Diabetes and side effects of cancer

Cancer and cancer treatment can cause different side effects. These side effects can affect your diabetes. You may feel sick, have diarrhoea or not manage to eat like you usually do.

It is important to contact to your diabetes team and your cancer team about managing your diabetes when you are having cancer treatment. Tell them if you are unwell. They will give you advice to help you manage your blood sugars. The advice is often called ‘sick day rules’. Sick day rules apply when you are feeling unwell for different reasons, not just feeling sick.

Sick day rules

• contact your diabetes team – they will give you advice on how to manage your blood sugar level
• stay hydrated
• keep eating and drinking
• check your blood sugar level regularly
• check for ketones.

You may be told to keep taking your diabetes medication even if you do not feel like eating. If you are unwell, there is some medication that you should not take as much of. And there are some you should stop taking. It is important to contact your diabetes team straight away if you are unwell.

If you take insulin, your dose may need to be changed when you are unwell. Talk to your diabetes team for more advice on how to manage your insulin doses when you are unwell.

We have more information about what to do when you are unwell. Diabetes UK also has more information about sick day rules.

When you have diabetes, it is important to be prepared. Follow the advice your diabetes team gives you. You might want to give this information to a friend or family member, so they can help you. Contact your diabetes team, who will help you if you have any queries or are unsure about what to do.

It is important that you know the symptoms of both high and low blood sugar levels, and how to manage them.

You will need to take extra care of your diabetes if you are feeling or being sick. Your diabetes team can give you advice to help you manage your blood sugars. They may give you sick day rules to follow.

If you check your blood sugar level at home, you will need to check it more often. This could be every 2 to 4 hours, including during the night. If you do not usually check it at home, it is important that you know the symptoms of a very high blood sugar level.

Try to keep eating and drinking as normal. It is important to keep hydrated, so have plenty of unsweetened drinks. If you cannot eat much, try snacks or drinks that contain carbohydrates to give you energy.

If you cannot eat without being sick, try to sip sugary drinks, such as fruit juice or non-diet cola or lemonade. You could also suck glucose tablets or sweets like jelly-beans. If you cannot drink without being sick, contact the hospital as soon as possible. It is important to prevent dehydration.

If your blood sugar level is high and you use insulin to control your diabetes, it is important to check your blood or urine for ketones and follow the advice on managing high blood sugar levels. You may be at risk of ketoacidosis (DKA). DKA is an emergency. We have more information about the symptoms of DKA and what to do if you think you have it. People with type 2 diabetes can develop hyperosmolar hyperglycaemic state (HHS).

Your diabetes medication

Keep taking your diabetes medication even if you do not feel like eating. But there are some medicines that you should not take as much of or stop taking altogether. Make sure you contact your diabetes team or a local pharmacist as soon as you are feeling ill. They will give you advice about what to do.

You should stop taking SGLT2i tablets if you become unwell or are in hospital for major surgery. If you take these tablets, you should check your blood sugar level. You should also check for ketones – in your blood rather than your urine, if possible. Contact your healthcare team straight away if you become unwell when taking SGLT2i tablets.

There are different types of SGLT2i tablets. Diabetes UK has a list of all the brand names. Taking these tablets when you are unwell could increase your risk of developing DKA. It is important to know the symptoms to look out for.

If you use insulin, you usually have it before eating. But if you are sick, you may not absorb enough food and your blood sugars may drop too low. If you are sick after eating, check your blood sugars and try to eat something to stop it getting too low.

If you are being sick, your insulin dose may need to be increased or decreased. The type of insulin you use may need to be change. When you are unwell, contact your diabetes team straight away for advice on how to manage your insulin.

If you are worried about coping with sickness, talk to your cancer doctor and your diabetes team. They can give you more advice.

Cancer and cancer treatments can affect your appetite. This may include losing your appetite or having a bigger appetite than usual.

Loss of appetite

During cancer treatment, you may lose your appetite. This could be because you feel sick, you are too tired to eat, or foods taste different. This usually does not last long.

If you have a small appetite, healthy eating for diabetes may not be appropriate. You may need to have high-energy, high-protein food and drinks during this time.

While you are not eating your normal diet, you will need to check your blood sugar level more often than normal. If you cannot eat enough, they may drop too low. This can lead to hypoglycaemia (a hypo). A good way to prevent a hypo is to eat regularly. If you cannot eat solid food, you could sip carbohydrate-containing drinks, such as whole milk, milky tea and coffees and fruit juice.

