronic respiratory symptoms, especially productive cough (Butler et al., 2004). A cross-sectional study in the Netherlands similarly observed that solid fruits (apples and pears) were inversely related to the prevalence of COPD symptoms namely chronic cough and breathlessness (Tabak et al. 2001a), whereas an increased fruit consumption (> 180 g/day) appeared to reduce the prevalence of these respiratory symptoms (Tabak et al. 2001b).
The favourable effect of vegetables was also noted in the literature (Celik and Topcu, 2006, La Vecchia et al., 1998, Watson et al., 2002). Two reviews concluded that a high level of fruit and vegetable consumption could enhance ventilatory function and reduce airway obstruction (Schunemann et al., 2001, Smit et al., 1999). Based on the available evidence, it is likely that vegetables can lower the COPD risk, even among smokers (Van Duyn and Pivonka, 2000). On the other hand, two large studies conducted in the Netherlands and Singapore showed no relationship between vegetable intake and the prevalence of respiratory symptoms (Butler et al., 2004, Tabak et al., 2001b).
Little is known regarding the effects of fruits and vegetables on the COPD risk for the Japanese population. The dietary pattern of Japanese adults is very different from those in European countries. In view of the inconsistent findings reported in the literature, it is important to further investigate COPD and breathlessness in relation to fruit and vegetable consumption by conducting a case–control study in central Japan.
Section snippets
Participants
The study was conducted at the outpatient departments of six hospitals in Aichi, Gifu and Kyoto. A total of 300 COPD patients were referred by respiratory physicians in 2006. Diagnosis of COPD was confirmed by spirometry according to standard protocol (Global Initiative for Chronic Obstructive Lung Disease, 2007) with FEV1 / FVC < 0.7, where FEV1 = forced expiratory volume in 1 s, FVC = forced vital capacity, and predicted FEV1 was calculated using the Japanese Respiratory Society's Guidelines (The
Results
Table 1 presents the characteristics of the participants by case–control status and gender. The mean age of the sample was about 66 years, but the mean BMI (five years ago) of COPD patients was lower than that of controls. No significant changes in BMI were found between five years ago and at interview for both case (p = 0.616) and control (p = 0.081) groups. Most participants had high school or below education and were seldom involved in physical activity over the life course. Over 20% of COPD
Discussion
This was the first study to investigate the association between vegetable and fruit consumption and the risk of COPD and breathlessness for the Japanese population. The strengths of the study were the large sample size and the validated measures to assess habitual food consumption. Moreover, lung function spirometry was taken for each participant to ensure correct classification of the case–control status. The majority (80%) of the patients had COPD diagnosed within the past two years and all
Conclusions
In conclusion, an inverse association was found between vegetable consumption and the risk of COPD for Japanese adults, together with a significant dose–response relationship for the breathlessness symptom. More research is needed to determine whether the beneficial effects can be extended to specific vegetable and fruit, and whether increased consumption can improve the mortality rate due to COPD. Dietary intervention methods able to alter dietary behaviour may then be considered (Takahashi et
Conflict of interest statement
The authors declare that there are no conflicts of interest.
Acknowledgments
The authors are grateful to the following persons for assistance with the recruitment of COPD patients: Dr Morihide Ando, Dr Joe Shindo, Dr Takashi Abe (Department of Respiratory Medicine, Ogaki Municipal Hospital, Ogaki, Gifu); Dr Masami Son (Department of Respiratory Medicine, Ichinomiya Municipal Hospital, Ichinomiya, Aichi). Thanks are also due to four anonymous reviewers for their constructive comments.
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