Cholesterol is a waxy substance found throughout the body that helps produce healthy cell membranes, some hormones, and vitamin D. The cholesterol circulating in your blood comes from two sources: the foods you eat and your liver. However, your liver makes all of the cholesterol your body needs, so you don't need to take in more from the foods you eat. Cholesterol and other fats are transported in your bloodstream in the form of spherical particles called lipoproteins. The two most commonly known lipoproteins are low-density lipoproteins (LDL) and high-density lipoproteins (HDL). LDL is commonly called the "bad" cholesterol. It's a type of fat in the blood that contains the most cholesterol. It can contribute to the formation of plaque buildup in the arteries, known as atherosclerosis. You want your LDL to be low. To help lower it, avoid foods high in saturated fat, dietary cholesterol, and excess calories. Exercise regularly; try aerobic exercise such as brisk walking, cycling, or lap swimming. Maintain a healthy weight, and stop smoking, if you smoke. HDL is known as the "good" cholesterol. It's a type of fat in the blood that helps to remove cholesterol from the blood, preventing the fatty buildup and formation of plaque. You want your HDL to be as high as possible. Some people can raise HDL by exercising for at least 20 minutes three times a week, quitting smoking, avoiding saturated fat intake, and decreasing their body weight. For others, medicine may be needed. Because raising HDL is complicated, you should work with your doctor on a therapeutic plan. A cholesterol screening is an overall look at, or profile of, the fats in your blood. It's important to have what is called a full lipid profile to show the actual levels of each type of fat in your blood: LDL, HDL, triglycerides, and others. Talk with your doctor about how often you should be tested. Testing is important because high blood cholesterol is a significant risk factor in heart disease and stroke. Lowering blood cholesterol through increased physical activity, weight loss, smoking cessation, and proper diet decreases that risk. However, blood cholesterol is very specific to each person. For that reason, a full lipid profile is an important part of your medical history and essential information for your doctor to have. In some people who already have coronary artery disease and/or who have an increased number of risk factors for coronary heart disease, a doctor may determine that the LDL cholesterol level should be kept lower than 130. Recent studies have shown that those who are at highest risk for a heart attack should lower their LDL cholesterol level to less than 100, and that an LDL cholesterol level of 70 or less may be optimal for people at the very highest level of risk. Treatment for high cholesterol may focus on modifying your risk factors, such as lack of exercise and poor eating habits. Many people also benefit from cholesterol-lowering medications, which are used to lower lipids (fats) in the blood, particularly LDL. Statins are a group of antihyperlipidemic medications. Bile acid sequestrants and nicotinic acid are two other types of medications that may be used to reduce cholesterol levels.