肥胖与乳腺癌等十一种癌症密切相关
2017年2月28日，《英国医学杂志》在线发表伦敦帝国学院、西伦敦妇科癌症中心、夏洛特皇后和切尔西医院、哈默史密斯医院、希腊约阿尼纳大学、法国里昂国际癌症研究机构、英国兰开夏教学医院、兰卡斯特大学的研究报告，发现肥胖可增加11种癌症的发生风险，包括乳腺癌、卵巢癌、子宫内膜癌、食管腺癌、贲门癌、胆道癌、肾癌、胰腺癌、结肠癌、直肠癌、多发性骨髓瘤。
该研究从PubMed、Embase、Cochrane数据库检索出204篇包括肥胖、体重增加、腰臀围比值与36种癌症相关性的荟萃分析。
结果发现，当体重指数超标，食管、骨髓、胆道系统、胰腺、肾脏的癌症发生风险上升，男性结肠癌、直肠癌、绝经前女性子宫内膜癌的发生率也增加。
通常，体重指数（体重÷身高²）18.5～24.9kg/m²为正常体重，25～29.9kg/m²为超重，＞30kg/m²为肥胖，＞40kg/m²为病态肥胖。
对于男性而言，体重指数每增加5kg/m²，直肠癌、胆道癌的风险分别增加9%、56%。
对于女性而言，体重每增加5kg，绝经后患乳腺癌的风险增加11%；腰臀围比值每增加0.1，子宫内膜癌的风险增加21%。
除了这11种癌症，其他肿瘤也可能与肥胖有相关性，但是不确定性很大。既往研究结果可能夸大了肥胖与癌症的相关性，或者两者相关性太低以至于无法排除偶然性。但是，与消化系统、女性激素分泌相关的恶性肿瘤与肥胖有很强的相关性。
该研究的局限在于未分析能够证明肥胖直接导致癌症的对照研究。肥胖对癌症的影响，会因为身体部位不同而存在差异。将来的研究应更关注体内脂肪的变化，以便更好理解肥胖如何直接影响癌症或者其他疾病。
1997年，世界卫生组织（WHO）首次将肥胖定义为疾病。2000年，美国食品药品管理局（FDA）承认肥胖是一种疾病。近年来，越来越多的研究基于大量的流行病学数据，明白无疑地承认肥胖是一种疾病。更重要的是，肥胖影响人体的正常生理功能、威胁人类的健康，每年至少有280万人死亡可归咎于超重或肥胖。
癌症是全球的第二大死因，2015年880万人因为癌症而去世。世界卫生组织数据显示，约1/6的死亡原因是癌症。其中，1/3的癌症死亡源于5种行为和饮食风险因素：体重指数高、水果和蔬菜摄入量低、缺乏运动、吸烟、饮酒。
根据世界卫生组织（WHO）的统计，全球约有19亿成年人超重或者肥胖。也就是说，10个成年人中就有4个人超重，至少1个人属于肥胖。
2016年4月，《柳叶刀》发表的研究报告以40年统计数据揭示了全球肥胖问题。全球肥胖人口从1975年的1亿5百万上升至2014年的6亿4千1百万，远超过体重过轻者。其中，中国和美国是全世界肥胖人数最多的国家。2017年1月，福布斯发表的文章表明，中国肥胖人口的数量已经赶超美国，这无疑大大增加了国家的经济和医疗负担。这主要与中国饮食结构转变有关联，例如高糖、高胆固醇、反式脂肪食物摄入量的增加。这些研究数据无一不在提醒：对于那些超重或肥胖的人而言，减少一些体重或许可以降低癌症风险。
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BMJ. 2017 Feb 28;356:j477.
Adiposity and cancer at major anatomical sites: umbrella review of the literature.
Kyrgiou M, Kalliala I, Markozannes G, Gunter MJ, Paraskevaidis E, Gabra H, Martin-Hirsch P, Tsilidis KK.
Imperial College London, London, UK; West London Gynaecological Cancer Centre, Queen Charlotte's and Chelsea Hospital, Hammersmith Hospital, Imperial Healthcare NHS Trust, London, UK; University of Ioannina School of Medicine, Ioannina, Greece; International Agency for Research on Cancer, Lyon, France; University of Ioannina, Ioannina, Greece; Lancashire Teaching Hospitals, Preston, UK; University of Lancaster, Lancaster, UK.
OBJECTIVE: To evaluate the strength and validity of the evidence for the association between adiposity and risk of developing or dying from cancer. Design Umbrella review of systematic reviews and meta-analyses.
DATA SOURCES: PubMed, Embase, Cochrane Database of Systematic Reviews, and manual screening of retrieved references. Eligibility criteria Systematic reviews or meta-analyses of observational studies that evaluated the association between indices of adiposity and risk of developing or dying from cancer. Data synthesis Primary analysis focused on cohort studies exploring associations for continuous measures of adiposity. The evidence was graded into strong, highly suggestive, suggestive, or weak after applying criteria that included the statistical significance of the random effects summary estimate and of the largest study in a meta-analysis, the number of cancer cases, heterogeneity between studies, 95% prediction intervals, small study effects, excess significance bias, and sensitivity analysis with credibility ceilings.
RESULTS: 204 meta-analyses investigated associations between seven indices of adiposity and developing or dying from 36 primary cancers and their subtypes. Of the 95 meta-analyses that included cohort studies and used a continuous scale to measure adiposity, only 12 (13%) associations for nine cancers were supported by strong evidence. An increase in body mass index was associated with a higher risk of developing oesophageal adenocarcinoma; colon and rectal cancer in men; biliary tract system and pancreatic cancer; endometrial cancer in premenopausal women; kidney cancer; and multiple myeloma. Weight gain and waist to hip circumference ratio were associated with higher risks of postmenopausal breast cancer in women who have never used hormone replacement therapy and endometrial cancer, respectively. The increase in the risk of developing cancer for every 5 kg/m² increase in body mass index ranged from 9% (relative risk 1.09, 95% confidence interval 1.06 to 1.13) for rectal cancer among men to 56% (1.56, 1.34 to 1.81) for biliary tract system cancer. The risk of postmenopausal breast cancer among women who have never used HRT increased by 11% for each 5 kg of weight gain in adulthood (1.11, 1.09 to 1.13), and the risk of endometrial cancer increased by 21% for each 0.1 increase in waist to hip ratio (1.21, 1.13 to 1.29). Five additional associations were supported by strong evidence when categorical measures of adiposity were included: weight gain with colorectal cancer; body mass index with gallbladder, gastric cardia, and ovarian cancer; and multiple myeloma mortality.
CONCLUSIONS: Although the association of adiposity with cancer risk has been extensively studied, associations for only 11 cancers (oesophageal adenocarcinoma, multiple myeloma, and cancers of the gastric cardia, colon, rectum, biliary tract system, pancreas, breast, endometrium, ovary, and kidney) were supported by strong evidence. Other associations could be genuine, but substantial uncertainty remains. Obesity is becoming one of the biggest problems in public health; evidence on the strength of the associated risks may allow finer selection of those at higher risk of cancer, who could be targeted for personalised prevention strategies.
PMID: 28246088
DOI: 10.1136/bmj.j477