Exposure to excess amount of glucose in the blood, damages the delicate nerve fibers by interfering with the nerve cell transmission and also by weakening the walls of the blood capillaries that supply oxygen and nutrients to the nerves.
Hence, the damage caused to nerves (neuropathy) due to excess blood sugar levels is called as diabetic neuropathy. It mostly affects pain fibrils in the feet and lower legs, and rarely affects parts like abdomen, arm and the back.
Causes of Diabetes Neuropathy
It has been found that about 50% of the diabetics end up suffering from nerve damage. Even though the exact relation between the prolonged exposure of glucose and nerve damage is not yet known, researchers have found a combination of factors that disrupt the interaction between the blood vessels and nerves leading to nerve damage. The most common causes include:
This occurs mostly in patients suffering from Type I diabetes whose immune system becomes self-reactive and attacks its own body parts recognizing it as a foreign organism. This leads to inflammation in the nerves, which eventually leads to nerve damage.
Since nerves and blood vessels are inter-dependant on each other, vascular abnormalities like capillary membrane thickening, endothelial hyperplasia and hypoxia can cause neuronal dysfunction, the most prominent among diabetic patients being neuronal ischemia (insufficient blood supply to neurons).
Damage to Biochemical Pathways
Glucose is a very reactive compound and when present in excess, can easily react with tissues in the body. Cells of the kidney, retina and nervous system do not require insulin for the uptake of glucose unlike the other cells of the body.
This allows free interchange of glucose which in a hyperglycemic condition activates the polyol or sorbitol pathway that is responsible for decreasing the levels of glutathione in the body. Glutathione being a powerful antioxidant, when depleted leads to the increase in the levels of powerful reactive oxygen radicals that are responsible for nerve damage.
Covalent Bonding With Proteins
Elevated levels of glucose interact with certain glycosylated proteins and alter their function and structure. This phenomenon termed as non-enzymatic glycosylation leads to the accumulation ofreactive oxygen species in the blood causing diabetic neuropathy and many other diabetes-related complications.
Alcohol and Cigarette Smoking
Nicotine found in tobacco constricts blood vessels causing high blood pressure and restriction of the blood flow through the vessels. This damage to the blood vessels does not allow them to adequately supply oxygen and nutrients to the nerves. Alcohol (even light drinking) in diabeticshas shown to cause nerve damage increasing the pain, numbness, tingling or burning sensation in the feet or in any other the body part that gets affected. Besides alcohol can also increase the amount of triglycerides in the blood, thereby resisting the blood flow from the capillaries to the nerves.
Other causes include hypertension, hypercholestrerolemia, increase in intracellular Protein Kinase C levels that decrease nerve conduction velocity, an age above 40, obesity and genetic predisposition that makes certain individuals susceptible to nerve damage. Many cuts and sores on the feet could go unnoticed as a result of loss of sensation of pain due to nerve damage in the feet. Hence, improper foot care can aggravate the symptoms of diabetic neuropathy leading to foot ulcers and leg amputations.