What makes glucose levels rise and fall?

When you have diabetes it helps to understand what might make your glucose rise or fall so you can take steps to stay in target range.

When you eat any type of carbohydrate – such as pasta, fruit, bread or sugar –  your body breaks it down into glucose. Glucose is absorbed into the bloodstream and insulin helps remove it from your blood into your cells to be used for energy. Without diabetes, the body usually makes just the right amount of insulin to match the food and activity, and glucose levels naturally rise and fall in response.1

When diabetes develops, the process is disrupted, either because the body stops producing insulin altogether (Type 1 diabetes) or because the insulin it produces becomes less effective (Type 2 diabetes).

The main aim of treating diabetes is to keep your glucose levels within a target range you agree with your diabetes care team. This is to prevent short-term and long-term health problems that can occur when glucose falls too low (hypoglycaemia) or too high (hyperglycaemia).2

For illustrative purposes only, not real patient

What can make my glucose rise?2

  • eating a bigger portion of carbohydrates than usual
  • being less active than usual
  • reduced dose of insulin or diabetes medications
  • taking certain medications
  • having an infection, virus or surgery
  • changes in hormone levels, such as during periods or pregnancy
  • stress
  • dehydration

What can make my glucose fall?2

  • eating a smaller portion of carbohydrates than usual or missing a meal or snack
  • taking too much insulin or diabetes medication
  • being more active than usual
  • taking certain medications
  • drinking alcohol

How can I track my glucose levels?

If your diabetes is treated with insulin or medications that lower glucose or stimulate insulin production, your care team will advise you to test your glucose regularly. Regular testing helps you learn how your glucose levels respond to different foods, medication and activity, so you can spot patterns and trends. This can help you fine-tune your diabetes routine to stay well and prevent your glucose levels falling too low or rising too high.

What is hypoglycaemia?

Hypoglycaemia (also called a hypo) means your glucose level is low, usually below 4mmol/L. 6 When this happens there may not be enough glucose to provide your body with energy. Hypos are hard to avoid altogether, but they shouldn’t happen often, get worse or become severe enough for you to pass out. Having more than three or four hypos a week is a sign your diabetes routine isn’t working, so talk to your care team.3

How do I know I’m having a hypo?

Symptoms of a hypo usually occur when glucose falls to below 4mmol/L. Typical early warning signs that your glucose level is going low include:3

  • trembling
  • sweating
  • feeling hungry or tired
  • blurred vision

More severe symptoms include confusion or difficulty concentrating, and it’s even possible to lose consciousness.4 Some people though don’t have any warning signs, or become less ‘hypo-aware’ over time.4

For illustrative purposes only, not real patient

Can I have a hypo while I’m asleep?

You can have a hypo when you are asleep, which can cause excess sweating, disturbed sleep and feeling tired when you wake up.5 The easiest way to find out is to test your glucose level during the night. If you suspect or discover you’re having night-time hypos, it’s important to discuss how to prevent them with your diabetes care team.

How do I treat a hypo?

Hypoglycaemia can happen suddenly and it can usually be treated quickly and easily by taking a small amount of glucose, such as:5

  • a small glass of sugary (non-diet) drink
  • 3 glucose or dextrose tablets
  • a small carton of pure fruit juice

Have this fast-acting glucose snack even if you are about to eat a meal.

After 15-20 minutes, re-test your glucose levels; if you are still below 4mmol/L have another portion of high-glucose food or drink.5

Once your glucose level is above 4mmol/L, you could have a longer-acting starchy carbohydrate food, such as a sandwich, to keep your glucose from dropping again.11

What is hyperglycaemia?

Hyperglycaemia happens when your glucose level goes too high. The symptoms are similar to the symptoms of untreated or undiagnosed diabetes and include:7

  • feeling thirsty
  • urinating often, especially at night
  • feeling tired
  • over time there may be other symptoms including weight loss and blurred vision

If your blood glucose is over 13.9mmol/L and does not drop over the next two hours, or if you are ill, you may be at risk of developing diabetic ketoacidosis, which is a medical emergency. Test your blood for ketones and contact your diabetes care team.8

How do I treat hyperglycaemia?

