HDLs are involved in reverse transport; that is, they accept cholesterol from the blood and tissues and transfer it to VLDLs and LDLs for transport to the liver, where it can be degraded, disposed of, or recycled. HDLs protect the arteries from atherosclerosis by clearing cholesterol from the blood. Cardiovascular health depends greatly on low levels of total cholesterol and LDLs and a high level of HDLs. Cigarette smoking, diabetes, elevated triglyceride levels, and anabolic steroids lower HDL, whereas physical exercise, weight loss, and moderate alcohol consumption raise it.
Moderate alcohol consumption (two drinks or less per day) increases HDL cholesterol levels. An alcoholic drink is defined as a 5 ounce glass of wine, or a 12 ounce beer, or 11/2 ounces of 80 proof spirits. However, alcohol is a depressant that is responsible for nearly 50,000 traffic deaths annually and contributes to one third of all drownings and boating deaths. Alcohol impairs judgment and removes inhibitions so that people under its influence behave in ways they ordinarily would not while sober. Alcohol consumption is not an acceptable way to raise HDL cholesterol.
The higher the HDL, the greater the protection from cardiovascular disease. The average value for men is 45 mg/dl, and for women it is 55 mg/dl. This biological difference in HDL levels between genders partly explains the lower incidence of heart disease in premenopausal women as compared with men. After menopause, HDL levels in women begin to decrease, as does their protection provided by this subfraction of cholesterol. The ratio between total cholesterol (TC) and HDL (TC/HDL) should also be considered when the risk is interpreted. This ratio is determined by dividing TC by HDL. Another blood fat, the serum triglycerides, is involved in the development and progression of atherosclerosis. Average serum triglycerides, depending on age and gender, range from 50 mg/dl to 200 mg/dl.
Elevated triglycerides may not directly cause atherosclerosis, but they often accompany and add to the severity of other blood fat abnormalities. For example, high triglycerides tend to be accompanied by low HDLs, high LDLs, and high total cholesterol. This profile is predictive of the development of atherosclerosis and coronary heart disease.
A number of studies have shown that sedentary hypertriglyceridemic people can reduce serum triglycerides by as much as 45% when they participate regularly in moderately intense exercise. Physically fit people metabolize serum triglycerides more effectively than sedentary people and are able to clear them from the blood more rapidly after a high-fat meal.