| Backgrounds and ObjectiveAs natural environment and lifestyles of people changed, morbidity and mortality of cancer has been a dramatic increase over the past few decades and cancer has become a public health problem worldwide. Most update data from International Agency for Research and Cancer published that there has been 8.2 million cancer deaths worldwide and this number would increase to 19 million until 2025. Among the known risk factors of cancer, excess body weight has drawn wide attention since last century. Body mass index (BMI), which was been released by World Health Organization (WHO) in 1990 is an efficient measurement of population overweight as well as obesity and has been used in a variety of researches in different fields.A large number of epidemiology studies have focused on the association between body mass index and all-cause mortality, but taking cancer mortality as an outcome factor started only in recent years. Relative studies which evaluated this association in China was mostly case-control studies, cohort study or prospective study especially based on the personal health records in Chinese population is not found. To address this issue, this study evaluated the relationship between BMI and the risk of cancer mortality using data from health data system in Ningbo city, in order to provide epidemiology evidence of cancer prevention and control.Materials and MethodsThe personal health records used in this study were from Yinzhou district of Ningbo city, which established between 2004 and 2009, followed by a survey that investigated for personal lifestyle data. All subjects more than 18 years old were included except for those with missing or abnormal data on height and weight. The deadline of the whole study was December 31th in 2014.To define BMI groups of our analysis, we used Chinese standard cutoff points of more than 23.9 kg/m2 for overweight and 27.9 kg/m2 for obesity. In order to be more specific, we then established 8 BMI groups which included the lowest BMI group (<15.0 kg/m2) and highest BMI group (>30.0 kg/m2) and 6 levels in between, each comprising 2.5 BMI units, using the BMI range of 22.6 to 25.0 kg/m2 as reference.The relationship between BMI and the risk of cancer mortality and specific cancer mortality was analyzed with the use of Cox proportional-hazards regression models. We estimated hazard ratios and 95% confidence intervals for difference BMI groups, after adjusting for potential confounders including baseline age, sex, educational level, marital status and lifestyles (smoking, drinking and physical activity). Further analysis including stratified analysis, sensitive analysis was conducted.ResultsAtotal of 372793 (178333 men and 194460 women) participants were included in the analysis.4359 cancer deaths occurred after the mean follow-up of 8.4 years. The total mortality of all cancer was 139.5/105 person-year, and mortality for the top four cancer-specific were 32.3/105 person-year for stomach cancer,31.5/105 person-year for lung cancer,25.3/105 person-year for liver cancer and 9.4/105 person-year for colorectal cancer respectively.In our studied populations, the adjusted hazard ratios and 95% confidence intervals of different BMI ranges except reference group were2.35(1.33-4.32)、1.21(0.97-1.51)、 1.01(0.91-1.12)、1.08(1.00-1.16)、0.73(0.65-0.82)、0.69(0.57-0.84) and 0.47(0.31-0.70)respectively. The results of stratified analysis showed that the effect of BMI on cancer mortality was more significant among elderly population (>60) and overweight group had lower cancer mortality risk among subjects with follow-up more than 4 years.As with the findings for death from specific cancer mortality, lowest BMI range (<15.0 kg/m2) had the highest mortality risk for stomach cancer and colorectal cancer, while overweight can lower stomach cancer, lung cancer, liver cancer and esophagus cancer mortality in men. However, such linkage in women was weak.ConclusionAs the first follow-up study based on the Electronic Healthcare Records, the most common cancer deaths among rolled population was stomach cancer, lung cancer and liver cancer. In conclusion, relative low BMI range (<22.5 kg/m2) would increase cancer mortality risk, while overweight would have protective effect on population with cancer. However, no elevated risk of cancer mortality was seen in obesity people. The mechanism which is able to explain the trend in our study is still unclear. |
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