What is diabetes?

Diabetes is a condition where there is too much glucose in the blood. Glucose is a type of sugar. Our bodies use sugar for energy.

The amount of sugar in the blood is usually controlled by the hormone insulin. Insulin is made in a gland called the pancreas.

There are 2 main types of diabetes:

  • type 1 diabetes, where the pancreas does not make any insulin
  • type 2 diabetes, where the pancreas does not make enough insulin or the insulin does not work properly.

Type 2 diabetes is a lot more common than type 1. About 9 in 10 people with diabetes (90%) have type 2.

You can find out more about diabetes from the Diabetes UK website.

Does diabetes cause cancer?

People with diabetes are more at risk of developing certain types of cancer. We do not know exactly why this is.

Research is trying to find out if diabetes treatments affect the risk of developing cancer. At the moment there is no evidence that any diabetes treatments increase the risk. Metformin, one of the more commonly used drugs to treat diabetes, may help lower cancer risk.

If you have diabetes, a healthy lifestyle may reduce your risk of developing cancer.

We have more information to help you with healthy lifestyle choices. Diabetes UK also has some useful information to help you lead a healthy lifestyle.

  • Type 2 diabetes and cancer risk

    Type 2 diabetes and some types of cancer have some similar risk factors. For example, being overweight means there is a higher risk of developing diabetes and cancer of the gullet (oesophagus)bowelbreastwomb and kidney. Both diabetes and cancer are also more common in people as they get older. 

    People with type 2 diabetes have a higher risk of developing cancer of the pancreasliver (primary liver cancer)womb (endometrium)bowel (colon and rectum)bladder or breast

    People with type 2 diabetes have a lower risk of developing prostate cancer. This may be because some men with diabetes have a smaller amount of male hormone (testosterone) in the body.

  • Type 1 diabetes and cancer risk 

    We do not know as much about the risk of developing cancer for people with type 1 diabetes. But they may have a higher risk of developing cancer of the cervix or stomach.

Does cancer cause diabetes?

Your risk of developing diabetes may be higher if you have certain types of cancer. For example, you have a higher risk if you have cancer of the pancreas.

Diabetes and tests for cancer

There are lots of different tests and scans that are used to help diagnose cancer. Some of these tests are also used during treatment and as part of your follow-up care. Many of these tests will not affect your diabetes. Some tests need a bit more planning.

You should contact the hospital before the test and tell them that you have diabetes.

We have more information about managing diabetes when you are having tests and scans.

Planning your cancer treatment

 A team of health professionals will plan your cancer treatment. This team is called a multi-disciplinary team (MDT). Your MDT will not usually include a diabetes specialist doctor or nurse. Your diabetes team will often be asked for advice. Ask your cancer doctor and specialist nurse if they have talked about your treatment with your diabetes team.

Some cancer treatments can affect the amount of sugar in your blood. This means you and your cancer specialist may need to plan cancer treatment more carefully. It may also mean you have to change your diabetes treatment at times.

You may understand your diabetes and how to manage it better than the team treating your cancer. It is important that you talk about your needs and are involved in planning your treatment.

We have more information about diabetes and planning your cancer treatment, including how to prepare if you need to spend time in hospital.

Cancer treatment and diabetes

Different types of cancer treatment can affect diabetes in different ways. We have more information about diabetes and the following treatments:


Clinical trials

Clinical trials try to find new and better treatments for cancer.

All clinical trials have strict guidelines about who can take part. These are known as entry criteria or eligibility criteria. Anyone who wants to take part in a clinical trial must meet these criteria. All trials also have exclusion criteria. These explain who cannot take part. Exclusion criteria help to make sure the people who take part are safe. Exclusion criteria also make sure the results are as accurate as possible.

If you have diabetes, you may not be able to take part in some trials. Your cancer specialist can tell you if you are suitable for a specific trial.

Diabetes and side effects of cancer treatment

Cancer or its treatments can cause side effects that can affect your blood sugars. These include:

  • feeling sick or being sick
  • changes in appetite
  • lack of activity

Because of your diabetes you may be more at risk of some side effects:

  • diarrhoea
  • infection
  • slow wound healing.

We have more information on diabetes and the side effects of cancer treatment.

Advanced cancer

Trying to manage diabetes effectively can be more difficult if you have advanced cancer.

We have more information about advanced cancer and diabetes. 

Your feelings

When you are told you have cancer, you might be overwhelmed by different feelings. It can be very difficult if you are already coping with another condition, such as diabetes. There may be times when you struggle to manage your diabetes. This might be if you are feeling ill because of cancer treatment.

We have more information about feeling lots of different emotions and suggestions for coping with them.

You can also call the Diabetes UK Helpline and talk to trained counsellors. Or you can join a Diabetes UK local group.

This information was produced in partnership with Diabetes UK.
In partnership with Diabetes UK. Know diabetes. Fight diabetes.
Image: Diabetes UK

Date reviewed

Reviewed: 31 January 2020
Next review: 31 January 2023

This content is currently being reviewed. New information will be coming soon.

Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.