Diabetes and cancer
What is diabetes?
Diabetes is a condition where there is too much glucose in the blood. Glucose is a type of sugar.
The amount of sugar in the blood is controlled by a hormone called insulin.
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 it makes does not work properly – this is called insulin resistance.
We need insulin to live. Insulin is made by the pancreas. Insulin allows the glucose in the blood to enter cells and fuel the body.
Position of the pancreas
Type 2 diabetes is a lot more common than type 1. About 9 in 10 people with diabetes (90%) have type 2. Diabetes UK has more information about causes and symptoms of diabetes.
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, for example if you need to not eat (fast) before a test. You should contact the hospital before the test and tell them that you have diabetes. They can tell you how to prepare for any tests and scans.
We have more information about managing diabetes when you are having tests and scans.
Planning your cancer treatment
Some cancer treatments and some types of tests can affect the amount of sugar in your blood. You and your cancer team may need to talk about how this could affect your treatment plan.
You may need some extra support to help you manage diabetes during cancer treatment. Before your cancer treatment starts, it is important to contact the health professional who normally helps you manage your diabetes.
You may understand how to manage your diabetes better than your cancer team. It is important that you are involved in decisions about your treatment plan. Make sure you tell your cancer team about any preferences and what you need.
HBA1c blood test
Ask your cancer doctor or nurse about having a blood test called an HbA1c before you start your treatment. They may also do this test regularly during your treatment. An HbA1c test shows your average blood sugar levels over the last 2 to 3 months. This helps doctors to monitor how the treatment is affecting your blood sugar levels.
Going into hospital
If you need to go into hospital, your blood sugar levels may be higher or lower than usual while you are in hospital. This can happen because you are being less active and eating different food. It can also be caused by the stress of being in hospital or if you have an infection. Your blood sugars will be checked regularly. Your doctors may need to adjust your diabetes treatment. They will talk to you about this first.
If you need to go into hospital for any tests or treatment, it is important to bring:
- your diabetes medication
- any diabetes equipment
- food and snacks.
If you feel well enough, you can usually carry on testing and managing your own diabetes while you are in hospital. If you are not feeling well enough or need some support, the nurses can help you.
Managing cancer and diabetes
During cancer treatment, you will need to check your blood sugar levels regularly. You may need to change your diabetes medicine to manage the amount of sugar in your blood. Your diabetes team or your cancer team can help you with this.
While you are having cancer treatment, it is important to try to keep your blood sugar level in a safe range. The diabetes team can tell you what the safe range is for you. This may also be called your target range. It is important to tell your diabetes team and your cancer doctor or nurse if your blood sugar levels are not within your target range. They will give you advice on how to manage this.
Keeping within this range has been shown to:
- reduce the risk of infections and other side effects from cancer treatment
- improve overall well-being
- increase the effectiveness of your cancer treatment.
Short-term increases in blood sugar should not cause long-term complications. But it is important you are in regular contact with your diabetes team during your cancer treatment. This means they can support you as your diabetes management may change regularly.
Managing your blood sugar in the long term reduces your risk of complications such as damage to the heart, kidney, eyes and nerves. Some cancer treatments can also cause these problems, or make them worse. If you have diabetes, you will often need extra tests to check your health, and closer monitoring during your cancer treatment.
If you have lost weight before you start cancer treatment, the medication you take to lower your blood sugar may need to change. Your diabetes team can give you advice about this.
We have more information about monitoring and managing your blood sugar levels.
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:
- chemotherapy
- hormone therapy
- immunotherapy
- radiotherapy
- stem cell transplants
- steroids
- surgery
- targeted therapy.
Some treatments may be offered as a clinical trial. All clinical trials have rules about who can take part. These are called eligibility or inclusion criteria. If you have diabetes, you may not be able to take part in some cancer clinical trials. Your cancer specialist can tell you more about this.
Diabetes and side effects of cancer treatment
Cancer or its treatments can cause side effects that can affect your blood sugars. Some of the side effects include:
- feeling sick or being sick
- changes in appetite
- lack of activity
- diarrhoea.
You may also be more at risk of some side effects because of having diabetes. These include:
- infection
- slow wound healing.
It is important to check your blood sugar regularly during your treatment. This can help to reduce the risk of any problems. It is important to know the signs of high blood sugar (hyperglycaemia) and low blood sugar (hypoglycaemia) and how to manage them.
If you feel unwell, follow the sick day rules, and contact your cancer team and diabetes team for advice.We have more information on diabetes and the side effects of cancer treatment. Diabetes UK also have more information about managing diabetes and sick day rules.
Advanced cancer
Managing your diabetes can be more difficult if you have advanced cancer. Your healthcare team will discuss with you and your family any changes to your diabetes management as your health changes. Your diabetes team, cancer team and palliative care team can offer you advice and support.
We have more information about advanced cancer and diabetes.
Managing diabetes during Ramadan and Eid
If you are thinking about fasting during Ramadan, it is important to talk to your diabetes team beforehand. They can discuss how fasting could be a risk to your health and how to reduce risks. They can give you advice on how to manage your blood sugars during these times.
You will need to check your blood sugar level more often than you normally would during Ramadan and Eid. This is especially important if you are taking insulin or having cancer treatment that can affect your blood sugars.
Checking your blood sugar level does not break the fast. But you must break the fast if your blood sugars are too high or too low. If you are worried about this, talk to your religious leader before you start your fast.
Your diabetic team or GP can give you advice on the types of foods that can help to manage your blood sugars during Ramadan and Eid. Diabetes UK has more information about diabetes and Ramadan.
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.
About our information
This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer.
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References
Below is a sample of the sources used in our diabetes and cancer treatment information. If you would like more information about the sources we use, please contact us at informationproductionteam@macmillan.org.uk
Joint British Diabetes Societies for inpatient care (JBDS-IP). The management of glycaemic control in people with cancer. 2023.
Joharatnam-Hogan, N; Chambers, P; Dhatariya, K; and Board, R. The Joint BritishDiabetes Society for Inpatient Care (JBDS), UK Chemotherapy Board (UKCB). A guideline for the outpatient management of glycaemic control in people with cancer. Diabetes Medicine. 2022; 39.1-11. Available from: https://doi.org/10.1111/dme.14636 [accessed Oct 2022].
Shahid, R.; Shahid, A.; Duc, L; and Sunil, Y. Diabetes and Cancer, Risks, Challenges, Management and Outcomes. MDPI. 2021;13:1-21. Available from: www.ncbi.nlm.nih.gov/pmc/articles/PMC8616213 [accessed Oct 2022].
Date reviewed
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