The thoracic aorta is the biggest artery of the body. It lives within the chest doing its job of delivering blood flow from the heart to all the other arteries of the body. The aorta is located just under the sternum, initially above the heart as it aims headward, then turning left and downward towards the abdomen, pelvis, and legs.

Forces within the body can work to weaken the aorta. When the aorta is weakened, it enlarges. Enlarged aortas also tend to grow atherosclerotic plaque. Plaque in the aorta poses risk for stroke and mini-strokes ("transient ischemic attacks," or TIAs), since plaque is prone to fragmentation that releases little bits of debris that usually flow up into the arteries of the brain.

Enlarged aortas are fairly common, particularly in people with high blood pressure and cholesterol abnormalities, as well as those who are overweight or smoke. The simplest method to be screened for an enlarged aorta is with ultrasound of the heart, an echocardiogram. The first inch of two of the aorta is readily seen and can be measured.   

Conventional thinking is that, once an aorta enlarges (3.7 cm or greater is the cutoff), it will inevitably continue to enlarge at the average rate of 2.0 mm per year (adding up to 1.0 cm enlargement over 5 years). Once the aorta reaches 4.5 cm in diameter, it is classified as an aneurysm. For this reason, conventional discussions on the topic of thoracic aortic aneurysms all say something like "Enlarged aortas should be monitored yearly. Surgical replacement should proceed when the aorta reaches a diameter of 5.5 cm."

This is because an aortic diameter of 5.5 cm is associated with much greater likelihood of rupture. Ruptured aortic aneurysms are fatal within just a few minutes. Alternatively, the internal lining of the enlarged, weakened aorta can tear, a "dissection," in which the tissue-thin lining of the diseased aorta tears away, allowing blood to get beneath it and "dissect" along the length of the aorta. This is excruciating and can be life-threatening if not remedied immediately. Surgery for both aortic aneurysms and dissections involves opening the chest and usually replacing the aortic valve and inserting a synthetic aorta. The procedure is high-risk, especially if any branch arteries of the aorta are involved.

So putting a stop to any further aortic enlargement is a worthwhile goal. Conventional thought is that there is nothing you can do to stop the inevitable growth of the thoracic aorta.
Nonsense. There are a number of efforts you can make to halt further increase in aortic diameter and minimize, if not eliminate, the risk for developing an aneurysm or dissection of the aorta.

There are two categories of factors that cause the aorta to become weakened and increase in diameter:

1) Internal pressure--Think of blood pressure (BP) as the internal inflating pressure on this aortic "balloon." Keeping the "inflating pressure," i.e., blood pressure, low exerts substantial effect on slowing growth of aortic diameter. I aim to keep BP low (less than 130/80, preferably 100/70). (While this may seem extreme by modern day standards, humans living a natural hunter-gatherer lifestyle have BPs typically 90-110 systolic, 60-75 diastolic.)