Cardiovascular Disease (CVD) and Atherosclerosis

 

The heart acts as a pump used to push newly oxygenated blood from the lungs around the body, and back again. Although several liters of blood are flowing through the heart every minute, the heart itself has its own delicate blood supply. Tiny blood vessels supply the tissues of the heart muscle itself with blood, referred to as coronary arteries. If these coronary arteries become blocked and the blood supply is cut off, then the heart muscle tissues soon begin to die and the result is a myocardial infraction, or "heart attack" – a condition that is responsible for ¼ of all deaths in Australia .

As we age, our blood vessels start to become narrower and lose their usual elasticity, a process called atherosclerosis. Eventually, this atherosclerosis leads to the development of fibrous fatty "plaques", which are responsible for the arterial hardening and narrowing. This process continues to develop, until the arteries become completely blocked, and the blood flow can no longer get through, which can result in a heart attack if it occurs in the coronary arteries, or a stroke if it occurs in the arteries of the brain (stroke is responsible for ~15%of all deaths in Astralia). You can view an excellent animation which illustrates this process by clicking here.

The most important thing to understand about the atherosclerotic process is that it is not a rapid process; it takes decades to develop, and generally begins in our early 20's. There are various things we can do which will either speed up or slow down the atherosclerotic process, so depending on our lifestyle, it could lead to heart attack or stroke by the time we are 50, 60, 70, 80, 90 or beyond. Consequently, the more we slow down the atherosclerotic process, the longer we can hold off cardiovascular disease. This may potentially mean the difference between dying in middle age, and living a long and healthy life. So, knowing this, one might reasonably want to know what things are going to increase or decrease our risk of this disease.

Non-modifiable Risk Factors

Non-modifiable risk factors are those which we have no control over. For example:

Age: The atherosclerotic process naturally increases with age, so the older we are, the greater our risk.

Sex: Men tend to be at greater risk throughout young and middle adulthood. Women's risk is not as high until after menopause.

Genetics: Cardiovascular Disease tends to run in families; consequently, having a family history will increase the risk.

Modifiable Risk Factors

Because CVD is statistically more likely to kill us than any other single cause, anything that we can do that is going to decrease our risk, is very important. Modifiable risk factors are things that we have at least some control over.

Smoking: Tobacco smoke contains chemicals which are not only carcinogenic (causes cancer) but atherogenic (speeds up the process of atherosclerosis) Smoking increases the risk of CVD perhaps more than any other modifiable risk factor.

Obesity: The risk of CVD is proportional to the degree of obesity. Even people who have no other obvious risk factors are at a very high risk of they are obese. To view an excellent animation that illustrates the effect that obesity has on health, click here.

Inactivity: Population studies have revealed that people who lead sedentary lives are at a much greater risk, even if they are not overweight. Additionally, physical activity can slow the atherosclerotic process; in fact, intervention studies have found that exercise programs significantly decrease the occurrence of subsequent heart attacks in those who have already had one.

Hypertension: High blood pressure is thought to damage the interior wall of the arteries, consequently speeding the rate of atherosclerosis. Hypertension is a factor in approx 75%of all strokes and heart attacks. Most disturbingly, mild to moderate hypertension may have no noticeable symptoms, and it is thought that approximately 30% of all cases go undiagnosed. Taking your blood pressure is very quick and simple, and, just is the case with regular cancer screening, regular checkups may potentially lead to early intervention. If hypertension is diagnosed, it is important to get it under control and keep it under control using medication, dietary interventions, and healthy weight management.

Abnormal Biomarkers: There are certain biomarkers that can be used to assess the risk of CVD; these are things that can be measured with a blood test. When levels of these biomarkers become abnormal, the risk of CVD increases. Such biomarkers include:

Cholesterol: Cholesterol plays an important role in our body, and is required for various functions, however can become problematic when our blood levels rise too high. Most of our cholesterol is synthesized in the liver, and carried throughout the blood stream to various organs in our body in particles called Low Density Lipoproteins (LDL). If our LDL-Cholesterol levels become too high, they start to get lodged in our arteries where they become oxidized and contribute to the formation of "foam cells" which are part of the atherosclerotic process. If some of this cholesterol gets taken away from our arteries and back to the liver, it travels in High Density Lipoproteins (HDL). Because HDL takes cholesterol away from the arteries, higher levels are thought to be protective, and are sometimes referred to as "good cholesterol" Because LDL carried cholesterol to the arteries where they contribute to the "clogging” effect, LDL-Cholesterol is referred to as "bad" cholesterol. Because the LDL-C levels is usually higher than the HDL-C levels, the Total Cholesterol (TC) levels can be used as an indication of CVD risk, however the ratio of LDL:HDL is a far more accurate measure.

