The Relationship Between Obesity And Breast Cancer Of Women In China:a Prospective Cohort Study

BackgroundAccording to a recent study by the International Agency for Research on Cancer(IARC),breast cancer surpassing lung cancer become the number one cancer in the world in 2020.Among all female cancer In China,the standardized incidence rate and standardized mortality rate of breast cancer were the first and second respectively,and the burden of breast cancer was increasing.Breast cancer is a complex disease,about 10%of its occurrences are genetically related,but nearly 90%are caused by environmental factors.Obesity is a risk factors for many cancers,and the prevalence of obesity in China has increased rapidly over the past three decades,with more than half of Chinese adults being overweight or obese.Therefore,understanding the impact of overweight and obesity on women’s breast cancer and taking appropriate preventive measures are of profound significance to promote women’s health.A systematic review and Meta-analysis indicated that Body Mass Index(BMI)was strongly correlated with postmenopausal women’s risk of breast cancer.Among premenopausal persons,breast cancer was inversely associated with BMI in Europe women but positively associated in the Asia-Pacific women,which suggests possible racial differences in the association between general obesity and breast cancer.Some studies shown that the association between obesity and breast cancer is likely to be mediated by visceral fat,and waist circumference(WC)is a better representative of body fat than BMI.Currently,there were few studies on the association between WC and breast cancer,and the results remained erratic.In addition,only a few studies considered the effect of changes in BMI on breast cancer.In conclusion,the findings regarding obesity and breast cancer risk are inconclusive,and there is a lack of prospective cohort studies to investigate the effect of obesity on breast cancer risk in China.Therefore,the study aims to investigate the association between obesity and breast cancer in Chinese women based on the "Taizhou cohort",and to provide some theoretical support for the health management and prevention of breast cancer in Chinese women.Objectives1.To examine the relationship of general obesity(BMI)and abdominal obesity(WC)with breast cancer,and to analyze it associations in different menopausal groups.2.To investigate the relationship between BMI changes and breast cancer.MethodsThe study population was from the Taizhou cohort of 29,075 women who completed a baseline survey in Taixing City,Jiangsu Province from 2009 to 2016.The survey consisted of three parts:questionnaire,physical examination and biological sample collection.The questionnaire part included basic personal information,socioeconomic status,reproductive history,personal health history and oral hygiene.Examination includes measurement of height,weight,waist circumference and blood pressure.And the biological sample collection included blood,saliva and solid tissue.Detailed information on breast cancer incidence and death was obtained through the Chronic Disease Incidence Surveillance System,the Universal Health Insurance System,and the Death Registration System.Breast cancer was diagnosed according to the International Classification of Diseases 10th revision(ICD-10)code C50.The cohort was follow-up until December 31,2021.A total of 24,892 study subjects were included in the study of obesity and risk of breast cancer development by excluding those with baseline breast cancer and other malignancies,breast cancer within six months of enrollment,and missing or abnormal values of basic information and obesity indicators.Cox proportional risk regression models were used to analyze the risk ratios(Hazard Ratio,HR)of BMI and WC to breast cancer incidence and their 95%confidence interval(95%CI),with adjustment variables including age,education,annual household income level,and age at menarche.Secondly,stratified analyses were conducted according to baseline menopausal status to further explore the effect of obesity on breast cancer in populations with different menstrual status.After excluding those with missing or abnormal values of BMI related indicators at age 20 years,a total of 20298 participants enrolled in the study of the association between changes in BMI and breast cancer.The change in obesity level was assessed by calculating the difference between BMI at age 20 and baseline BMI,and the association between the change in BMI level and breast cancer incidence was investigated by using Cox regression model.Results1.Incidence of breast cancer in the cohortThere were 29075 study subjects in the cohort.By December 31,2021,the follow-up person-years were 267092.30 with a mean incidence density of 103/100,000.2.Association of general obesity and abdominal obesity with breast cancerThe results of a multifactorial Cox proportional risk model showed that in the total population,compared with the normal weight group,the breast cancer HR(95%CI)for the obese group was 1.83(1.27-2.64).Compared with the WC<76 cm group,WC≥87 cm group had a 59%(95%CI:1.10-2.28)increased risk of breast cancer.When stratification by menopausal status at baseline,in postmenopausal women,the risk of breast cancer increased by 81%(95%CI:1.15-2.86)in obese women and 60%(95%CI:1.01-2.57)with WC≥87 cm.For every 5 kg/m2 increase in BMI and every 10cm increase in WC,the HR(95%CI)of breast cancer in postmenopausal women were 1.47(1.15-1.87)and 1.24(1.03-1.49),respectively.In menopausal women,the stratified analysis by age at menopause showed that,the breast cancer HR(95%CI)for the obese group and the WC≥87 cm group were 1.90(1.18-3.08)and 1.68(1.01-2.79),respectively,among women older than 45 years.No statistical association of BMI and WC with breast cancer in non-menopausal women was found in this study.3.Association of dynamic changes in BMI with breast cancerThe risk of breast cancer in the study population increased significantly with increasing relative dynamic change in BMI(P<0.001 for trend).After stratification,in postmenopausal women,the Q3(HR=2.39,95%CI:1.26-4.54)and Q4(HR=2.99,95%CI:1.62-5.52)groups of the BMI relative dynamic had an increased breast cancer risk.However,no significant statistical correlation was observed in non-menopausal women(Q3 HR=1.24,95%CI:0.65-2.36;Q4 HR=1.53,95%CI:0.79-2.96).Conclusion1.For postmenopausal women,maintaining a normal weight and reducing excess abdominal fat may reduce their future risk of breast cancer to some extent.This study did not find that reducing body weight reduced the risk of breast cancer in non-menopausal women.2.There was a significant dose-response relationship between the relative dynamic changes of BMI and the incidence of breast cancer,which suggested that long-term weight management and maintaining a healthy body weight were important for the prevention of breast cancer.