There are two main theories as to the cause of atherosclerosis:

• Unhealthy levels of cholesterol in the blood damage the walls of the arteries. The cholesterol causes an inflammatory reaction that allows fatty materials to accumulate.
  
  
• Repeated injury to the walls of the artery from the immune system or direct toxicity.

In both of these theories, there is a change in the arteries that leads to the development of fatty materials, known as atheromas. It is believed that these theories are not completely separate and are most likely related to each other in the cause of the disease.

Atherosclerosis is also thought to involve inflammation as certain white blood cells are present during the development of the disease. These cells move out of the bloodstream into the artery walls, where they are transformed into foam cells. These foam cells collect cholesterol and other fatty materials which in turn form atheromas. The atheromas cause a hardening and thickening of the artery wall.

Hardening of the arteries occurs over time, which means the older a person is the greater the risk for developing the disease. Most cases of atherosclerosis are found in middle–age and older adults. Men and individuals with a family history of premature cardiovascular diseases have an increased risk of atherosclerosis.

There are several additional conditions that increase the risk of developing atherosclerosis. Some of the risk factors can be controlled, such as diet, but others cannot be controlled, such as family history.

Diabetes is one such disease that increases the risk of atherosclerosis. Researchers believe that higher glucose levels damage blood vessels, creating a greater likelihood of developing cardiovascular problems. Characteristics for diabetes and atherosclerosis include:

• People with type 1 diabetes may be more likely to develop arteriosclerosis in the small arteries, such as those in the eyes and the kidneys, and sometimes in the large arteries.
  
  
• People with type 2 diabetes are more likely to develop atherosclerosis in the large arteries, such as in the heart.

People with diabetes tend to develop atherosclerosis at an earlier age and more extensively than nondiabetics. The risk of developing atherosclerosis is 2 to 6 times higher for people with diabetes.

Additionally, individuals with diabetes may have a number of related factors that increase the risk for atherosclerosis. These risk factors include:

• High blood pressure. This condition has long been recognized as a major risk factor for atherosclerosis and cardiovascular disease. When a person has high blood pressure and diabetes, a common combination, the risk for cardiovascular disease doubles.

• Dyslipidemia. High levels of LDL "bad" cholesterol and triglycerides and low levels of HDL "good" cholesterol contribute to the development of atherosclerosis. Dyslipidemia is frequently present in diabetes patients.
  
  
• Obesity. Being significantly overweight greatly increases the risk of cardiovascular disease. Abdominal obesity is closely associated with type 2 diabetes as well as high blood pressure and high cholesterol, leading to atherosclerosis.
  
  
• Smoking. Research has documented that tobacco smoking contributes to cardiovascular disease. Smoking has been shown to:
  
• • Decrease HDL cholesterol
    
  • Increase LDL cholesterol
    
  • Damage artery walls with increased carbon monoxide in the blood
    
  • Constrict arteries, further limiting the blood flow
    
  • Increase the blood's tendency to clot by making platelets stickier
    
    
• Physical inactivity. Inactivity appears to increase the risk of cardiovascular disease, whereas regular exercise appears to reduce the risk. In addition, a sedentary lifestyle is often associated with diabetes and high blood pressure.
  
  

Other risk factors for atherosclerosis include age, family history, stress, sleep apnea, alcohol abuse and possibly elevated bloodstream levels of homocysteine, an amino acid.

Many of the risk factors for atherosclerosis are related. An increase in weight can cause an increase in cholesterol and blood pressure. In addition, many of the associated risk factors are commonly found in people with diabetes. With each of these factors, a diabetic person has a greater chance of developing atherosclerosis and cardiovascular complications.