Does obesity cause cancer?
- Yes, overweight and obesity is the second biggest cause of cancer in the UK - more than 1 in 20 cancer cases are caused by excess weight
- The risk is higher the more weight you gain and the longer you are overweight for
- Keeping a healthy weight reduces the risk of 13 different types of cancer
What’s my risk of developing cancer if I'm overweight or obese?
Being overweight doesn’t mean that you'll definitely develop cancer. But if you are overweight you are more likely to get cancer than if you are a healthy weight. Your exact risk will depend on lots of factors, including things you can't change such as your age and genetics.
Losing weight or avoiding putting on more weight can help reduce the risk of cancer.
People keeping a healthy weight could prevent around 22,800 cases of cancer every year in the UK.
There are lots of other benefits to keeping a healthy weight including having increased energy and reducing the risk of conditions such as heart disease, stroke and osteoarthritis.
Read our top tips to lose weight.
How can overweight and obesity cause cancer?
Extra fat in the body doesn’t just sit there, its active, sending out signals to the rest of your body. These signals can tell cells in our body to divide more often, which can lead to cancer.
The signals released by fat cells can affect:
- Growth hormones- too much body fat can cause levels of growth hormones to rise, which tells cells to divide more often. This raises the chance that cancer cells will develop.
- Inflammation- when there are more fat cells in the body, immune cells go to the area, possibly to remove dead fat cells. This can lead to inflammation, which causes cells to divide more quickly. Over time, this can increase the risk of cancer.
- Sex hormones- after the menopause, fat cells produce the hormone oestrogen. This can make cells in the breast and womb divide more often which increases the risk of cancer developing.
These are the main ways scientists have identified so far, but research continues to find out more about the ways extra body fat can cause cancer.
What types of cancer are linked to obesity?
Overweight and obsity causes 13 different types of cancer. This includes:
- Breast and bowel (two of the most common cancer types)
- Pancreatic, oesophageal and gallbladder (three of the hardest to treat cancers)
- Womb and ovarian
- Kidney, liver and upper stomach
- Myeloma (a type of blood cancer)
- Meningioma (a type of brain tumour)
Does obesity cause cancer in children?
No. There is no link between obesity and cancer in children. Excess weight only causes cancer in adults. But a healthy body weight is important for children too.
Children who are obese are around 5 times more likely to be obese as adults.
It's important to help children be a healthy weight, so they are more likely to be a healthy weight as adults.
There is lots of high-quality research showing the link between excess weight and cancer.
There are consistent results from decades of research involving millions of people. We see more cancer cases in groups that are overweight compared to groups that are a healthy weight.
The risk increases the more weight is gained, so we can be more sure the link is real (this is called a dose-response relationship). And there are good explanations for how extra fat cells in the body could cause cancer. We can confidently rule out other explanations (such as chance or other risk factors).
International organisations like the International Agency for Research on Cancer and the World Cancer Research Fund agree.
A person's risk of cancer depends on lots of different factors. This includes things you can't change like your age and genes. Factors like smoking, obesity and UV rays also affect our cancer risk.
This doesn't mean that everybody who is overweight, smokes or spends too much time in the sun will develop cancer. But, they are more likely to get cancer.
Yes, it can matter. When too much fat is carried around the middle of the body, near the stomach, it may be more harmful. Some research shows that people who carry a lot of fat around their middle are at an even greater risk of certain types of cancers.
It isn't clear exactly why this is, but it could be to do with how quickly certain chemicals from fat can get into the blood.
The NHS recommends trying to lose weight if your BMI is above 25 or your waist circumference is over 94cm (men) or 80cm (women).
Brown, K. F. et al. The fraction of cancer attributable to modifiable risk factors in England, Wales, Scotland, Northern Ireland, and the United Kingdom in 2015. Br. J. Cancer 118, 1130–1141 (2018).
Secretan, B. L. et al. Special Report Body Fatness and Cancer — Viewpoint of the IARC Working Group. (2016). https://www.nejm.org/doi/10.1056/NEJMsr1606602?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dwww.ncbi.nlm.nih.gov
World Cancer Research Fund / American Institute for Cancer Research Diet, Diet, Nutrition, Physical Activity and Cancer: a Global Perspective. A summary of the Third Expert Report. (2018).