To begin with, throughout the world, cholesterol levels (measured in the blood) vary widely. Generally, people who live in countries where blood cholesterol levels are lower, such as Japan, have lower rates of heart disease.
Countries with very high cholesterol levels, such as Finland, have very high rates of coronary heart disease. However, some populations with similar total cholesterol levels have very different heart disease rates, suggesting that other factors also influence risk for coronary heart disease. High cholesterol is more common in men younger than 55 years and in women older than 55 years. The risk for high cholesterol is known to increases with age.
Cholesterol is a waxy, fat like substance that your body needs to function normally. Cholesterol is naturally present in cell walls or membranes everywhere in the body, including the brain, nerves, muscles, skin, liver, intestines, and heart.
Your body uses cholesterol to produce many hormones, vitamin D, and the bile acids that help to digest fat. It takes only a small amount of cholesterol in the blood to meet these needs. If you have too much cholesterol in your bloodstream, the excess may be deposited in arteries, including the coronary (heart) arteries, where it contributes to the narrowing and blockages that cause the signs and symptoms of heart disease.
Too many Americans have high levels of total cholesterol and LDL (the bad cholesterol). A diet high in saturated fat (a type of fat found mostly in foods that come from animals and certain oils) raises LDL levels more than anything else in your diet. You also eat cholesterol in your diet, although the effect of saturated fat in the diet is greater than the effect of dietary cholesterol.
Trans-fatty acids (seen in processed foods and many “fast foods”) can also increase LDL levels. Dietary cholesterol is found only in foods from animal products. Genetic factors combined with eating too much saturated fat and cholesterol are the main reasons for high levels of cholesterol that lead to heart attacks. Reducing the amount of saturated fat and cholesterol you eat is an important step in reducing your blood cholesterol levels.
The government has reset the standard for LDL levels so that more Americans are included in the risk group. Coronary heart disease (CHD) is caused by cholesterol and fat being deposited in the walls of the arteries that supply nutrients and oxygen to your heart. Like any muscle, the heart needs a constant supply of oxygen and nutrients, which are carried to it by the blood in the coronary arteries.
Fixed narrowing that is often calcified (hardened) usually cause angina (chest pain). Less severe narrowing may contain unstable blockages called atherosclerotic or fatty plaque. Unstable atherosclerotic plaque can rupture, resulting in clot formation, no blood flow, and a heart attack.
If enough oxygen-carrying blood is blocked from reaching your heart, you may experience a type of chest pain called angina. If the blood supply to a portion of the heart is completely cut off by total blockage of a coronary artery, the result is a heart attack. This is usually due to a sudden closure of the artery from a blood clot forming on top of unstable plaque.
A simple blood test checks for high cholesterol. Simply knowing your total cholesterol level is not enough. A complete lipid profile measures your LDL (low-density lipoprotein [the bad cholesterol]), total cholesterol, HDL (high-density lipoprotein [the good cholesterol]), and triglycerides another fatty substance in the blood. Government guidelines say healthy adults should have this analysis every 5 years.
A desirable total cholesterol level is 200 mg/dL or lower. A desirable LDL is 100 mg/dL (130-159 is borderline high; 160 is high; 190 is very high). HDL, the “good cholesterol,” should be around 40 mg/dL or greater. With HDL, the higher the number, the better, and 60 mg/dL is protective against heart disease.
Recent studies have shown that lowering cholesterol in people without heart disease greatly reduces their risk for developing heart disease in the first place. This is true for those with high cholesterol levels and for those with average cholesterol levels.
The Framingham Heart Study established that high blood cholesterol is a risk factor for coronary heart disease (CHD). Results of the Framingham study showed that the higher your cholesterol level, the greater your risk. Several studies have confirmed a direct link between high blood cholesterol and CHD. The Lipid Research Clinics-Coronary Primary Prevention Trial (LRC-CPPT) first showed that lowering total and LDL (bad) cholesterol levels significantly reduces coronary heart disease.
A series of more recent trials of cholesterol-lowering using statin drugs have conclusively demonstrated that lowering total cholesterol and LDL cholesterol reduces your chance of having a heart attack, needing bypass surgery or angioplasty, and dying of CHD-related causes.
In 1994, the Scandinavian Simvastatin Survival Study (4S) was the first study to show that people who took the cholesterol-lowering class of drugs called statins (in this case, simvastatin) reduced their risk for major CHD events (such as a heart attack) by 34%, CHD deaths by 42%, and all deaths by 30% in people with known coronary heart disease and high blood cholesterol levels, compared with people who were given a placebo (a dummy pill that looks exactly like the medication being tested).
This has been called “secondary prevention,” or prevention of a second heart attack, because the study involved people with known heart disease, many of whom had already had at least one heart attack.
The Heart Protection Study, published in 2002, examined men and women of all ages at high risk for heart disease irrespective of their cholesterol levels. Simvastatin treatment reduced CHD events by 24%. This study has caused some experts to suggest that everyone at high risk for CHD would benefit from statin therapy, regardless of their blood cholesterol levels.
Finally, The National Health and Nutrition Examination Survey III (NHANES III), carried out from 1988-1991, discovered that 26% of American adults had high blood cholesterol concentrations, and 49% had desirable values.