Prolonged exposure to high blood sugar can damage delicate nerve fibers, causing diabetic neuropathy. Why this happens isn't completely clear, but a combination of factors likely plays a role, including the complex interaction between nerves and blood vessels. High blood sugar interferes with the ability of the nerves to transmit signals. It also weakens the walls of the small blood vessels (capillaries) that supply the nerves with oxygen and nutrients.

Other factors that may contribute to diabetic neuropathy include:
-- Inflammation in the nerves caused by an autoimmune response. 
-- Genetic factors unrelated to diabetes that make some people more susceptible to nerve damage.
-- Smoking and alcohol abuse, which damage both nerves and blood vessels and significantly increase the risk of infections.

Risk factors
Anyone who has diabetes can develop neuropathy, but these factors make you more susceptible to nerve damage:
-- Poor blood sugar control. This is the greatest risk factor for every complication of diabetes, including nerve damage. 
-- Length of time you have diabetes. Your risk of diabetic neuropathy increases the longer you have diabetes.
-- Kidney disease. Diabetes can cause damage to the kidneys, which may increase the toxins in the blood and contribute to nerve damage.
-- Being overweight. Having a body mass index greater than 24 may increase your risk of developing diabetic neuropathy.
-- Smoking. Smoking narrows and hardens your arteries, reducing blood flow to your legs and feet.