High Blood Sugar Levels - Hyperglycemia.

What are Normal Blood Sugar Levels?

Hyperglycemia (or Hyperglycaemia) is the medical term for high blood sugar. Normal blood sugar levels are between 4.0 to 7.0 mmol/L.

Hyperglycemia begins when blood sugar levels go above this range. All diabetic's including those on diet and exercise treatments can get this.

Ideally blood sugar levels should remain in the normal (non diabetic) range of 4 mmol/l to 7 mmol/l at all times.

Blood Sugar (Glucose) Reactions, Click for larger graph
Larger Graph (pop-up)

Note: For a UK to US unit conversion pop-up
see the What is Diabetes page.

The lower (pink) line shows a normal reaction to a meal. The upper (black) line show a Hyperglycemic reaction to a meal.

Its very common for diabetics on diet and exercise treatments as well as those on treatments by drugs & insulin to get some degree of hyperglycemia.

Occasional lapses in controlling blood sugar levels are hard to avoid. At minor levels above normal these are a low risk. Similarly even with the occasional high peak levels the increased risk is relatively minor.

Risks of diabetic complications do however rise with higher peak blood sugar levels. The higher these peaks rise and the longer that blood sugar levels are above normal the greater is that risk.

To minimise long term risk, good control is advised. Age too is important, diabetic complications are more common the longer you have had poorly controlled diabetes. Younger diabetics are advised to keep the tightest control.

Even if you are unable to get that full control, small reductions in peak blood sugar levels are worth aiming for.

Strictly to reduce the risk of diabetic complication, the best target figures are the normal range of 4 to 7 mmol/l. Other factors may apply to the target you have been given.

If you have been given a target higher than this and wish to know why, you need to consult with your GP or get professional medical advice. One possible answer for example could be if you are subject to frequent hypoglycemia (low blood sugar), in which case to avoid dangerously low levels, higher target levels may be suggested.

Typical Causes of High Blood Sugar Levels.

  • To much Carbohydrate.
  • To little Exercise.
  • Illness, Infections, Stress or Surgery.
  • To little Insulin or Drugs.
There may be no symptoms of high blood sugar especially at low levels. If they do appear however many diabetics will be familiar with the symptoms, which are unsurprisingly the same as those of a diabetic before diagnosis.

Over Corrections.

If you are not sure which way blood sugar levels are moving, take two readings 30 minutes to an hour apart to get a trend.

If quick acting insulin is used, it is quite easy to bounce from high to low blood sugar levels. Monitor the usual daily cycles to get an understanding of how they work and what effects you.

Exercising with High Blood Sugar Levels.

Exercising is a good way to encourage more efficient use of insulin for Type 2 diabetics and often can be useful in bringing down high blood sugar levels.

However if blood sugar levels go above 11 mmol/l only light exercising should be done and if levels are over 13.3 mmol/l no exercise should be done. This is because of the risk of ketosis at these high blood sugar levels.

Exercise while reducing blood sugar levels will also reduce insulin levels in the blood. When there is either insufficient insulin or insufficient glucose available the body turns to fat for fuel (see Ketosis).


Ketosis is the process of converting fat into energy. When blood sugar levels are high it can cause problems mainly in Type 1 diabetics. In these cases Ketosis may lead to the breath having a sickly fruity smell rather like pear drops or nail varnish.

While Ketosis is a normal process, at high levels the excess products of burning fat make the blood to acidic. Certain body functions stopping working at very high levels and the process can ultimately lead to coma and death.

Ketosis can be made worse by dehydration, so drink plenty of water or sugar free (no or low carbohydrate) fluids if you have high blood sugar levels, above 13.3 mmol/l.

Severe Hyperglycemia.

Very high levels above 33.3 mmol/l are extremely dangerous, symptoms include -
  • Dizziness when you rise
  • Difficulty breathing
  • Rapid weight loss
  • Increased drowsiness and/or confusion
  • Unconsciousness or coma

Important Note: Both Hyperglycemia and Hypoglycemia (low blood sugar) can cause unconsciousness and coma, giving the wrong treatment to someone in these states can lead to death.

Reducing High Blood Sugar Levels.

Occasional high blood sugar levels, exceeding the 7.0 mmol/L (or your individual) target are a relatively minor problem. Unless you are taking insulin there are few short term options for quickly reducing high blood sugar levels. Although exercise can help.

Frequent high blood sugar levels need medium to long term solutions and professional advice.

The solutions are usually a mixture of some or all of the following:-
  1. If you are over weight, lose weight.
  2. Use the Glycemic Index to choose foods that have less effect on your blood sugar levels. Take care though, aim to have a balanced and nutritious diet.
  3. Take regular exercise.
  4. See your GP or a medical professional. Consider changing or increasing your medication or moving on to insulin. If you regain good control you can always reduce medication.

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