It is important to know the early signs of a hypo, so you can treat it quickly. Make sure your family and friends also know the symptoms, so they can help you. We have more information about the symptoms of a hypo and how to manage it.

While you have a poor appetite, your dose of insulin or your diabetes medicine may need to be changed to help prevent hypos. Your diabetes team or healthcare team will give you advice on this.

If you are struggling to eat, you can be referred to a dietitian for support and advice to help with your eating. There are meal replacement drinks that are available on prescription. Ask your doctor or dietitian whether they are appropriate for you. We have more information about eating problems and how to cope with them.

Tips to help improve your appetite

• Eat small amounts as often as possible. If your appetite is better at certain times of the day, try to plan your meals for then.
• If you change your mealtimes to help manage your blood sugar level, you may need to change when you take your diabetes medicines. Contact your healthcare team for advice about this.
• Keep snacks with you, such as bags of nuts, crisps or dried fruit. If these are hard to swallow, try creamy Greek yoghurt or fromage frais. If you have recently had surgery or radiotherapy for bowel cancer, you may need advice about the best foods for you. Talk about this with your specialist nurse or cancer doctor, or a dietitian.
• Try milk drinks made with whole milk, or savoury nourishing drinks. These can replace small meals and can be sipped slowly through the day. Your doctor or dietitian can prescribe special nutritional drinks that contain carbohydrates.
• Eat your meals slowly. Chew the food well and relax for a bit after each meal. We have more information about coping if you are struggling to eat because of a sore mouth.
• Have drinks after meals rather than before if you feel full easily.

Bigger appetite than normal

Some medicines, such as steroids, may make you want to eat much more than usual. It is important to try to eat healthy foods as much as possible. A balanced and healthy diet will help you manage your blood sugar level and avoid putting on too much weight.

Try to limit sugary foods and drinks, such as biscuits, chocolates, cakes and ice cream. These are high in calories and can raise blood sugar levels. Try to avoid drinking sugary drinks such as full sugar fizzy drinks and squashes. Instead choose ‘diet’, ‘zero’, or ‘no added sugar’ type drinks. Water is the best drink.

We have more information to help you cope with eating problems. Diabetes UK also has information and recipes to help you try to maintain a healthy weight.

The immune system protects the body from harmful bacteria and other organisms. Some types of cancer and cancer treatment can weaken your immune system and increase your risk of infection:

• Chemotherapy, radiotherapy, targeted therapy, immunotherapy and some types of cancer can reduce the number of white blood cells your body produces. White blood cells fight infection.
• Surgery may make you more at risk of infection. The skin acts as a barrier to infection, so any cut in the skin increases the risk of infection.

People with diabetes have more risk of an infection or a weaker immune system. This is usually if their blood sugar level is often too high.

Infections can raise your blood sugars to dangerously high levels. As part of the body’s way of fighting illness and infection, more sugar is released into the blood stream. This can happen even if you are not eating food or eating less than usual.

People who do not have diabetes produce more insulin to cope with the extra sugar. But if you have diabetes, your body cannot do this. The extra sugar will cause a high blood sugar level. This can make you feel more thirsty and pass more urine (pee), which can lead to dehydration.

Symptoms of an infection include:

• a high temperature
• suddenly feeling unwell, even with a normal temperature
• a painful, swollen or hot wound
• feeling shaky or shivering
• a sore throat
• a cough, especially if there is yellow or green phlegm
• diarrhoea
• needing to pass urine a lot, or pain when you pass urine.

If you develop any of these symptoms, tell your doctors straight away. They can give you antibiotics to fight the infection. They can also help you to manage your blood sugar level.

If you have an infection, you will need to check your blood sugar level more often. Talk to your diabetes team for advice on managing your blood sugar levels.

Tips to help you avoid infection

• Wash your hands regularly with soap and hot water, especially after going to the toilet or before preparing a meal.
• Have a shower or bath every day, and do not share towels with other people.
• Avoid people with sore throats, viruses, colds, flu, diarrhoea or vomiting, or infections such as chickenpox. If you have been around someone who has an infection, ask your cancer doctor or specialist nurse for advice.
• Stay away from crowded places as much as possible.
• Avoid using public swimming pools and jacuzzies. If you are doing sports or social activities, try to go when it is quiet.
• Be careful if you have pets or work with animals. If you can, try not to handle any animal waste, such as litter trays or manure.

We have more information about avoiding infection.