Triglycerides: The other type of lipid (fat) which, when elevated, significantly increases the risk of CVD are triglycerides. Most standard fasting blood tests will measure both LDL:HDL cholesterol levels as well as triglyceride levels.

Homocysteine: Homocysteine is an amino acid which is converted from methionine. When homocysteine levels become elevated, the risk of CVD increases. This problem can be controlled by prescribing therapeutic doses of folic acid, vitamin B6 and Vitamin B12.

C-Reactive Protein (CRP): CRP is marker indicative of the type of inflammation that occurs in CVD. As with cholesterol, triglyceride and homocysteine concentrations, elevated levels increase the risk of CVD and needs to be controlled.

Diet: The other major modifiable risk factor is diet; this includes both avoiding that "bad" (foods and dietary habits that increase the risk) and ensuring the "good" (foods and dietary habits that decrease the risk; thus having a protective effect. Foods and other substances that decrease the risk of CVD are called "cardio-protective". Cardio-protective foods include:

Fruits and Vegetables: Diets rich in fruits and vegetables significantly decrease the risk of CVD. It is recommended that adults consume at least 2 servings of fruit and 5 servings of vegetables daily. Because it is not known precisely which fruits and vegetables offer the best protection, it is important to ensure a wide variety. Garlic is perhaps the only vegetable known to have significantly measurable cardio-protective effects in clinical trials, as it is known to protect against LDL oxidation and have favorable effects on blood pressure.

Wholegrain foods: Population studies have found that wholegrain foods also have a significantly protective effect on the risk of CVD. Wholegrain foods (such as whole meal bread and pasta, oats etc) possess many cardio-protective substances, help lower blood cholesterol and blood glucose (have a low GI) and help protect against Diabetes.

Fish: Population studies have found that regular (2 to 4 serves weekly) consumption of fish (specially fatty fish such as salmon)decreases the risk of heart disease and stroke. Clinical trials have also found that fish and fish oil supplementation significantly lowers blood triglyceride levels and decreases the incidence of heart attacks in intervention studies. It is thought that the Omega 3 fatty acids DHA and EPA in fish are responsible for its cardio-protective effect, however fish is also a rich source of protein, vitamin D and various trace minerals such as selenium, which are not present in fish oil supplements.

Red wine: Population studies have also found that moderate wine intake also decreases the risk of CVD. This was first identified among the French population; a phenomenon referred to as the "French paradox" because of their low rate of heart disease despite a diet high in animal fats. It is thought that moderate alcohol consumption (1 standard drink per day) may help protect against heart disease, however consumption of other alcoholic beverages also increases the risk of other diseases such as cancer. Red wine contains not only alcohol, but other phytochemicals which are thought to contribute to its cardio-protective effect.

Nuts: Population studies have demonstrated a lower risk of CVD among people who consume moderate quantities of nuts (approx 1 serve per day). Clinical trials have found that various nuts (especially walnuts and almonds) can lower LDL-Cholesterol levels.

Olive Oil: Despite consuming as much fat as Americans, the Mediterranean people have a lower incidence of heart disease; a phenomenon thought to be at least in part due to their olive oil consumption. Olive oil, particularly extra-virgin olive oil, possesses several cardio-protective properties, and is considered a "good" fat.

Soy and legumes: Legumes are not only rich sources of many nutrients, they posses a significantly low GI and a lot of soluble fibre which helps not only lower blood sugar but lowers cholesterol levels as well. Foods made from soy beans have been shown to exert a particularly cardio-protective action, by improving the LDL:HDL ratio, protecting against LDL oxidation and lowering triglyceride levels.

Others: There are other specific foods and beverages which are thought to decrease the risk of CVD by improving serum cholesterol levels. These foods include green tea, plant-sterol fortified margarines, psyllium husk and oat bran. The lactobacillus bacteria in yoghurt and probiotic supplements have also been shown to lower cholesterol levels as well as exert a protective effect on blood pressure. Recent studies have also found that cocoa and dark chocolate can improve serum cholesterol levels, inhibit LDL oxidation, lower blood pressure and improve insulin function.