Recent studies on cholesterol and heart disease suggest that for each 4 mg/dl increase in the HDL level is associated with a 10 % reduction in risk of adverse coronary events.
HDL is called "good" cholesterol because this form cholesterol goes from the arteries to the liver to get removed from the body. LDL on the other hand is the ("bad") cholesterol; it combines with other substances that can form plaques on the walls of arteries. Theses plaques stack up over time cause occlusion (narrowing down) and hardening of the arteries. Also, the rough surface of plaque is a suitable environment for blood to clot to form and sit, sometimes leading to complete blockage of the affected artery.
The new guidelines from the National Cholesterol Education Program say that HDL levels below 40 mg/dl are classified as low and are associated with a higher risk of coronary heart disease, while HDL levels of 60 mg/dl or above are classified as high and considered protective against heart disease.
HDL and LDL levels are determined by a number of factors, including heredity, diet, weight, exercise, age, gender, alcohol consumption, and stress. A high HDL level is a safeguard against coronary artery disease, so do not worry.