Our analysis of global evidence shows that being overweight or obese increases the risk of 11 cancers
To date, the research we have analysed for our Continuous Update Project and Second Expert Report has shown that excess body fatness is linked to an increased risk of developing eleven cancers.
Body fatness (marked by body mass index (BMI)), is a key factor influencing health and well being throughout life.
Cancer Increment RR of increased body fatness (95% CI) Report date
Stomach cardia 5 kg/m2 1.23 (1.07-1.40) 2016
Kidney 5 kg/m2 1.30 (1.25-1.35) 2015
Gallbladder 5 kg/m2 1.25 (1.15-1.37) 2015
Liver 5 kg/m2 1.30 (1.16-1.46) 2015
Advanced prostate cancer 5 kg/m2 1.08 (1.04-1.12) 2014
Ovarian 5 kg/m2 1.06 (1.02-1.11) 2014
Endometrial 5 kg/m2 1.50 (1.42-1.59) 2013
Pancreatic 5 kg/m2 1.10 (1.07-1.14) 2012
Colorectal 1 kg/m2 1.02 (1.02-1.03) 2011
Postmenopausal breast cancer 2 kg/m2 1.05 (1.03-1.07) 2010
Oesophageal (adenocarcinoma) No meta-analysis for cohort studies 2007
How does body fatness affect cancer risk?
Body fatness influences the levels of a number of hormones and growth factors. Insulin and leptin are all elevated in obese people, and can promote the growth of cancer cells. In addition, insulin resistance is increased, in particular by abdominal fatness, and the pancreas compensates by increasing insulin production. This hyperinsulinaemia increases the risk of cancers of the colon, endometrium and kidney, and possibly of the pancreas. In men, obesity is related to lower serum testosterone levels, which in turn may be associated with enhanced risk of or adverse outcome in advanced prostate cancer.
Obesity is associated with a low-grade chronic inflammatory state. Obese adipose tissue is characterised with macrophage infiltration and these macrophages are an important source of inflammation in this tissue. The adipocyte (fat cell) produces pro-inflammatory factors, and obese individuals have elevated concentrations of circulating tumour necrosis factor (TNF)-alpha interleukin (IL)-6, and C-reactive protein, compared with lean people, as well as of leptin, which also functions as an inflammatory cytokine. Such chronic inflammation can promote cancer development.
Obesity is a risk factor for non-alcoholic steatohepatitis (NASH), which may progress to cirrhosis and therefore an increased risk of developing liver cancer.
In addition, obesity is a known cause of gallstone formation, and having gallstones increases the risk of gallbladder cancer.
Excess body fat increases the risk of high blood pressure – a factor positively related to the development of kidney cancer.
Excess body fat also puts pressure on the abdomen, which can lead to chronic gastroesophageal reflux, causing cellular and DNA damage around the gastric cardia.
How much cancer could be avoided?
Cancer is often thought to be a mainly inherited disease. This is not so. Some people, and related family members, have inborn high vulnerability to specific cancers. However, to a greater or lesser extent every person has innate or acquired susceptibility to many different diseases. In the greater majority of cases, such susceptibility only leads to actual disease, such as cancer, when driven by external factors. The Continuous Update Project and Second Expert Report identified body fatness as a major risk factor for cancer. Click here to see how many cases of cancer could be avoided if people maintained a healthy weight.