The most common of the naturally occurring sugars. Glucose, also known as dextrose, corn sugar, and grape sugar, is found abundantly in such common foods as grapes, figs, other sweet fruits, and honey. The digestive tract also breaks down other food substances, such as starch, glycogen, sucrose, and lactose, into glucose. Glucose then enters the bloodstream through the intestinal wall. Excess glucose in the blood usually gets stored in the liver as glycogen.

It has long been known that excess glucose in the blood is the primary culprit behind diabetes complications, such as retinal disease, kidney disease, and nerve disease. For this reason, people with diabetes should regularly monitor their blood glucose levels and try to keep them within the normal range.