Cholesterol is a type of fat manufactured by the liver. It travels in the blood attached to protein, in the form of lipoprotein. The two types of lipoprotein most often talked about in the context of cholesterol are high-density lipoprotein (HDL) and low-density lipoprotein (LDL). Blood cholesterol numbers are significant because high cholesterol increases the risk of cardiovascular diseases.
Measuring LDL and HDL Blood Cholesterol Levels
While some cholesterol is needed for healthy cell function, too much LDL cholesterol causes fatty deposits (plaques) to build up in the blood vessels. These are also referred to as atheroma, atherosclerosis or hardening of the arteries. Atheroma restricts blood flow to the heart and may lead to angina (chest pain) or blood clots, which can cause a heart attack or stroke. HDL cholesterol helps to keep the blood vessels and heart healthy.
A blood test is used to measure cholesterol levels. In the United States, blood cholesterol is measured in milligrams of cholesterol per decilitre of blood (mg/dL). In the UK, it is measured in millimoles of cholesterol per litre of blood (mmol/L). A blood cholesterol test measures total cholesterol, HDL and LDL cholesterol, all three of which are important when assessing someone's risk of coronary heart disease.
Total Blood Cholesterol Numbers
Total blood cholesterol is a number which refers to the total amount of cholesterol in the blood. A total cholesterol level of under 200 mg/dL (5 mmol/L) is ideal; this means a person has a relatively low risk of coronary heart disease.
However, total blood cholesterol numbers are not the whole story. Levels of LDL and HDL cholesterol will also need to be taken into account when assessing someone's risk of heart disease. The ratio of total cholesterol to HDL (total cholesterol divided by HDL) should ideally be 4.5 or less.
LDL Cholesterol Numbers
LDL cholesterol consists of mostly fat and a small amount of protein. Its role is to carry cholesterol from the liver to the body's cells. LDL cholesterol is referred to as "bad" cholesterol because it builds up in the blood vessels. The higher the amount of LDL cholesterol in the blood, the higher the risk of heart disease. Roughly 70% of total blood cholesterol is in the form of LDL cholesterol.
The amount of LDL cholesterol is a better indicator of the risk of heart disease than total blood cholesterol. An LDL cholesterol level of under 100 mg/dL (3 mmol/L) is desirable.
HDL Cholesterol Numbers
HDL cholesterol consists of mostly protein, and not much fat. Its role is to carry cholesterol away from the body's tissues and arteries to the liver, where it is disposed of. HDL cholesterol is referred to as "good" cholesterol because it helps to reduce blood cholesterol levels. The higher the amount of HDL cholesterol in the blood, the lower the risk of heart disease.
The amount of HDL cholesterol in the blood compared to LDL cholesterol is small. An HDL cholesterol level of 60 mg/dL (1.2 mmol/L) or higher is desirable. Due to the effects of the hormone oestrogen, women tend to have higher levels of HDL cholesterol than men.
There are other risk factors for coronary heart disease besides high cholesterol, such as smoking, obesity, blood pressure, physical activity, diabetes, age, gender, genetics and ethnicity. A person's cholesterol numbers should be viewed in the context of other risk factors he or she may have, when deciding how much blood cholesterol is healthy.
People who have high cholesterol and other risk factors for heart disease may be prescribed medications such as statins to lower blood cholesterol levels, but these drugs can have unpleasant side effects. Learn more about the side effects of statins and how simple lifestyle changes may help to lower blood cholesterol naturally.
Sources
American Heart Association. "What Your Cholesterol Levels Mean" (Accessed June 14th 2010).
Bupa. "High Cholesterol" (Accessed June 14th 2010).
MayoClinic. "Cholesterol Test Results" (Accessed June 14th 2010).
Patient UK. "Cholesterol" (Accessed June 14th 2010).
Sharon Kirby - Sharon is a freelance health writer and contributes to various print and online publications. Writing credits include Nursing Times, Good ...
