What is the “right amount” of glucose in the blood? In fact, what is sugar doing in the blood in the first place, and why does the body need a complicated system of hormones to keep it in balance?

Glucose is the favored energy fuel for most cells of the body. It is carried throughout the body by the blood. A relatively small amount of sugar can supply the needs of the trillions of cells in the human body. All the blood of an average-sized adult man usually contains just about a teaspoon of glucose. But a person’s blood sugar level is not the same all the time. It goes up shortly after a meal, when foods from the digestive tract are passing into the bloodstream; and it goes down when a person hasn’t eaten for a long time. During your long night’s sleep, you don’t eat anything, so your blood sugar level is generally lowest just before breakfast. (This is called your fasting blood glucose level.)

In a healthy person, the swings in blood sugar level are not permitted to go very far. When sugar floods into the blood after a meal, the pancreas quickly secretes insulin, which helps the body cells get the sugar tucked away into storage. When a person has fasted or is starved, glucagon keeps the blood sugar level from falling too low. In a healthy person, the blood sugar level rarely rises above a concentration of 160 milligrams in each 100 milliliters of blood (which is expressed as 160 mg%), even after a meal, or falls below 60 mg%, even during a fast. The normal fasting blood sugar level ranges from 70 to 120 mg%, or about 80 mg% on the average.

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