Diabetes is a disease in which the level of glucose, a type of sugar, in the blood is too high. Over time, high levels of blood glucose can cause serious damage to organs such as the eyes, kidneys and heart by damaging the blood vessels that supply them. This damage is not seen at the onset of diabetes, however. Most of the early symptoms of untreated diabetes are caused by the osmotic effects of the high glucose levels.
Increased Urination and Thirst
Normally, the kidneys remove almost all of the glucose from urine before sending it to be stored in the bladder. When blood glucose levels are elevated, however, they overwhelm the ability of the kidneys to move glucose and a significant amount of it ends up in the urine. The increased concentration of glucose in the urine brings in additional water by osmosis, which increases the volume of urine in the bladder. The increased urine volume leads to more frequent urination, and this increased loss of water leads to increased thirst.
Unexplained Weight Loss
The loss of glucose through the urine in uncontrolled diabetes can account for as much as 500 to 1,000 calories a day, roughly equivalent to running five to ten miles. In a person whose weight has been stable, this extra consumption of calories can result in the loss of up to two pounds a week. The weight loss seen in uncontrolled diabetes is not healthy, however, since much of it comes from the breakdown of muscle protein rather than the mobilization of fat from adipose tissue.
Blurry Vision
The lenses of the eyes are mostly fluid, and the level of glucose in this fluid is determined mostly by the level of glucose in the blood. When the glucose in the lens fluid rises in response to increased glucose in the blood, more water enters the lenses through osmosis. This extra water distorts the optical properties of the lenses, leading to blurry vision. Unlike the long-term eye damage seen in diabetes due to damaged blood vessels, the blurry vision experienced at the onset of uncontrolled diabetes will clear up once blood glucose is under control.
References
- "Harrison's Principles of Internal Medicine"; Dennis L. Kasper
- The Mayo Clinic: Diabetes
