High blood sugar (hyperglycaemia) is a condition where there is too much glucose in your blood stream. It is normal for blood glucose levels to go up and down during the course of a day, for example after you eat. However, if your blood glucose levels stay abnormally high over a long period of time it can lead to serious health problems including damage to your eyes, nerves, blood vessels and organs.
High blood sugar usually only occurs in people with diabetes. People with diabetes cannot control their blood glucose levels, and without careful management through lifestyle, diet and medication people with diabetes will have dangerously high blood glucose levels.
What is the cause of high blood sugar?
In healthy people, blood glucose levels are prevented from getting too high by the release of insulin from the pancreas. Insulin is released when you eat, and causes glucose digested from food to be removed from the blood stream and absorbed into the cells of your body. People with type 1 diabetes are born unable to produce insulin and people with type 2 diabetes have developed a reduced ability to produce and / or respond to insulin in a normal way (known as insulin resistance).
In terms of blood glucose levels, type 2 diabetes is defined based on the results of blood glucose measurements.
Blood glucose higher than or equal to 126 milligrams per decilitre of blood (mg/dL) after an 8-hour fast – usually measured first thing in the morning.
Non-fasting glucose level greater than or equal to 200 mg/dL combined with symptoms of diabetes.
A measurement called ‘HbA1C’ greater than or equal to 6.5%. This provides a measurement of how high your blood glucose has been over a period of around 3 months and gives an idea of your average blood glucose measurement over this time period.
What are the risk factors and symptoms of high blood sugar?
The main risk factors for type 2 diabetes are being over 45 years of age, family history of type 2 diabetes, being of south Asian, Chinese, African Caribbean or black African origin, obesity and an inactive lifestyle.
Symptoms of type 2 diabetes include needing to urinate more than normal, particularly at night, feeling thirsty all the time, feeling very tired, losing weight without trying to, blurry vision, cuts or wounds taking longer to heal than normal, itching around your genitals, or repeatedly getting thrush infections.
How is high blood sugar treated?
High blood sugar is treated with a combination of lifestyle and diet changes and medication. Important lifestyle changes include daily exercise and eating a balanced diet with minimized sugar, fat and salt.
You should always talk to your doctor before beginning an exercise programme or radically changing your diet.
References
DeFronzo RA. Med Clin North Am. 2004 Jul;88(4):787-835, ix.
International Diabetes Federation. IDF Diabetes Atlas, 9th edn. Brussels, Belgium: 2019. Available at: http://www.diabetesatlas.org.