I run health and fitness seminars for corporate groups, and I mention in these talks that exercise aids in reducing “bad” cholesterol. The other day, I had someone ask me how this happens. I didn’t know the answer, and I can’t find anything in any of my text books that actually explains how exercise aids in the process. Can you help me out?
Cholesterol is an essential nutrient necessary for many functions in the body including repairing cell membranes, manufacturing Vitamin D and production of hormones. Regardless of these benefits, when cholesterol levels rise in the blood, they can have dangerous consequences, depending on the type of cholesterol.
Low Density Lipoproteins (LDL) - The "Bad Cholesterol"
The primary villain in the cholesterol story is low density lipoprotein (LDL). In a major study, the lowest incidence in heart disease was found among people with lowest LDL levels. Low density lipoprotein (LDL) transports about 75 percent of the blood's cholesterol to the body's cells. It is normally harmless. However, if it is exposed to a process called oxidation, it can penetrate and interact dangerously with the walls of the artery, producing a harmful inflammatory response. Lowering LDL is the primary goal of cholesterol drug therapy.
High Density Lipoproteins (HDL) - The "Good Cholesterol”
HDL appears to benefit the body in two ways. First, it removes cholesterol from the walls of the arteries and returns it to the liver. Second, it helps prevent oxidation of LDL. HDL then helps keep arteries open and reduces the risk for heart attack. High levels of high density lipoprotein (HDL), above 60 mg/dl, may be as important for the heart as low levels of LDL. HDL levels below 40 mg/dl are considered to be harmful. In one study, for each 4 mg/dL decline in HDL levels, there was a 10 percent increase in coronary artery disease.
Effects of Exercise on Cholesterol Levels
The majority of studies comparing endurance athletes to sedentary controls or the general population reported that athletes have lower LDL levels, with leaner athletes frequently having the lowest values. Although it appears that endurance training may decrease LDL, there is little information about the biochemical mechanism producing this change.
Endurance-trained athletes have much higher HDL values compared to sedentary populations. The primary reason for the elevation in HDL is an increase in lipoprotein lipase activity in response to exercise. Lipoprotein lipase accelerates the breakdown of triglycerides, resulting in a transfer of cholesterol and other substances to the HDL. Burning at least 250 calories a day (the equivalent of about 45 minutes of brisk walking or 25 minutes of jogging) seems to confer the greatest protection against coronary artery disease, most likely because it raises HDL levels. It is interesting to note that healthy patients whose physical activity was restricted to bed rest for three to six weeks because of some type of traumatic fracture showed a significant decrease in HDL levels.
In addition to aerobic training, there are a few studies suggesting that resistance training may also improve lipid and lipoprotein profiles. Decreases in total cholesterol and LDL have been reported for both men and women. However, the alteration of personal lifestyle habits in conjunction with a decrease in body fat and increase in fat free mass may contribute to these favourable changes.