If your glucose level is too high, it’s important to bring it down within your target range, but without lowering it so much that you have a hypo. This may mean something simple like taking some exercise, or taking a little more insulin.7 If your glucose level is persistently too high it’s a sign your diabetes routine isn’t working, so talk to your diabetes care team.7  

What do I need to know about insulin?

Everyone who has Type 1 diabetes, and some people with Type 2 diabetes, need insulin to manage their condition. Most people inject insulin using a pen with a fine needle, or if you have Type 1 diabetes you may be offered an insulin pump.9 All insulin supplies used to be sourced from animals such as cows or pigs, but synthetic insulins that mimic human insulin were developed in the 1980s and most people now use these.10  Some people who found it difficult to switch to synthetic insulins use older, animal-based products.

Different types of insulin serve different purposes and many people use more than one type in a ‘basal-bolus’ routine. This means taking a long-acting insulin to manage glucose levels through the day and night, and a faster-acting dose at mealtimes.10

It can take time to get insulin timing and doses right. Testing your glucose regularly and working with your diabetes care team can help you find a routine that works around your lifestyle.

The main types of insulin are:

Rapid-acting insulin

Rapid-acting insulins take effect between 10 and 30 minutes after injecting. They’re usually injected before eating a carbohydrate meal and a dose is effective for up to five hours. 10

Short-acting insulin

Short-acting insulins are similar to rapid-acting types but work a little more slowly. They’re also used around mealtimes as ‘bolus’ doses.9

Mixed insulin
Taking a single dose of mixed short- and long-acting insulins means fewer injections each day, but can restrict the timing of meals and exercise.10

Intermediate-acting insulin

Intermediate-acting insulin is taken as a ‘basal’ or background dose, usually once or twice a day.9

Long-acting insulin

Long-acting insulin is usually injected once a day to provide background insulin for up to 24 hours. Long-acting insulin has been shown to reduce the risk of hypos compared to other types.9

It’s important not to take more than your prescribed dose of insulin as this can cause a dangerous hypo. If you think you’ve taken too much insulin by accident, eat some fast-acting glucose and seek medical help.9


1. National Institute of Diabetes and Digestive and Kidney Diseases 2014, Carbohydrate counting and diabetes, accessed 29 March 2019, https://www.niddk.nih.gov/health-information/diabetes/overview/diet-eating-physical-activity/carbohydrate-counting.

2. American Diabetes Association 2015, Factors affecting blood glucose, accessed 29 March 2019, http://www.diabetes.org/living-with-diabetes/treatment-and-care/blood-glucose-control/factors-affecting-blood-glucose.html.

3. NHS 2017, Hypoglycaemia, accessed 29 March 2019, https://www.nhs.uk/conditions/low-blood-sugar-hypoglycaemia/.

4. InDependent Diabetes Trust 2019, Loss of warnings or hypoglycaemia unawareness, accessed 29 March 2019, https://www.iddt.org/related-health-issues/what-is-hypoglycaemia/loss-of-warnings-or-hypoglycaemia-unawareness.

5. NHS 2018, Type 1 diabetes. Hypoglycaemia (hypos), accessed 29 March 2019, https://www.nhs.uk/conditions/type-1-diabetes/hypoglycaemia-hypos/.

6. JDRF 2019, Managing Type 1 diabetes. Hypos, accessed 29 March 2019, https://jdrf.org.uk/information-support/managing-type-1-diabetes-3/hypos/.

7. NHS 2018, Hyperglycaemia, accessed 29 March 2019, https://www.nhs.uk/conditions/high-blood-sugar-hyperglycaemia/.

8. Gloucestershire Hospitals NHS Foundation Trust 2017, Testing for ketones, accessed 29 March 2019, https://www.gloshospitals.nhs.uk/.../166/Testing_for_ketones_GHPI1140_09_17.pdf

9. Diabetes UK 2019, Treating your diabetes. Insulin, accessed 29 March 2019, https://www.diabetes.org.uk/guide-to-diabetes/managing-your-diabetes/treating-your-diabetes/insulin#Types/.

10. JDRF 2019, Insulin, accessed 29 March 2019, https://jdrf.org.uk/information-support/treatments-technologies/insulin/.

11. Diabetes UK 2019, Guide to diabetes. Having a Hypo, accessed 8 May 2019, https://www.diabetes.org.uk/Guide-to-diabetes/Complications/Hypos/Having-a-hypo/.



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