Your body needs some cholesterol. But if you have too much, it starts to build up in your arteries. (Arteries are the blood vessels that carry blood away from the heart.) This is called hardening of the arteries, or atherosclerosis. It is usually a slow process that gets worse as you get older.

the buildup of cholesterol narrows your arteries and makes it harder for blood to flow through them. It reduces the amount of blood that gets to your body tissues, including your heart. This can lead to serious problems, including heart attack and stroke.

A simple blood test tells you how much cholesterol you have. The test results are given in mg/dL of cholesterol but most people just say the numbers.

For a general idea about your total cholesterol number, compare your number to the following:

• Best is less than 200.
• Borderline-high is 200 to 239.
• High is 240 or above.

Causes high cholesterol?

• Diet. Eating too much saturated fat, trans fat, and cholesterol can raise your cholesterol. Saturated fat, trans fat, and cholesterol are in foods that come from animals (such as meats, whole milk, egg yolks, butter, and cheese), many packaged foods, and snack foods like cookies, crackers, and chips.
• Weight. Being overweight may raise triglycerides and lower “good” HDL.
• Activity level. Not exercising may raise “bad” LDL and lower HDL.
• Overall health. Diseases such as hypothyroidism can raise cholesterol. Smoking may lower HDL.
• Age. Cholesterol starts to rise after age 20. In men, it usually levels off after age 50. In women, it stays fairly low until menopause. After that, cholesterol levels rise to about the same levels as in men.
• Family. Some people inherit a rare disease called a lipid disorder. It can cause very high total cholesterol, very low HDL, and high triglycerides. If you have this problem, you will need to start treatment at a young age.

Reference Site:  health.yahoo.com