This is by far the most common and most important abnormal condition found in the human body. The basic process consists of deposits of fatty materials which are readily visible as yellow streaks and mounds in the inner lining of the arteries. The deposits tend to be irregular in extent and location; they can be present to an excessive degree in one location, as for example, in the coronary arteries of the heart, with only slightto-moderate involvement elsewhere.
When it is widespread and advanced. the condition is sometimes spoken of as “generalized arteriosclerosis;” disorders produced by this condition are traceable to impairment of the circulation. Decreased circulation results from the fatty deposits, which encroach on the caliber of the blood vessel. In addition, there is a local slowing of the bloodstream, which can result in the formation of thromboses or clots, When this occurs in an artery of the heart, a coronary thrombosis (heart attack) is the result: if the vessel involved happens to be one in the brain. a stroke (with paralysis) may result. If the clot is in an important vessel going to the lower extremities, death (gangrene) of the tissue there will follow.
It was formerly thought that atherosclerosis was a normal aging phenomenon in arteries. It is now regarded as a disease process which tends to increase with aging but which is variable and partially, if not largely, preventable. Many factors can contribute to the degree of atherosclerosis, although there is uncertainty about their relative importance. Some of these are:
1. The level of such blood fats as the neutral fats called triglycerides and the wax-like fat called cholesterol; when these are elevated, the degree of atherosclerosis is increased.
2. High blood pressure, which tends to increase atherosclerosis,
3. Sex hormones. All else being equal, female sex hormone protects against, and male sex hormone tends to favor, atherosclerosis. Hence, till the menopause, the female has a distinct advantage over the male in this respect.
4. High saturated-fat diets. It appears that diets in which the saturated fats are reduced and the polyunsaturated fats increased may favorably affect atherosclerosis.
5. Cigarette smoking. This appears to increase the likelihood of coronary thrombosis-presumably by some effect on atherosclerosis there.
6. Metabolic disorders such as diabetes and hypothyroidism. These significantly increase the rate of atherosclerosis.
The possibility that atherosclerosis may be controllable by diet has excited widespread attention and has resulted in a changing pattern in the fat consumption of Americans. Probably overweight also tends to increase atherosclerosis.