CORRESPONDENCE

Re: Fruit and Vegetable Intake and Risk of Major Chronic Disease

Anja Olsen, Connie Stripp, Jane Christense, Birthe Lykke Thomsen, Kim Overvad, Anne Tjønneland

Affiliations of authors: Institute of Cancer Epidemiology, The Danish Cancer Society (AO, CS, JC, BLT, AT); Department of Clinical Epidemiology, Aalborg Hospital and Aarhus University Hospital, and Department of Epidemiology and Social Medicine, University of Aarhus (KO)

Correspondence to: Anja Olsen, PhD, Institute of Cancer Epidemiology, The Danish Cancer Society, Strandboulevarden 49, DK-2100 Copenhagen Ø, Denmark (e-mail: anja{at}cancer.dk).

Recently, Hung et al. (1) presented data on the associations between intake of fruits and vegetables and major chronic diseases based on two large American cohorts. They concluded that higher intake of fruits and vegetables might not be associated with a lower risk of cancer. This finding is at odds with a 1997 WHO/IARC report, which stated that an increased intake of fruits and vegetables is one of the most important lifestyle changes needed to reduce the high incidence of cancer in the Western world (2). Consequently, we evaluated whether Hung et al.'s important findings could be reproduced in a different cohort study. In particular, we wanted to investigate the different associations among users and nonusers of dietary supplements shown by Hung et al.

We analyzed the relation between intake of fruits and vegetables and incidence of total cancer in a Danish cohort consisting of 29 068 women and 26 492 men. Of these, 1844 women and 1519 men have been diagnosed with a primary cancer. Details about the cohort have been described previously (3). The analyses of the relationship between the cancer rate and the exposure variables were based on the Cox proportional hazard models. (Proportionality of hazards was evaluated by visual examination of associations across intervals of time, stratified according to sex.)

In unadjusted analyses, higher intake of fruits, vegetables, and juices was associated with lower incidence (of borderline statistical significance) among women and a statistically significantly lower incidence among men (Table 1). We calculated the incidence rate ratio (IRR) associated with 100 g higher daily intake (continuous variable) after adjustment for potential confounders and found no association among women (IRR = 0.99; 95% confidence interval [CI] = 0.97 to 1.01), but a lower incidence (of borderline statistical significance) among men (IRR = 0.96, 95% CI = 0.93 to 0.99). The finding that fruit and vegetable intake is associated with a greater risk reduction in men than in women, which was also seen by Hung et al., could be explained by women in general having higher blood levels of antioxidants (4) and/or by a lack of association between breast cancer risk and fruit and vegetable intake (5,6).


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Table 1.  Breast cancer incidence rate ratios (IRR) and 95% confidence intervals (CI) per 100 g increase in daily intake of fruits, vegetables, and juice among participants in the Diet, Cancer and Health cohort*

 
Hung et al. estimated associations of subtypes of fruits and vegetables with cancer incidence after stratifying for the use of dietary supplements. Nearly all risk estimates among nonusers of dietary supplements were less than 1.00, and the estimate for total intake indicated a borderline statistically significantly reduced risk (risk ratio = 0.92, 95% CI = 0.84 to 1.00), whereas nearly all estimates among users were above 1.00. We found a similar pattern when we stratified participants according to use of dietary supplements at baseline. For women, we saw a borderline statistically significantly reduced risk of cancer only among nonusers. For men, the association among nonusers was stronger than that among users with respect to intake of vegetables and juice, but there was no difference with respect to intake of fruit. Moreover, Hung et al. found that higher intakes of both total citrus fruit and citrus fruit juice—both rich sources of vitamin C—were statistically significantly associated with higher cancer incidence among supplement users.

Increased intake of fruits and vegetables is among the most frequently recommended lifestyle changes. Therefore, the very weak protective associations found by both Hung et al. and us pose challenges to these recommendations. Further, both studies indicate that the use of dietary supplements should receive special attention when associations between diet and cancer are studied.

NOTES

Editor's note: The authors of Hung et al. declined to respond to this Correspondence.

Supported by grants from The Danish Cancer Society and "Europe against cancer": European Prospective Investigation into Cancer and Nutrition (EPIC). "Diet, Cancer and Health" and this substudy were approved by the regional Ethical Committees on Human Studies in Copenhagen and Aarhus and by the Danish Data Protection Agency. Written informed consent was obtained from all participants.

REFERENCES

(1) Hung HC, Joshipura KJ, Jiang R, Hu FB, Hunter D, Smith-Warner SA, et al. Fruit and vegetable intake and risk of major chronic disease. J Natl Cancer Inst 2004;96:1577–84.[Abstract/Free Full Text]

(2) WCRF. Food, Nutrition and the Prevention of Cancer: a global perspective. Washington (DC): World Cancer Research Fund; 1997.

(3) Johnsen SP, Overvad K, Stripp C, Tjonneland A, Husted SE, Sorensen HT. Intake of fruit and vegetables and the risk of ischemic stroke in a cohort of Danish men and women. Am J Clin Nutr 2003;78:57–64.[Abstract/Free Full Text]

(4) Hercberg S, Galan P, Preziosi P, Bertrais S, Mennen L, Malvy D, et al. The SU.VI.MAX Study: a randomized, placebo-controlled trial of the health effects of antioxidant vitamins and minerals. Arch Intern Med 2004;164:2335–42.[Abstract/Free Full Text]

(5) Smith-Warner SA, Spiegelman D, Yaun SS, Adami HO, Beeson WL, van den Brandt PA, et al. Intake of fruits and vegetables and risk of breast cancer: a pooled analysis of cohort studies. JAMA 2001;285:769–76.[Abstract/Free Full Text]

(6) van Gils CH, Peeters PH, Bueno-de-Mesquita HB, Boshuizen HC, Lahmann PH, Clavel-Chapelon F, et al. Consumption of vegetables and fruits and risk of breast cancer. JAMA 2005;293:183–93.[Abstract/Free Full Text]



             
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