Blood sugar (or glucose) is the main sugar found in the blood. It comes from the food you eat, and is the body's main source of energy. The bloodstream carries glucose (with the help of a hormone called Insulin) to all of the cells of the body in order for them to live. There is a range of healthy glucose/insulin levels, if they get too high or too low the body responds quickly with unpleasant symptoms. And if those levels stay out of range you might develop chronic conditions like Type 2 Diabetes and others. That's why taking care of blood sugar levels is so important.