Having an illness or infection can make it particularly hard to control blood sugar levels. A little knowledge of how illnesses affect diabetes can go a long way towards helping you through.

It’s hard to go a year without catching a cold, virus, flu or stomach bug so it pays to be prepared as to how to manage during periods of sickness.

How does illness affect diabetes?

During an illness or infection the body will release extra glucose into your blood stream in a bid to help combat the illness. In people without diabetes, this is an effective strategy as their pancreas will release extra insulin to cope with the extra blood glucose.

In people with diabetes, though, the release of glucose presents an unwanted extra difficulty in managing the rise in blood glucose levels – in addition to feeling less than 100%.

Illness and very high blood sugar levels

The NHS recommends that people with diabetes with a sugar level over 28 mmols/L should seek emergency advice from their healthcare team or, during out-of-hours times, contact NHS Direct on 0845 4647.

Coping with diabetes and illness

To keep a track of how much your sugar levels are rising, it’s recommended to test your blood more often than usual.

Test for ketones

If you have type 1 diabetes, it is advisable to follow up any high blood sugar readings with a test for ketones.

Keep hydrated

Keep yourself well hydrated.

High blood glucose levels can lead to dehydration so make sure you are regularly drinking fluids to stay hydrated.

Keep eating

It may be tempting to not eat whilst unwell but this could lead to more ketones as the body may need to break down fat to make fuel.

If eating is difficult, or if you are vomiting and cannot keep food down, it is advisable to have drinks with carbohydrate in instead of meals.

If you self-manage your insulin, be careful with how much insulin you take.


If your blood sugar rises without good reason and stays that way through the day, it could mean you’ve caught a cold or infection.

The body responds to infections by raising blood sugar, which can be problematic – as well as a surprise – for people with diabetes. It can be quite common for blood sugars to rise in this way even before the symptoms of illness come on.

If you have a blood glucose testing kit, then test your blood sugar more often than usual. Charity Diabetes UK advise people with type 1 diabetes to test for ketones if blood sugar level rise above 15 mmol/L to prevent a dangerous condition called ketoacidosis occurring.

It’s recommended to drink fluids regularly when ill to keep yourself hydrated.

If you take insulin it’s important you keep taking your insulin when ill. Diabetes UK say, if you’re having trouble keeping food down, it’s recommended to replace meals with drinks with carbohydrate in them, such as milk or sugary drinks, instead.

This will ensure you’re getting energy for your body. Some people will find they need to increase their insulin whilst they’re ill. If you’re unsure about anything, or struggling with your levels, contact your health team.

If blood sugars get too out of control and rise too high for too long, it can become dangerous.  Laboured breathing, dehydration, vomiting and loss of consciousness can be symptoms of dangerously high blood sugar levels. If these symptoms occur with illness, seek medical advice.

As the illness passes, you should find your normal levels settle again.

If you’ve increased your insulin whilst you were ill, you may find you start to get low levels and hypos -so be ready to change your doses back to what they were before the illness.

Keep taking your diabetes medication

This is important for all types of diabetes even if you are finding it difficult to eat.

If you are unsure about how much to dose, contact your health team. If the illness is becoming a struggle or your sugar or ketone levels are rising too high, it is also best to contact your healthcare team for advice.

If your blood glucose or ketone levels are rising too high, or you are vomiting it is best to contact your healthcare team for advice.

Diabetes, illness and ketones

People with type 1 diabetes are more susceptible to a dangerous condition called ketoacidosis (caused by very high sugar levels).

It is recommended to do a test for ketones if your blood sugar rises above 15 mmols/L.

This is usually a urine test but a few blood glucose meters allow for blood testing for ketones in a similar way as testing for sugar levels.

Managing blood sugar levels after illness

Blood glucose levels may take a few days to stabilise, even after you feel back to full health, so keep testing more often than usual until the blood sugar settles down.

Illness in children with diabetes

Whilst sugar levels have a tendency to rise during illness for most people with diabetes, children may find hypoglycemia occurs.

Regular testing is therefore strongly advised as is having a source of glucose for hypo treatment.

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