© The Author 2006. Published by Oxford University Press.
CORRESPONDENCE |
Re: Diabetes Mellitus and Risk of Colorectal Cancer in the Singapore Chinese Health Study
Correspondence to: Sandra L. Wong, MD, University of Michigan, Department of Surgery, Division of Surgical Oncology, 1500 E. Medical Center Drive, 3303 CCGC, Ann Arbor, MI 48109-0932 (e-mail: wongsl{at}umich.edu).
I read with interest the recent study by Seow et al. (1) which used data from the Singapore Chinese Health Study to show that individuals with diabetes were more likely to develop colorectal cancer than those without diabetes. These data add to the current body of literature suggesting that impaired glucose tolerance and hyperinsulinemia influence carcinogenesis via insulin pathways.
In that study, 61 320 Singapore Chinese men and women aged 45 to 74 were enrolled in a prospective cohort study between April 1993 and December 1998. Diagnosis of diabetes was based on self-reporting of physician-diagnosed disease. Cancer cases were ascertained through the population-based Singapore Cancer Registry. The authors showed that diabetes was statistically significantly associated with an increased risk of colorectal cancer risk in both men (relative risk [RR] = 1.5, 95% confidence interval [CI] = 1.2 to 2.1) and women (RR = 1.4, 95% CI = 1.0 to 1.9). This association was robust after adjustment for factors such as age, sex, body mass index, cigarette and alcohol use, physical activity, and family history of colorectal cancer.
Recent trends in diet and lifestyle are reflective of Singapore's rapid industrial development and rising affluence. The prevalence of diabetes mellitus in Singapore has increased dramatically over the past few decades, from 1.9% of adults 18–69 years old in 1975 to 4.7% in 1984, 8.6% in 1992, and 9.0% in 1998, and some evidence exists to suggest that these rates may substantially underestimate the prevalence of diabetes, probably because of underdiagnosis (2). The incidence rate of colorectal cancer has also climbed steadily over the past few decades and is now similar to the rates seen in Western countries (3). Because diabetes rates are relatively high and because colorectal cancer is now the most common cause of cancer in Singapore, it would seem that preventing diabetes may help prevent colorectal cancer.
However, the potential impact of the findings of Seow et al. should be examined further. Their results suggest a relatively modest difference in the risk of colorectal cancer—0.66%—between those with diabetes and those without. On the basis of a calculated population attributable risk, I estimate that only 5.7% of colorectal cancer in the population is due to diabetes and could be prevented by eliminating diabetes.
Seow et al. (1) assert that underreporting of diabetes attenuates the true association between diabetes and the risk of colorectal cancer. However, all incident cases of colorectal cancer in their study were identified through the well-maintained national Singapore Cancer Registry. Given the quality of screening services and the incidence rate of colorectal cancer in Singapore, a substantial level underdiagnosis is unlikely. If, in fact, the actual prevalence of diabetes was underreported in this study, we can only expect the modest population attributable risk, considered to be the best measure of impact on the population, to decrease further.
Both diabetes and colorectal cancer have become major challenges to the health of the Singapore population, making prevention efforts critical. However, future studies will be necessary to demonstrate whether reductions in the incidence of diabetes will lead to declines in colorectal cancer incidence.
REFERENCES
(1) Seow A, Yuan JM, Koh WP, Lee HP, Yu MC. Diabetes mellitus and risk of colorectal cancer in the Singapore Chinese Health Study. J Natl Cancer Inst 2006;98:135–8.
(2) Ministry of Health. Epidemiology and Disease Control Department, National Health Survey 1998, Singapore.
(3) Chia KS, Seow A. Lee HP, Sanmugaratnam K. Cancer incidence in Singapore 1993–1997. Singapore Cancer Registry Report No. 5:2000.
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J Natl Cancer Inst 2006 98: 1019-1020.
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