Department of Community, Occupational and Family Medicine, Faculty of Medicine, National University of Singapore.
Dr Jeannette Lee, Department of Community, Occupational and Family Medicine, Faculty of Medicine MD3, National University of Singapore, 16 Medical Drive, Singapore 117597. E-mail: cofleejm{at}nus.edu.sg
SirsThe impact of body weight on disease and mortality has been assessed in only a few cohort studies in indigenous Asian groups.1,2 Body mass index (BMI), calculated as weight in kilograms/height in metres2, is used as an indicator of body weight. According to the WHO classification, BMI values are: underweight (18.5), normal weight (18.524.9), overweight (2529.9) and obese (30). We report a prospective study assessing the effect of being overweight on all-cancer incidence and all-cause mortality in Chinese, Malays and Asian Indians in Singapore.
Participants, methods, results
A prospective study (ending on 31 December 1997) was conducted using two previous population-based cross-sectional studies of healthy individuals (the Thyroid and Heart Study3 and the National University of Singapore Heart Study4). End-points were obtained by electronic linkage to: (1) The Cancer Registry, (2) The Death Registry. The parliamentary electoral register of 1997 was used to confirm that other subjects were alive and living in Singapore. Only 128 people (6%) were lost to follow-up and excluded from the analysis.
Overweight individuals (overweight and obese categories combined, i.e. BMI 25.0) were compared to normal weight individuals (BMI 18.524.9). Coxs proportional hazards regression model was used to derive hazard ratios (HR), adjusted for age (in years as a continuous variable), ethnic group (Chinese, Malay and Asian Indian), and other risk factors (physical activity, smoking and alcohol) using SPSS version 10.
During a follow-up period of 15 years (mean 13.7 years), 21 132.1 person-years were observed, with individuals in the normal weight category contributing 15 747.9 and those in the overweight category contributing 5384.2 person-years.
Table 1 shows that, after adjustment for all risk factors, overweight people had an increased risk of cancer compared to those of normal weight, both for males (HR 1.5) and females (HR 1.4). Table 1
also shows that overweight females had an increased risk of all-cause mortality (HR 2.4). Overweight males had increased all-cause mortality (HR 1.2), but it was less than in females.
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Although the relationship of BMI and all-cancer incidence has been assessed in a few cohort studies in Caucasian populations,5 this is the first such study in an indigenous Asian population. This study indicates that, even after adjustment for other risk factors, overweight people have a greater risk of developing cancer than those of normal weight in both genders (about one and a half times). Overweight was also associated with increased all-cause mortality in females (about two and a half times). To our knowledge no studies have assessed this in Asian women.
The findings of this study are of concern in view of the increasing prevalence of obesity. Further follow-up of a larger cohort currently in progress in Singapore should fully determine the effect of being overweight on mortality and incidence of individual cancers and other diseases in this Asian population.
Acknowledgments
Funding: National University of Singapore Research Fund: R 186000054720/
References
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