While it is now commonly known that smoking can play a major role in the development of cancers such as lung and throat, and exposure to UV light increases the risk of skin cancers, many people are still unaware of the link between obesity and cancer. The Centers for Disease Control and Prevention (CDC) estimates that >50% of Americans do not know that being overweight or obese can increase their risk of cancer.
Obesity and cancer: Definitions
Cancer is a term used to define a collection of diseases related to the uncontrolled division of abnormal cells. These cancer cells can invade neighboring tissues, and have the ability to spread, via the lymph system and bloodstream, to other parts of the body.1
What is cancer? Credit: BioDigital, Inc.
Body mass index (BMI) is an index of weight-for-height and is calculated by dividing a person's weight (kg) by the square of his/ her height in meters (m2). ‘Obese’ is the term used to classify individuals over 20 years-of-age with a BMI >30.0 kg/m2. ‘Normal-weight’ is classified as 18.5–24.9 kg/m2. 2
Obesity and cancer: What is known about the link?
Cancer Research UK predicts that “more than 1 in 20 cancers in the UK are linked to being overweight or obese.” A growing amount of evidence proposes that several types of cancer are more common in overweight or obese people and that cancer risk is increased in those with higher body fat. Study data from the GLOBOCAN project estimated that, in 2012 in the United States, ~28,000 new cases of cancer in men and ~72,000 in women were associated with being obese or overweight.3
Some examples of cancers influenced by higher mounts of body fat include:
- Endometrial cancer (women only): Obese women are 2-4 times more likely to develop endometrial cancer compared to those of a normal-weight.4
- Liver cancer: Overweight or obese individuals are up to twice as likely to develop liver cancer, compared to normal-weight individuals. A stronger link is observed in men compared to women.5,6
- Kidney cancer: The risk of developing the most common form of kidney cancer, renal cell carcinoma, is almost twice as likely in overweight or obese individuals compared to normal-weight individuals.7
- Pancreatic cancer: Compared to normal-weight individuals, overweight or obese individual are 1.5 times more likely to develop cancer of the pancreas.8
Risk of developing cancer increases with the more weight you gain. Risk is also influenced by the amount of time you are overweight for – the longer you are overweight, the greater the risk.
Overweight and Obesity are Associated with Cancer. Credit: Centers for Disease Control and Prevention (CDC)
Obesity and cancer: What research is currently being conducted?
A number of studies are currently focused towards understanding the mechanisms linking obesity and cancer. Several factors associated with obesity and Type-2 diabetes, including;
- hyperinsulinemia (excess insulin levels in the bloodstream)
- hyperglycemia (high blood sugar levels)
- dyslipidemia (abnormal amounts of lipids in the bloodstream)
- adipokines and cytokines (cell signaling proteins)
- and the gut microbiome (microorganisms living in the digestive tract)
The National Cancer Institute (NCI) launched the Transdisciplinary Research on Energetics and Cancer (TREC) 2011–2016 initiative, which included several research centers. The centers were tasked with investigating; different biological mechanisms linking excess adiposity (obesity) with cancer, how physical activity and energy balance can influence body weight and carcinogenesis, and the impact of exercise, weight control and behavioral interventions on cancer survival.
Cancer Research UK has summarized key facts based on evidence from many scientific studies investigating the association between cancer risk and obesity, for several different cancer types.