Blood sugar levels

What is blood sugar?

10 Jun 2023

You’ve probably experienced blood sugar highs and lows but do you really know what’s causing them? Find out all about your blood glucose, and how to stay in control

Written by Colleen Shannon on February 25, 2019 Reviewed by Dr Sarah Schenker on March 6, 2019

If your energy and concentration levels keep crashing, blood sugar fluctuations could be to blame – and you don’t need to have diabetes to experience those highs and lows. Check out our guide to blood sugar (for those without diabetes) and how you can help rebalance yours.

What is blood sugar?

Blood sugar, also known as glucose, is the most important type of sugar found in the blood.1 We get glucose by breaking down carbohydrates found in our food and drink.2 Glucose is the main source of energy for all the cells in your body. Your brain, which uses 20% of your energy, needs a constant supply of glucose from your bloodstream to function properly.3

How your body controls blood sugar

If you’re healthy – and don’t have diabetes – your blood sugar naturally goes up and down during the day and night. For example, you’ll usually experience a temporary blood sugar spike after eating a meal.

However, our bodies are usually pretty good at controlling these peaks and trough thanks to the pancreas, the ‘control centre’ for blood glucose.4 Your pancreas produces two hormones that work in a finely-tuned balance to keep blood sugar levels steady:

  • insulin – large amounts are released when your blood sugar levels go up, for example right after a meal, to allow your cells to take up and use glucose in the bloodstream5,6

  • glucagon – this is needed when your blood sugar levels drop; it stimulates cells, mainly in the liver, to release stored glucose into your bloodstream to boost energy levels7,8

What causes low blood sugar (hypoglycaemia)?

For many of us, it’s simply a long gap between meals or fasting. Drinking too much alcohol or pregnancy can also cause symptoms of low blood sugar, including:9
  • hunger
  • tiredness
  • shakiness
  • irritability
Another cause of low blood sugar in people without diabetes is reactive hypoglycaemia, which is most likely caused by eating a large, carbohydrate-heavy meal. The meal can trigger an overproduction of insulin, which then forces a drop in blood sugar. It’s more common in people who are overweight.10

High blood sugar (hyperglycaemia)

You can experience a rapid rise in blood sugar if you eat foods that score high on the glycaemic index, like white bread, cakes and biscuits: these are broken down faster into glucose than low-GI foods, leading to a spike in blood sugar.11 However, people without diabetes are unlikely to experience these symptoms because the pancreas normally steps in to reduce blood sugar levels.12 If you have been experiencing the following symptoms of high blood sugar, it’s important to see your GP to test for diabetes:13
  • unusual thirstiness
  • frequent urination
  • tiredness
  • blurred vision
  • weight loss without trying
  • tummy ache
  • feeling nauseous, or vomiting
  • fruity-smelling breath

What can go wrong with controlling blood sugar?

Your pancreas cannot regulate blood sugar levels properly when you have type 1 or type 2 diabetes, or gestational diabetes.14 Very rarely, blood sugar regulation can also be affected by:15,16,17
  • some medications, including anti-malarial quinine, beta blockers or steroids
  • certain health conditions, for example hepatitis, anorexia or bulimia, kidney disorders
  • hormone deficiencies

How to keep your blood sugar balanced

It’s important to keep your blood glucose steady, as both higher than normal levels and reactive hypoglycaemia are linked to an increased risk of developing type 2 diabetes.18,19

These tips can help you stay in control:

  • eat foods that score low on the glycaemic index – low GI foods such as wholegrains, most fruits, pulses and vegetables are broken down more slowly into glucose for a gradual energy release20

  • take regular exercise – it has been shown to improve your body’s regulation of blood sugar and insulin sensitivity21

  • avoid eating big meals – try eating smaller meals balanced with snacks

Scientists have also looked at certain herbs and supplements that could maintain healthy blood glucose levels. These include:

  • cinnamon – a 2015 Portuguese study found drinking cinnamon tea could lower post-meal blood glucose levels in people without diabetes,22 but a 2019 review in Nutrition Today reported mixed results and suggested more research is needed23

  • magnesium – in a 2016 report in the European Journal of Clinical Nutrition, magnesium helped reduce blood glucose levels in people considered at risk of developing diabetes24

If you have diabetes and have questions about controlling your blood glucose, ask your GP for advice.

Shop Vitamins & Supplements Advice is for information only and should not replace medical care. Please check with your GP before trying any remedies.


1. MedlinePlus. Blood sugar 2. British Dietetic Association. Food fact sheet: Food and mood

3. As above

4. Freckmann G, et al. Continuous Glucose Profiles in Healthy Subjects under Everyday Life Conditions and after Different Meals 5. The Endocrine Society. What is insulin? 6. Society for Endocrinology. Insulin 7. Endocrine Society. What is glucagon? 8. Society for Endocrinology. Glucagon 9. NHS Choices. Low blood sugar (hypoglycaemia) 10. Chaunie Brusie. Healthline. Can You Have Hypoglycemia Without Having Diabetes? 11. Harvard T.H. Chan School of Public Health. Carbohydrates and Blood Sugar 12. Amy Hess-Fischl. Endocrineweb. Hyperglycemia: When Your Blood Glucose Level Goes Too High 13. NHS Choices. Hyperglycaemia 14. Pancreas and Diabetes 15. Mayo Clinic. Hypoglycemia – Symptoms and causes

16. As Source 9
17. As Source 12

18. Hemmingsen B, et al. Diet, physical activity or both for prevention or delay of type 2 diabetes mellitus and its associated complications in people at increased risk of developing type 2 diabetes mellitus 19. Kathleen Jade. University Health News. Diabetes: Prediabetes Warning: Hypoglycemia vs Diabetes 20. NHS. What is the glycaemic index (GI)? 21. Harvard Medical School. Healthy Mind, Healthy Body: Benefits of Exercise 22. Bernardo MA, et al. Effect of Cinnamon Tea on Postprandial Glucose Concentration 23. Singletary K. Cinnamon: Update of Potential Health Benefits 24. Veronese N, et al. Effect of magnesium supplementation on glucose metabolism in people with or at risk of diabetes: a systematic review and meta-analysis of double-blind randomized controlled trials

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