Glucose is the body’s basic energy currency and is required by nearly every cell in the body to function healthily.
In fact, the brain, our most vital of organs, uses no other type of fuel and is the body’s heaviest glucose consumer, accounting for around 60% of our overall glucose metabolism at rest.
Glucose is delivered to your body’s cells by the blood that flows around them. Insulin, also carried in the blood, is the hormone responsible for persuading those cells to open their doors and let the glucose in.
Certain lifestyles, however, such as being inactive and overweight, can result in the body's cells starting to ignore insulin's knock on the door - a condition known as insulin resistance - leaving glucose levels to build up in the blood.
The key numbers
Blood glucose levels are very closely regulated and should stay within a relatively narrow range while you're awake of around 4.0 to 5.5 mmol/L (72-99 mg/dL).
Believe it or not, this range equates to less than one quarter of a teaspoon of glucose within your entire blood circulation - that’s how finely tuned your blood glucose regulation system needs to be.
Following a meal or sugary drink, the level will rise of course as the glucose is absorbed from the gut, typically to between 6.0 and 8.0 mmol/L (108 - 144 mg/dL) - but through the fine work of insulin, this should be brought back to within the normal range over the course of an hour or two.
This is why you’ll be advised to avoid food and drink for at least a few hours (usually up to 8-12 hours) when you have your blood glucose tested - to measure your baseline ‘fasting’ glucose level.
Diabetes and pre-diabetes
A fasting glucose of 7.0 mmol/L (126 mg/dL) or more is a diagnostic level for diabetes subject to further confirmation tests - but there is also a grey area between 5.5 and 7.0 mmol/L (99-126 mg/dL) where glucose levels are higher than ideal but not high enough to be classed as diabetes.
This is sometimes referred to as ‘pre-diabetes’ and reflects a relatively poor degree of blood glucose control. People with pre-diabetes values are at increased risk of progressing on to ‘full-blown’ diabetes unless they make the appropriate changes to their physical activity levels, diet and body weight to bring their glucose levels back under control.