Diabetes affects the body's ability to produce or use insulin, the hormone that allows cells to take up sugar from the bloodstream and use it for energy. When insulin is insufficient or ineffective, blood sugar rises above the normal range and stays there.
The complications that follow are, to a striking degree, vascular. Persistently elevated blood glucose damages blood vessels — both the large arteries feeding the heart, brain and legs, and the small vessels supplying the eyes, kidneys and nerves. It is reasonable to think of diabetes as a disease of the blood vessels that happens to be diagnosed with a blood sugar test.
How high blood sugar damages arteries
The first step is endothelial dysfunction. Elevated glucose injures the lining of the blood vessel, impairing its ability to dilate normally and making it inflamed and more permeable to circulating cholesterol.
That sets up atherosclerosis, in which fatty deposits accumulate within the artery wall and progressively narrow it. In people with diabetes, atherosclerosis tends to appear earlier, progress faster, and affect longer segments and smaller vessels — particularly the arteries below the knee, which are technically more demanding to treat.
Hypertension frequently accompanies diabetes and compounds the damage, adding mechanical stress to vessels already biologically injured. The combination of high sugar, high pressure and high cholesterol is the reason cardiovascular disease affects such a large proportion of people with diabetes over the age of sixty-five.
Why diabetic vascular disease is especially dangerous in the legs
Diabetes causes peripheral neuropathy alongside vascular disease, and the two together are what make diabetic foot problems so serious. Neuropathy blunts sensation, so a blister, a cut or a pressure sore may not be felt at all. Poor arterial circulation then prevents that wound from healing. An injury the patient never noticed becomes an ulcer, and an ulcer with inadequate blood supply becomes an infection.
This is why foot inspection is not a trivial recommendation for people with diabetes. It substitutes deliberate looking for the pain signal that neuropathy has removed.
Diagnosis
Diabetes is diagnosed with blood testing — fasting glucose, hemoglobin A1c, or a glucose tolerance test. Vascular disease requires its own assessment, and the two should be pursued together rather than sequentially.
For the legs, an ankle-brachial index and arterial duplex ultrasound are the starting points, though the ABI can read falsely high in diabetes because calcified vessels resist compression, so toe pressures are often more reliable. For the neck and heart, carotid ultrasound and cardiac testing are used as clinical circumstances dictate.
What reduces the risk
Glycemic control is foundational but not sufficient on its own. Blood pressure control, cholesterol management and smoking cessation each independently reduce vascular events in people with diabetes, and the combination is what changes long-term outcomes.
Diet matters in the direction you would expect: lower in saturated fat and sodium, higher in fiber from fruit, vegetables and whole grains, with lean proteins in place of red meat. Regular physical activity improves insulin sensitivity and vascular function simultaneously.
Regular vascular screening is worth building into diabetes care rather than waiting for symptoms, especially given that neuropathy may suppress the symptoms that would otherwise prompt a visit.
The takeaway
Diabetes and vascular disease are not two separate problems that happen to co-occur. They are one process viewed from two angles, and treating them together is what protects limbs, hearts and brains. If you have diabetes and any leg symptoms — cramping when you walk, coldness, numbness, or a sore that will not heal — have your circulation evaluated rather than assuming it is neuropathy alone.