Glucose exists in nature in several forms. Glucose often exists in plants as a simple monosaccharide sugar. Glucose also is a component of the disaccharide sugar, sucrose. In sucrose, glucose unites with fructose, also a monosaccharide simple sugar, to form sucrose. Glucose also is a component of lactose, a dairy sugar. In lactose, glucose unites with maltose, also a monosaccharide simple sugar, to form lactose. Finally, glucose also is a repeating component of various plant starches. Plant starches are polysaccharide sugars, long chains of simpler sugars that must be broken down to monosaccharide sugars before their absorption by the human intestine.
Sucrose, starches, and lactose must be digested to their monosaccharide sugar components before being absorbed by the human intestine. The monosaccharide sugar, glucose, is easily absorbed by the human intestine, and glucose travels easily throughout the entire blood stream, simply to be translocated by insulin into our various cells and tissues, where glucose serves as an immediate energy source. Insulin is necessary for glucose translocation into virtually all cells, and human insulin production is prompt and precise. Just enough insulin is secreted by the human pancreas to translocate circulating glucose into tissue cells. The pancreas possesses delicate glucose sensors that create a signal within the pancreas for insulin production and secretion, in proportion to the circulating glucose concentration and glucose load.
Insulin circulates in proportion to the absorbed glucose and promptly moves the glucose molecules from the blood stream into tissue cells throughout the human body. Glucose absorbed from a meal or a beverage normally leaves the bloodstream and enters tissues within 60-90 minutes.
The central problem in diabetes mellitus is that glucose movement from blood into various tissues is slow and delayed. It is slow and delayed for various reasons, but the consequence is that glucose molecules remain in the blood stream at higher than normal concentrations and for periods of time much longer than 60-90 minutes.
So what, one might ask? Well, the glucose molecule by its very nature is highly reactive with other molecules. That natural property is what makes it such an efficient energy source for living cells. But, if glucose circulates at higher concentrations for long periods of time, then the glucose molecules will react with blood vessel walls and with blood cells and blood proteins. These reactions are permanent, not reversible, and harmful. These reactions change the nature of the molecule or membrane that the glucose molecule reacts with. These reactions make vascular cell membranes stiff and thick. These reactions change hemoglobin in our red blood cells, and make the hemoglobin molecule heavy and less able to carry oxygen. These reactions change membrane properties of cells, so that special functions are altered.
Prolonged circulation of absorbed glucose is harmful. Any degree of elevation of blood glucose concentration is harmful.
Being aware of these facts compels prevention. The diabetic person must act knowledgeably to prevent his / her blood glucose from straying up above the normal glucose concentration range.
Otherwise, blood vessels throughout will be changed, thickened, narrowed, and permanently diseased. Other tissue membranes will be permanently diseased. These changes happen quickly and these changes accumulate. Eyes, kidneys, nerves, and blood vessels that serve muscles and skin and all our internal organs become the diseased victims. Any degree of elevated glucose concentration is thus harmful.