Insight into weight and cancer survival

Did you know that, for women, the longer you are overweight as an adult, the less likely you are to survive a bowel or breast cancer diagnosis?

Research funded by World Cancer Research Fund has discovered that the longer you are overweight as an adult (aged 20–50) the more likely you are to not survive after being diagnosed with breast or bowel cancer. In fact, every year spent overweight increases the risk, as well as how overweight you are.

Discoveries funded by you

We already know that being overweight or obese increases the risk of at least 12 different types of cancer, and that being overweight or obese has long-term effects on your health, but this large study reveals that weight can also predict your chance of survival after a diagnosis of breast or bowel cancer in women. The next steps are to find out if the same applies to men. So that more people survive after a cancer diagnosis, you can help fund similar research to this one by donating here.

Dr Isabelle Soerjomataram who led the study, said:

"Our research shows that effective prevention of overweight and obesity must start at an early age."

Why does weight affect the risk of cancer?

There is evidence for a number of possible ways that having excess weight increases your chance of developing cancer. All cancers start when the DNA in a cell becomes damaged and is not repaired. This makes it look and behave differently, for example causing the cell to replicate uncontrollably, leading to a tumour.

DNA can be damaged by substances from outside the body such as cigarette smoke, but also by the normal processes of life in the cell. That’s why we have a whole array of defences that repair damaged DNA, or ensure a cell with damaged DNA dies. But obesity seems to affect the balance between the damage that occurs to DNA and how well we can deal with it. The main ways that obesity seems to affect cell behaviour are:


When we are overweight or obese, the excess fat in cells and tissues acts as a stress to the body, which responds by sending white blood cells to the fat tissue, which produces chemicals that lead to a low-level inflammation in the body. Inflammation is simply our immune system’s way of dealing with what it thinks is an attack on our body. Over time, prolonged inflammation leads to DNA damage due to the chemicals that are released to deal with the supposed threat.

Sex hormones

Fat cells can make oestrogen, a female sex hormone, and in post-menopausal women this is the main source (in pre-menopausal women it is the ovaries), so the more fat you have the more oestrogen you have. Oestrogen causes cells in some tissues (ones that have specific receptors for it) to divide and replicate more rapidly. This makes errors in the DNA replication process more likely and can lead to cancer as there are more chances for the DNA to replicate itself incorrectly, causing DNA damage. 


If we are overweight, this leads to changes in our bodies that make them resistant to the action of insulin. Insulin is a hormone that regulates blood sugar but is also a growth hormone which tells the body’s cells to replicate. If the body is resistant to insulin, it will need to make more to compensate. At the same time other insulin-related growth hormones are also released. Together this can cause our cells to replicate, leading to more chances for the DNA to be copied and replicated incorrectly, causing DNA damage.

Often, it’s a combination of all of these factors.

Don’t be scared into submission – take action!

We know that due to modern life, it can be very hard to be a healthy weight. Technology such as cars and computers mean we move less, junk food is cheap, and of course we're bombarded with adverts that encourage us to buy and eat more. That's why our Policy team make recommendations to governments that will make our environments healthier, such as banning junk food marketing aimed at children.

In the meantime, we have some tips that can help you maintain a healthy weight:

  • Reshape your plate
  • Keep an eye on portion sizes
  • Read food labels
  • Be more active

Why not download your free guide, Weight matters: keeping healthy in an unhealthy world, today? 

Of course, it isn’t just a case of knowing you need to be healthier, as it can be very hard to change our habits. Sidonie from our Health Information team shares her struggles with healthy habits and offers some advice on how to make small changes that make a big difference.

And don't forget that EVERY DONATION helps us fund more research and health information, so more people can access the evidence they need to make healthier choices