People with untreated or poorly treated diabetes have too much sugar (glucose) in their blood. High blood sugar levels can damage the lining of arteries and speed the buildup of fat and calcium in blood vessel walls (hardening of the arteries or atherosclerosis).

When hardening of the arteries occurs in the heart's blood vessels (coronary arteries), the heart muscle receives less blood flow and oxygen. Atherosclerosis occurs more often and at a younger age in people who have diabetes than in people who do not have diabetes.

Strict control of blood sugar levels and other factors, such as blood pressure, cholesterol, and eliminating smoking, in people with diabetes may prevent or delay the start of heart disease.