Insight into weight and cancer survival

Weight measuring deviceDid 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 13 different types of cancer. We also know that being overweight or obese has long-term effects on your health.

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.

“Our research shows that effective prevention of overweight and obesity must start at an early age.” Study leader, Dr Isabelle Soerjomataram

Why does weight affect the risk of cancer?

There is evidence 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 in a different way – for example the DNA might cause the cell to replicate uncontrollably, leading to a tumour.

Substances from outside the body – such as cigarette smoke – and the normal processes of life in the cell can damage DNA. That’s why we have a variety 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 three main ways that obesity seems to affect cell behaviour are:

1. Inflammation

When we are overweight or obese, the excess fat in cells and tissues acts as a stress to the body. The body responds by sending white blood cells to the fat tissue. This tissue 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, inflammation will damage DNA 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). In other words, 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 at a quicker rate. This makes errors in the DNA replication process more likely. This, in turn, can lead to cancer, because there are more chances for the DNA to replicate itself incorrectly, damaging itself.


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, and 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. This will lead to more chances for the DNA to be copied and replicated incorrectly, and cause 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 to make our environments healthier. These include banning junk food marketing aimed at children.

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

> Download your free guide: Weight matters: keeping healthy in an unhealthy world

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.