An analysis of more than 2,000 studies of obesity and cancer reveals significant links between high body mass index (BMI) and certain cancers.
The study concludes there is strong evidence to support the association between obesity and 11 of the 36 cancers studied, consisting mainly of those related to digestive organs and hormone-related malignancies.
There could be associations between obesity and other cancers, but substantial uncertainty remains because the quality of evidence from studies is not strong, say the international team of researchers, led by Dr Maria Kyrgiou from the department of surgery & cancer and Dr Kostas Tsilidis from the School of Public Health at Imperial College London.
The researchers say confirming the link is important for identifying those at risk. Kyrgiou said: “Evidence of the strength of the associations between obesity and cancer may allow finer selection of people at high risk, who could be selected for personalised primary and secondary prevention strategies.”
Cancer is a leading cause of death worldwide, and the prevalence of obesity has more than doubled over the past 40 years. Previously published evidence supports the association between obesity and some cancers, but some studies may be flawed or biased due to weak study design and conduct.
Therefore, in a bid to determine the quality of evidence and the strength of these associations, the researchers conducted a comprehensive review of studies on obesity and risk of developing cancer.
After a literature search, they identified 204 meta-analyses from 49 publications that analysed obesity measurements – such as body mass index, weight gain, and waist circumference – and 36 cancers and their sub-types.
Of the 95 meta-analyses that included continuous obesity measures, only 13% of associations were supported by strong evidence, meaning the studies had statistically significant results and no suggestion of bias. Other studies were evaluated to have: highly suggestive (18%); suggestive (25%); weak (20%) evidence; and 25% had no evidence of an association
Strong associations were found in studies that examined BMI with oesophageal, bone marrow, and colon (in men), rectal (in men), biliary tract system, pancreatic, endometrial (in pre-menopausal women), and kidney cancers.
Risk of developing cancer for every five-point increase in BMI ranged from 9% for colorectal cancer among men, to 56% for biliary tract system cancer. Risk of post-menopausal breast cancer among women who never used HRT increased by 11% for each five kilograms of weight gain. Risk of endometrial cancer increased by 21% for each 0.1 increase in waist to hip ratio.
Five additional associations were supported by strong evidence when categorical measures of obesity were used. These included weight gain with risk of colorectal cancer risk and BMI with risk of gallbladder, gastric cardia, and ovarian cancer, and mortality from multiple myeloma.
Tsilidis said: “It is now clear that preventing excess weight may reduce the risk of developing certain forms of cancer. With this information, it is crucial that the healthcare system intensifies efforts to reduce the burden of cancer associated with obesity.”
Abstract
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.
Authors
Maria Kyrgiou, Ilkka Kalliala, Georgios Markozannes, Marc J Gunter, Evangelos Paraskevaidis, Hani Gabra, Pierre Martin-Hirsch, Konstantinos K Tsilidis
[link url="http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/newssummary/news_1-3-2017-10-31-54"]Imperial College London material[/link]
[link url="http://www.bmj.com/content/356/bmj.j477"]BMJ abstract[/link]