Key takeaways
- High blood sugar (hyperglycaemia) commonly causes extreme thirst, frequent urination, fatigue, blurred vision, and slow wound healing.
- Chronically elevated blood sugar raises the risk of type 2 diabetes, cardiovascular disease, kidney damage, and eye problems.
- Many people with type 2 diabetes initially have no obvious symptoms — the condition can go undiagnosed for years.
- Diet and lifestyle changes — fewer fast carbohydrates, more fibre, regular movement — help stabilise blood sugar.
- Always consult a doctor if you experience persistent symptoms. This article is informational only and does not replace medical advice.
Disclaimer: this article is for informational purposes only and does not replace medical advice. If you have symptoms, always consult a doctor or GP.
Blood sugar — also called blood glucose — is the concentration of glucose circulating in your bloodstream at any given moment. Your body regulates this precisely through insulin, a hormone produced by the pancreas. When that system is disrupted, blood sugar can rise too high. This is called hyperglycaemia.
Normal blood sugar levels
| Timing | Normal (mmol/l) | Too high (mmol/l) |
|---|---|---|
| Fasting (morning) | 4.0 – 5.6 | > 6.1 |
| 2 hours after a meal | < 7.8 | > 11.1 |
Symptoms of high blood sugar
Common symptoms:
- Extreme thirst (polydipsia): the body tries to dilute excess glucose through fluid intake
- Frequent, heavy urination (polyuria): the kidneys excrete excess glucose in the urine, drawing water along with it
- Fatigue and drowsiness: cells cannot absorb glucose efficiently without adequate insulin
- Blurred vision: high glucose concentrations temporarily affect the lens of the eye
- Headache: linked to dehydration and disrupted cellular function
- Slow wound healing: glucose impairs the function of white blood cells
- Dry mouth and skin
- Difficulty concentrating
Less well-known signs:
- A fruity or sweet smell on the breath (acetone odour) — this may indicate diabetic ketoacidosis, a serious complication
- Recurring infections, particularly fungal infections
Importantly, type 2 diabetes often presents with no obvious symptoms initially. An estimated proportion of people with diabetes go years without a diagnosis because symptoms develop gradually.
Causes of temporarily elevated blood sugar
Not every blood sugar spike indicates diabetes. The following factors can also cause temporary elevation:
- A meal high in fast carbohydrates or sugar
- Physical or emotional stress (cortisol raises blood sugar)
- Illness or infection
- Certain medications, including corticosteroids
- Insufficient sleep
Long-term consequences of chronically high blood sugar
When blood sugar remains persistently elevated, it can damage blood vessels and nerves. This raises the risk of:
- Type 2 diabetes: irreversible insulin resistance in which the body can no longer regulate blood glucose effectively
- Cardiovascular disease: damaged blood vessels increase the risk of heart attack and stroke
- Kidney damage (nephropathy): chronic overload causes damage to the kidneys
- Eye damage (retinopathy): small blood vessels in the retina are damaged, potentially leading to blindness
- Nerve damage (neuropathy): tingling, numbness, or pain in the hands and feet
What can you do yourself?
Dietary adjustments:
- Choose slow-releasing carbohydrates more often (wholegrains, legumes, vegetables) rather than fast ones (white bread, juice, sweets)
- Increase your fibre intake — fibre slows glucose absorption into the bloodstream
- Limit free sugars, as found in soft drinks, fruit juice, and sweet spreads
- Eat regular, moderate-sized meals to avoid large spikes
Lifestyle:
- Exercise regularly — even a 20-minute walk after eating measurably lowers blood sugar
- Get enough sleep: sleep deprivation disrupts insulin regulation
- Manage stress, or develop better coping strategies
Want to know how much sugar you consume daily? Read our article on how much sugar per day.
Track your food and calories
A conscious lifestyle starts with awareness. Our beginner's guide to calorie tracking shows you how to map your eating habits easily. Read also how to speed up your metabolism to better regulate blood sugar.
When to see a doctor
See your GP if you recognise several of the symptoms above, especially if they persist or worsen. A blood test (fasting glucose or HbA1c) will confirm your blood sugar status.
Seek urgent medical attention if you experience:
- Loss of consciousness, confusion, or extreme drowsiness
- A fruity breath odour combined with nausea and fatigue (possible ketoacidosis)
- You use insulin and are unsure how to treat a hyperglycaemic episode
High blood sugar is not always immediately noticeable, but the long-term consequences can be serious. Awareness of your diet, regular physical activity, and timely medical advice are the best protection. If in doubt, always consult a doctor.
Sources: Thuisarts.nl – High blood sugar in type 2 diabetes, UZ Leuven – Hyperglycaemia, SOHF – High blood sugar symptoms
