| Background:Cancer has been one of the most common non-communicable diseases in China with a dramatic increase of incidence rate in the recent decades. The increase of cancer incidence has put a much larger burden on the developing healthcare systems in China. Published studies showed that body fatness was associated with the increased risk of oesophageal adenocarcinoma and renal cell carcinoma, and cancers of the colon, endometrium, postmenopausal breast etc. However, body mass index (kg/m2) was used in most studies to assess the extent of adiposity but without consideration of body fat distribution. In addition, a few studies on obesity and cancer risk in China mainly based on case-control studies. More importantly, studies in China mainly evaluated the correlation between obesity (BMI mainly) and the risk of single cancer type. The relative risks between obesity and the risk of cancer varied by different sites haven’t be evaluated and compared with each other among certain populations.Objective:To evaluate the association and its strength between BMI, waist circumference, abdominal circumference, hip circumference, waist-to-hip ratio and cancer incidence in a large-scale prospective study.Methods:A dynamic cohort was established on May1,2006. Baseline information on demography, lifestyle, anthropometry such as body height, weight, waist circumference, abdominal circumference and hip circumference, was collected during the first interview, and cancer incidence, mortality and other related outcome information were obtained by both follow-up every two years and searching health-related information databases every year. The population structure from the third national census in1982and Segi’s population standard by WHO were used for the calculation of age-standardized rate (ASR) China and world, respectively. Multivariable Cox proportional-hazards regression model was used to calculate the HRs (hazard ratios) and95%CI (confidence interval) between BMI, waist circumference, abdominal circumference, hip circumference, waist-to-hip ratio and cancer incidence adjusted for age groups (by ten years), educational level, tobacco smoking (smokers and non-smokers), alcohol consumption (drinkers and non-drinkers) and HBsAg status (positive or negative, for liver cancer only) when appropriate. Stratification analysis was carried out on male lung cancer, male liver cancer and female breast cancer by tobacco smoking, HBsAg status and menopausal status respectively. Sensitivity analysis was carried out by excluding cancer cases diagnosed within the first year of follow-up and its results were used for our study.Results:By Dec31,2011, a total of133811subjects, including107065(80.01%) males and26746(19.99%) females, were enrolled in the cohort. There were571098.90person-year (PY) of follow-up and4.27-year of average follow-up period. According to the Guidelines for Prevention and Control of Overweight and Obesity in Chinese Adults, study subjects were divided into underweight (BMI<18.5kg/m2), normal weight (BMI18.5kg/m2-23.9kg/m2), overweight (BMI24.0kg/m2-27.9kg/m2) and obese (BMI≥28.0kg/m2). In males,2402(2.25%) were underweight,45234(42.29%) were normal weight,43902(41.04%) were overweight and15427(14.42%) were obese. Abdominal obesity was account for64.32%(WC≥85cm) or53.69%(WHRS≥0.90). Meanwhile, in females,858(3.21%) were underweight,14071(52.66%) were normal weight,8537(31.95%) were overweight and3253(12.17%) were obese. Abdominal obesity was account for60.50%(WC≥80cm) or58.47%(WHR≥0.85). A total of2069incident cancers cases were collected duringthe follow-up, including1690men and379women. Cancer incidence rate was369.98/100000PYs and331.54/100000PYs in males and females, with128.31/100000PYs and141.48/100000PYs for ASR China and172.51/100000PYs and185.14/100000PYs for ASR World in males and females, respectively. In males, cancer of lung was the most frequently diagnosed cancer with an incidence rate of107.49/100000PYs (ASR China:36.28/100000PYs; ASR World:49.63/100000PYs), followed by cancer of colorectum, liver, stomach and kidney. While in females, cancer of breast was the most incident cancer (incidence rate of100.60/100000PYs, ASR China of38.76/100000PYs and ASR World of51.60/100000PYs), followed by cancer of lung, colorectum, uterus and brain¢ral nervous system. Multivariate Cox proportional-hazards regression model showed that, for the association between BMI and cancer incidence, overweight increased the risk of colon cancer incidence (adjusted HR=1.98,95%CI=1.03-3.82) in males, but decreased the risk of lung cancer incidence in male non-smokers (adjusted HR=0.50,95%CI=0.35-0.72) and bladder cancer incidence (adjusted HR=0.44,95%CI=0.23-0.84), as well as esophageal cancer incidence (adjusted HR=0.50,95%CI=0.25-1.00) in males. Obesity increased the risk of colon cancer incidence (adjusted HR=2.15,95%CI=1.25-6.06) in males and breast cancer incidence in postmenopausal females (adjusted HR=1.97,95%CI=1.01-3.82), but decreased the risk of lung cancer in male non-smokers (adjusted HR=0.57,95%CI=0.33-0.97). For the association between waist circumference and cancer incidence, abdominal obesity (WC≥85cm) might play a protective role in gastric cancer incidence in males (adjusted HR=0.64,95%CI=0.44-0.93). Compared with the lowest quartile in WC, the highest quartile increased the risk of colon cancer incidence (adjusted HR=2.27,95%CI=1.01-5.09) in males, but might play a protective role in lung cancer incidence (adjusted HR=0.75,95%CI=0.56-1.00) in males. For the association between abdominal circumference and cancer incidence, compared with the lowest quartile in AC, the highest quartile might play a protective role in gastric cancer incidence (adjusted HR=0.5S,95%CI=0.35-0.97) in males. For the association between hip circumference and cancer incidence, no risk difference was seen between highest quartile and lowest quartile. For the association between waist-to-hip ratio and cancer incidence, abdominal obesity (WHR≥0.85) play a protective role in breast cancer incidence in postmenopausal females (adjusted HR=0.45,95%CI=0.26-0.77). Compared with the lowest quartile in WHR, the highest quartile might play a protective role in gastric cancer incidence (adjusted HR=0.52,95%CI=0.31-0.85) in males.Conclusion:The association between body fatness and cancer incidence varied by different cancer sites. Obesity increased the risk of colon cancer in males and breast cancer incidence in postmenopausal females, but might play a protective role with lung cancer incidence in male non-smokers. Overweight might play a protective role in lung cancer incidence, bladder cancer incidence and esophageal cancer incidence in males. Abdominal obesity increased the risk of colon cancer in males, but might play a protective role with gastric cancer incidence, lung cancer incidence in males and breast cancer incidence in postmenopausal females. Further follow-up and etiological exploration will help evaluate the association between body fatness and cancer incidence more reliably. |
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