According to the National Heart, Lung and Blood Institute, heart disease is the leading cause of death in the United States. A million Americans suffer from heart attacks each year, and half a million die from heart disease. One of the major causes of heart disease is an increase of lipids such as cholesterol in the blood. Controlling cholesterol through exercise and other methods is important: A 1 percent reduction in serum cholesterol levels can result in a 2 to 3 percent reduction in the risk of coronary heart disease.
Definition
Cholesterol is a waxy lipid used to synthesize hormone molecules, form bile secretions that aid in digestion, and serve as a structural component in cell membranes to make them fluid and permeable. Cholesterol travels through the body in the circulatory system. However, fat can't mix with water, the main ingredient of blood, so before entering the blood stream, various fats such as cholesterol are coated with a protein. This package is referred to as a lipoprotein.
Types
There are generally two main types of lipoproteins in the blood. The most abundant form is known as low-density lipoproteins, or LDL. If LDL levels get too high, then it can contribute to the cellular alterations of the inner arterial wall in the blood and lead to the development of plaque. The second type is called high-density lipoprotein, or HDL. It transports cholesterol from the tissues and blood to the liver for excretion from the body or synthesis into bile acids. It also prevents the uptake of LDL at receptor sites in the body. Therefore, the presence of HDL in the blood is considered a good thing. HDL contains more high-density proteins than lipids in its structure.
LDL
LDL is sometimes called the "bad cholesterol" due to the fact that it can sometimes promote an unhealthy lipid state in the blood. MayoClinic.com reports that an LDL count below 130 mg/dL---milligrams per deciliter, the main method of measurement in the blood---is considered optimal. A count below 100 mg/dL must be achieved for people at risk of heart disease. LDL should represent between two-thirds and three-quarters of the lipoproteins in your blood.
Significance
Len Kravitz, Ph.D. and Vivian Heyward, Ph.D. of the University of New Mexico report that people with high aerobic fitness do tend to experience lower LDL levels over time, but studies that have investigated the change in blood cholesterol after exercise have shown variable results. A biochemical mechanism that allows exercise to lower cholesterol has not yet been established.
Considerations
There are a few explanations for the studies. Exercise could correlate with, and not necessarily cause, low blood cholesterol, or the relationship could be too complex for a post-workout blood test to completely elucidate. Nevertheless, exercise is just one aspect of maintaining a healthy lifestyle. A healthy diet, abstinence from smoking, medication and body fat also matter. These factors help control the synthesis of cholesterol in the body. In that sense, exercise is useful in another way: If it helps you lose weight, then the state of your blood lipid levels should greatly improve.
