BIOLOGY Volume 2 - A Guide to General Biology - 2004

15. HEALTH AND DISEASE

15.5. Cardiovascular Diseases

15.5.2. Causes of atherosclerosis; methods for preventing cardiovascular disease

The Development of atherosclerosis is driven by A number of factors, the most critical being poor diet, Hypertension (high Blood pressure), and smoking.

DIET. Animal experiments have shown that high-fat diets promote the development of atherosclerosis. In countries like Greece and Japan, where traditional diets are relatively lean, cardiovascular diseases are less common than in Britain. Particularly dangerous are the so-called saturated Fatty acids (Section 8.7.7), which raise blood Cholesterol levels. In 1992, the Department of Health recommended that all UK residents reduce their consumption of foods rich in these acids, as well as their overall calorie intake. At the same time, It is important to remember that polyunsaturated fatty acids—abundant in vegetable oils, for example—lower blood cholesterol levels and are therefore beneficial to health.

HYPERTENSION. High blood pressure significantly increases the likelihood of cardiovascular pathology. Studies show that men under 50 with a blood pressure of 170/100 face twice the risk of dying from CORONARY Heart DISEASE compared to their peers with normal blood pressure (120/80). Hypertension has many causes: stress, obesity, smoking, alcohol abuse, and a lack of physical activity (sedentary lifestyle) sooner or later lead to a persistent rise in blood pressure. Clearly, all of these factors can be avoided through conscious lifestyle changes. Unfortunately, in some individuals, hypertension is genetically determined.

Blood pressure can be lowered using medications known as beta-blockers. Their MECHANISM OF ACTION is as follows. The hormone adrenaline exerts an excitatory effect on the body (Section 17.6.5) by binding to so-called alpha- and beta-receptors in various target Organs. Beta-blockers block beta-receptors, thereby dampening the effects of adrenaline—specifically by slowing The Heart rate and relaxing vascular smooth Muscle, which leads to a drop in blood pressure. These same drugs are helpful in treating angina pectoris because they reduce the myocardium's oxygen demand.

SMOKING. The risk of developing cardiovascular disease is substantially higher in heavy smokers. For instance, individuals under 45 who smoke more than 25 cigarettes a day are 15 times more likely to die from a heart attack than non-smokers. Smoking is linked to approximately 40% of all cases of coronary heart disease. It contributes to atherosclerosis and impairs the body's ability to break down blood clots forming around atheromas.

The effects of smoking on the body are numerous and complex.

1. Carbon Monoxide and nicotine increase the permeability of the endothelium (the inner lining of Blood Vessels) to fats and cholesterol.

2. Carbon monoxide binds tightly to Hemoglobin, reducing the oxygen-carrying capacity in smokers by roughly 15%. Oxygen deprivation in the heart muscle leads to angina pectoris and can trigger a myocardial infarction.

3. Nicotine raises blood pressure by increasing heart rate and constricting blood vessels.

4. Smokers produce higher levels of fibrinogen (a clotting protein) and exhibit lower levels of the Enzymes involved in dissolving blood clots.

5. Smoking strongly promotes platelet adhesion to the endothelium, and consequently, intravascular blood clotting.

6. Nicotine has a direct impact on elevating blood fat levels.

Smoking is the leading cause of premature death in Britain. More than a third of "excess" fatalities are due to cardiovascular diseases. The effects of smoking on the Lungs are discussed in Chapter 9.

PHYSICAL ACTIVITY. Numerous studies show that physical labor and active recreation significantly reduce the risk of cardiovascular disease. METABOLISM/18.html">The Influence of this factor on The Cardiovascular system is discussed in Section 14.7.

GENDER. Cardiovascular mortality among women is more than twice as low as among men, and these diseases typically do not develop until the onset of menopause. This is due to the detrimental effects of the male sex hormone testosterone and the protective effects of Female Sex Hormones. After menopause, blood lipid levels rise, and the prevalence of cardiovascular disease increases sharply.

Lipids are insoluble in Blood Plasma and are therefore transported in bound form. For the most part, they are packaged with Proteins to form spherical structures called Lipoproteins. These particles vary in size and density, most notably low-density lipoproteins (LDLs) and high-density lipoproteins (HDLs). HDLs contain 21% cholesterol, whereas LDLs contain 55%. Consequently, the higher the HDL and the lower the LDL levels in the blood, the better for one's health. LDLs tend to cling to arterial walls, releasing their lipids in the process and thereby contributing to The formation of atherosclerotic plaques. In men, HDL levels typically drop during Puberty, while LDL content gradually increases with age, a trend believed to be driven by testosterone. Conversely, estrogens raise HDL levels, protecting a woman's blood vessels from sclerosis from puberty until menopause. Cardiovascular diseases also occur in women, but on average about 10 years later than in men.

GENETICS. Statistical data indicate that a man's risk of heart attack is twice the average if one of his parents suffered from cardiovascular disease at a young age. If both parents had such a condition, the risk increases fivefold. Consequently, There is a hereditary predisposition to cardiovascular pathology. It is likely that the genes responsible will soon be identified, raising hopes for Methods to detect these genes in humans and thereby identify individuals at high risk.

STRESS. It is difficult to assess the severity of stress and quantify its contribution to the development of cardiovascular pathology. However, most researchers believe that psychological (emotional) stress is a major factor contributing to angina pectoris and even myocardial infarction.

AGE. Arteriosclerosis appears to be an inevitable consequence of Aging, increasing the risk of cardiovascular disease (Section 15.7).