Final answer:
The largest risk factor for the expansion of an AAA is atherosclerosis, often associated with advancing age, along with hypertension, diabetes, and lifestyle factors such as obesity and smoking.
Step-by-step explanation:
The largest risk factor for expansion of an abdominal aortic aneurysm (AAA) is atherosclerosis. Atherosclerosis, which is often associated with advanced age, leads to a progressive narrowing and hardening of the arteries, promoting the formation and expansion of aneurysms. Factors like hypertension, diabetes, obesity, poor nutrition, lack of physical activity, and tobacco use significantly exacerbate arteriosclerosis and atherosclerosis, increasing the risk of aneurysm expansion or rupture. It's crucial to manage these risk factors to prevent the progression of AAA, and in some cases, surgical intervention may be recommended to address blockages or weakened vessels.