percentage of men having high HDL-cholesterol (see graph below). The proportion of men with this protective level increased significantly for each 10 mile increment in weekly mileage up to 49 miles per week. The National Cholesterol Education Program has identified HDL-cholesterol of 35 mg/dL or less as a risk factor for heart attacks. The percentage of men with clinically-defined low HDL-cholesterol was six-fold greater in the lowest mileage group as compared to the highest mileage group (graph on top right). Fat in the blood is carried principally in the form of triglycerides. Higher plasma triglyceride levels are associated with increased heart disease risk. The figure below shows that running more miles was associated with significantly lower triglyceride levels.