Diabetes and side effects of cancer

Cancer or its treatments can sometimes make you feel sick (nausea) or be sick (vomit).

Being sick can be a problem when you have diabetes. Because you may not be able to eat or drink, you could become dehydrated. Your blood sugar level can get very high (hyperglycaemia – a hyper) if you are dehydrated. This can be more serious for people with diabetes.

Before you start any cancer treatment, talk to your cancer doctor or specialist nurse. Explain that you have diabetes and that you need to prevent sickness as much as possible. Ask your diabetes team for advice about managing sickness. They can tell you how to manage your diabetes when you are ill. These are known as the 'sick-day rules'. It is helpful for family or friends to know how to manage things too.

Tell your cancer doctor or specialist nurse straight away if you are feeling sick and cannot eat or drink anything.

Controlling your blood sugar when feeling or being sick

You will need to take extra care of your diabetes if you are feeling or being sick.

You will need to check your blood sugar more often. This could be every 2 to 4 hours, including during the night.

You should also be aware of the symptoms of a very high blood sugar level. These symptoms include:

• passing a lot of urine, especially at night
• being very thirsty
• headaches
• being very tired.

If your blood sugar is very high and you use insulin to control your diabetes, you may need to check your blood or urine for ketones. Ketones are chemicals that can sometimes build up in the body when there is a severe lack of insulin. They are toxic to the body and large amounts can be very serious. If you have ketones in your blood or urine, you should contact your diabetes team for advice straight away.

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

If you cannot eat without being sick, it is okay to sip sugary drinks, such as fruit juice or non-diet cola or lemonade. You could also suck on glucose tablets or sweets like jelly beans. Contact your doctor as soon as possible if you are vomiting and cannot keep any fluids down.

Your diabetes medicines

Try to keep taking your diabetes medicines as normal.

If you use tablets to manage your diabetes, you may need to stop taking them while you are being sick. Your diabetes team can give you more advice.

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

It is a good idea to have a fast-acting carbohydrate nearby, such as glucose tablets, sweets or fruit juice. You should try to follow this with a snack containing slower-acting carbohydrates, such as a slice of toast or a couple of digestive biscuits. The fast-acting carbohydrates will quickly increase your blood sugar level. The slow-acting carbohydrates will stop it dropping again.

If you cannot eat solid foods, you could have a milky drink. Your doctor can also prescribe special nourishing drinks containing carbohydrates.

If you are being sick, you may need to change the dose of your insulin or change the type of insulin you use. You should not stop taking it. Your diabetes specialist can give you advice.

Tips to help with eating

• Try to stick to what you usually eat. Try to eat the same amount of carbohydrates as normal. But if this is difficult, it is okay to eat foods you would not normally eat.
• You may need to eat little and often.
• If feeling sick is putting you off food or you cannot eat without being sick, replace meals with snacks or drinks that contain carbohydrates. These could include glucose tablets, fruit juice or non-diet fizzy drinks. Fizzy drinks that have gone flat may be easier to drink.
• Try to keep drinking even if you cannot eat. Aim to drink a cup of fluid every hour.

We also have general information about nausea and vomiting, including more tips to help with eating.

If you cannot drink without being sick, contact the hospital as soon as possible. It is important to prevent dehydration.

You should talk to your diabetes team if you are worried about coping with sickness. They will be able to give you more advice.

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 diabetes and cannot eat enough, your blood sugar may drop too low. This can lead to hypoglycaemia (a hypo). 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.

Symptoms of a hypo include:

• sweating
• feeling anxious and irritable
• feeling extremely tired (fatigue)
• feeling weak and shaky
• looking pale
• being hungry
• having a faster heart rate than normal.

A good way to prevent a hypo is to eat regularly. If you cannot eat solid food, you could sip sugary drinks.

While you are not eating your normal diet, you will need to check your blood sugar more often than normal. If your blood sugar level starts to get lower or you develop symptoms of a hypo, try eating or drinking a fast-acting carbohydrate. This could be glucose tablets, sweets or fruit juice. Try to follow this with a snack containing slower-acting carbohydrates, such as a slice of toast or a couple of digestive biscuits. The fast-acting carbohydrates will increase your blood sugar level. And the slow-acting carbohydrates will stop them dropping again.

While you have a poor appetite, you may need to change your dose of insulin or tablets to help prevent hypos.

Your diabetes team can give you advice about preventing hypos and how to manage them if they happen.

Tips to help improve your appetite

• Eat small amounts as often as possible. If you find your appetite is better at certain times of the day, try to plan your meals for then. You may need to change when you take your diabetes medicines.
• Keep snacks with you. Bags of nuts, crisps or dried fruit, or a bowl of grated cheese, are light and tasty. If these are hard to swallow, try 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 sweet or savoury nourishing drinks. These can replace small meals and can be sipped slowly through the day.
• Eat your meals slowly. Chew the food well and relax for a bit after each meal.

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. Try to avoid foods that are high in carbohydrates and sugar, such as biscuits and sweets.

A balanced and healthy diet will help you avoid putting on too much weight. Having a healthy weight is important for managing your blood sugar levels.

We have more information to help you cope with eating problems.

Diabetes UK has more 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 its treatment can weaken your immune system and increase your risk of infection.

People with diabetes may be more at risk of an infection or a weaker immune system. This is usually if their blood sugar level is often too high. Your diabetes team can give you advice if you have problems keeping your blood sugar level under control.

The body tries to fight infection by releasing extra sugar into the blood. If you do not have diabetes, the pancreas will make more insulin to cope with the extra sugar. But if you have diabetes, the extra sugar will cause high blood sugar levels (a hyper). This can make you feel more thirsty and pass more urine (pee), which can lead to dehydration.

If you develop any symptoms of an infection, it is important to talk to your doctors as soon as possible. They can give you antibiotics to fight the infection. They can also help you to control your blood sugar level.

If you have an infection, you will need to check your blood sugar level more often. If you usually control your diabetes with diet, you may need to start taking medicines. If you already take medicines, you may need to change the dose. Talk to your diabetes team if you have an infection and your blood sugar level is high.