Blood sugar levels

Blood sugar level (also known as blood glucose level) is the amount of glucose (sugar) in the blood. It is also known as serum glucose level. The amount of glucose in the blood is expressed as millimoles per litre (mmol/l). Blood sugar levels are tightly regulated in the human body. Glucose, transported via the bloodstream, is the primary source of energy for the body's cells.

Though it is called "blood sugar," other sugars besides glucose are found in the blood, like fructose and galactose. However, only glucose levels are regulated via insulin and glucagon.

Normally, blood sugar levels stay within narrow limits throughout the day (4 to 8mmol/l). But they are higher after meals and usually lowest in the morning. If a person has diabetes, their blood sugar levels sometimes move outside these limits. Even with good control of diabetes, the blood sugar level will still at times drift outside this normal range.

How are blood sugar levels regulated by the body?

The levels of glucose in the blood are monitored by the cells in the pancreas. If the blood glucose level falls to dangerous levels (as in very heavy exercise or lack of food for extended periods), the pancreas releases glucagon, a hormone whose effects on liver cells act to increase blood glucose levels. They convert glycogen storage into glucose. The glucose is released into the bloodstream, increasing blood sugar levels.

When levels of blood sugar rise, whether as a result of glycogen conversion, or from digestion of a meal, a different hormone - insulin - is released, causing the liver to convert more glucose into glycogen, and to force muscle and fat tissue cells to take up glucose from the blood, thus decreasing blood sugar levels. Insulin also provides signals to several other body systems, and is the chief regulatory metabolic control in humans.

Why control blood sugar levels?

When very high levels of blood glucose are present for years, it leads to damage of the small blood vessels, which increases a diabetic's risk of developing late-stage diabetes complications like eye disease, kidney disease, nerve disease and cardiovascular diseases, such as heart attack, hypertension, heart failure, stroke and problems caused by poor circulation. Keeping the blood sugar levels stable significantly reduces the risk of these complications.

With Type 1 diabetes, these complications may start to appear 10 to 15 years after diagnosis. It's often less than 10 years after diagnosis of Type 2 diabetes, because this type of diabetes is often present for years before it is recognized.