Control of blood glucose levels is essential for those suffering from diabetes If blood glucose levels are too low, hypoglycemia strikes. Symptoms progress from dizziness and confusion to convulsions, coma, and death. The low end of the normal range is usually given as 70 mg/dl. The exact levels at which the hypoglycemia symptoms set in vary from patient to patient, and even for a single patient these levels can vary from time to time. Depending on food intake and insulin injected, a person could go from high blood glucose levels (greater than 130 mg/dl) to death while they sleep. Thus, control of blood glucose levels is essential to maintaining health, and the primary goal of glucose control is to, at all costs, keep glucose levels above the deadly low levels.
On the other hand, if blood glucose levels are too high, no immediate effects are visible. It is tempting to then keep blood glucose levels higher than normal, to avoid the threat of death from low blood glucose levels. However, long term (over years) effects occur due to high levels of blood glucose, these effects can include damage to nerves and blood vessels. This damage can lead to blindness, kidney problems, and heart disease.