Cholesterol is not soluble in the blood and has to be transported within the body by carriers known as lipoproteins. HDL, or high-density lipoprotein, carries cholesterol from the arteries to the liver and thus lowers the amount of free cholesterol in the blood and reduces your risk of coronary artery disease.
Regulation of HDL
The amount and quality of HDL is regulated mainly by the amount of triglycerides in your body. The level of triglycerides increases as fat deposits in your abdomen increase. These increased triglycerides are incorporated into VLDL particles that activate the CETP, or cholesterol ester transfer protein. CETP acts as a lipid shuttle that exchanges the cholesterol esters present in HDL with triglycerides. The resultant triglyceride-rich HDL particle is dysfunctional and less effective in cholesterol transport from the peripheral arteries to the liver, resulting in more LDL or bad cholesterol, and progressive atherosclerosis.
Metabolism of HDL
The metabolism of HDL is a complex process. It occurs by a process called reverse cholesterol transport. The cholesterol esters present in LDL cholesterol in the peripheral cells are oxidized and then taken up by scavenger cells in your body known as macrophages. From the macrophages, where the cholesterol esters are converted into free cholesterol, a transport protein known as ABC-1 or ATP Binding Cassette Protein -- 1 transfers the free cholesterol to nascent HDL particles in the intestine. These nascent particles are then converted into mature HDL particles that are then taken up by the liver, where the free cholesterol is liberated and excreted into the bile.
Abnormalities of HDL Metabolism
HDL levels below 40 mg/dL. increase the risk for atherosclerosis, reports the American Heart Association. You may have low levels of HDL if you suffer from diabetes, smoke are overweight or don't engage in physical activity. Certain medications, such as anabolic steroids and progestin, may also decrease your HDL levels. Many people are genetically predisposed to have low HDL levels.
How to Increase HDL levels
HDL levels can be raised by a regular exercise programme that includes 30 minutes of aerobic exercise at least five times a week, as recommended by researchers at The Johns Hopkins University. A reduction in smoking and mild-to-moderate alcohol consumption also raises the HDL cholesterol levels. Nicotinic acid, or vitamin B 3, is prescribed by doctors to increase HDL levels. Dietary control, with an increase in consumption of monounsaturated fatty acids, is also recommended.
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