Blood sugar levels are determined by the amount of glucose in the blood stream. Energy is provided to the body from foods high in carbohydrates which, via the digestive process, are converted to glucose, a type of sugar. Normal amounts of sugar in the blood are essential for proper health, though dangerously low or high levels of blood sugar can be detrimental.
Blood sugar is measured by blood glucose tests. Normal levels are considered to be those between 60 and 130 mg/dl (milligrams of glucose per decilitre of blood).
A high blood sugar level, or hyperglycaemia, is dangerous in that it can lead to stroke, eye and nerve disorders, the need to urinate frequently, and kidney or heart disease. Dangerously high glucose levels are those over 200 mg/dl. For diabetics, danger levels begin at 180 mg/dL.
Danger also exists when blood glucose levels are below 60 mg/dl. This condition is called hypoglycaemia, and symptoms include fatigue, insomnia, cold hands and feet, blurred vision, heart palpitations, confusion, depression and a craving for sweets.
Blood sugar levels are normally elevated after meals, therefore glucose measurements are taken after fasting eight or more hours before the test, called Fasting Blood Sugar (FBS), or if the test is taken soon after a meal, post-prandial.
Diabetes is a disease in which blood sugar levels are over 200 mg/dl (FBS). Although less of a concern, glucose measurements of 100 to 125 mg/dl (FBS) or 140 to 199 mg/dl (post-prandial) are considered pre-diabetic levels.
Hypoglycaemia has been linked to dementia in elderly diabetic patients. It is also listed as a cause of mental retardation in children who have had prolonged episodes of dangerously low blood sugar levels.