Beyond The Abstract - Micronutrient Intake And Risk Of Urothelial Carcinoma In A Prospective Danish Cohort

Main Category: Urology / Nephrology
Also Included In: Nutrition / Diet;  Cancer / Oncology
Article Date: 10 Sep 2009 - 5:00 PDT

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UroToday.com - Approximately 90% of all bladder cancers are urothelial carcinomas, originating in the epithelial bladder cells. A preventive role of micronutrients against development of urothelial carcinomas seems plausible, since they have a range of potential anti-carcinogenic effects and may thus inhibit carcinogenic actions in the bladder epithelium, as they come into direct contact with this when concentrated in and excreted through the urine.

So far, however, very few studies on the role of micronutrients in bladder cancer etiology have been conducted, providing no clear conclusions.

The prospective "Diet, Cancer and Health" cohort constituted a valid study population to explore a potential association in, as all participants provided detailed information on micronutrient intake from the diet as well as from supplements at baseline. Furthermore, information on vital status and identification of incident cases during the study period was almost complete because information was available from the Central Population Registry as well as the Danish Cancer Registry, which registers all cancers diagnosed in Denmark.

No previous study has shown a protective effect of dietary beta-carotene on bladder cancer. But our finding of such an association mirrors the finding of a protective role of dietary beta-carotene against lung cancer in a range of observational studies.(1) Since lung- and bladder cancer are both to a high degree smoking-related, it seems plausible that a similar preventive effect should also exist with beta-carotene in bladder cancer.

However, when considering studies on supplemental beta-carotene and lung cancer, some experimental studies have, contrary to observational studies, found an increased lung cancer risk with supplemental beta-carotene,(2) indicating a potentially different mechanism of beta-carotene by source. This may be the case for bladder cancer as well, where an experimental study also found an increased risk with supplemental beta-carotene.(3) In our study, we found no association between urothelial carcinoma and supplemental beta-carotene intake, but the consumption frequency of supplemental beta-carotene was very limited in our cohort (2.5 %), which may explain the lack of association.

The differing results in the literature with regard to micronutrient source, underscores the importance of evaluating the micronutrient source in future studies of micronutrients and urothelial carcinoma. It is possible that a source-specific effect exists, where a dietary micronutrient intake may be beneficial, but a supplemental intake harmful or not associated with risk. Such an association may be explained by the different bio-availability of micronutrients in supplements compared to in the diet, or by the much higher doses consumed through supplements.

Our finding of a protective effect of dietary beta-carotene against urothelial carcinoma, especially among smokers, who are at an increased risk of disease, is a promising finding which merits further research in the field. It is however important to consider the possibility that the finding of a beneficial effect of dietary, but not supplemental beta-carotene, may also be explained by the fact that beta-carotene in itself is not the active substance, but that it functions as a proxy for co-existing factors in the diet, which produces the true effect. Future research in the field should thus take this into account by including beta-carotene in low doses in experimental studies to test if it really is the true, bioactive component.

Written by by Nina Roswall, M.Sc., PhD-student as part of Beyond the Abstract on UroToday.com.

References

1. van PG(1996) Epidemiological evidence for beta-carotene in prevention of cancer and cardiovascular disease. Eur J Clin Nutr 50 Suppl 3: S57-S61.
2. Omenn GS(2007) Chemoprevention of lung cancers: lessons from CARET, the beta-carotene and retinol efficacy trial, and prospects for the future. Eur J Cancer Prev 16: 184-91.
3. Cook NR, Le IM, Manson JE, Buring JE, Hennekens CH(2000) Effects of beta-carotene supplementation on cancer incidence by baseline characteristics in the Physicians' Health Study (United States). Cancer Causes Control 11: 617-26.

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