Biochemistry

Definition of Good and Bad Cholesterol

You may know someone who is concerned because a blood test has revealed higher-than-normal cholesterol levels. To understand the problem, you need to know a bit more about this molecule.

Cholesterol is not water-soluble, so it travels in the bloodstream encased in proteins. The resulting packets of cholesterol and protein are called lipoproteins, and they occur in low- and high-density varieties.

Low-density lipoprotein (LDL) particles carry cholesterol to the arteries. Excess LDL cholesterol that does not enter cells may accumulate inside blood vessels, blocking blood flow to the heart. Less blood flow means low oxygen delivery, which can damage the heart’s muscle. Too much LDL cholesterol (commonly called “bad cholesterol”) therefore increases the risk of heart attack.

In contrast, high-density lipoproteins (HDL) carry cholesterol away from the heart and to the liver, which removes it from the bloodstream. High levels of HDL cholesterol (“good cholesterol”) promote heart health. Fortunately, it is possible to raise your HDL level. Exercising, losing weight, avoiding trans fats, and replacing meat and dairy with unsaturated dietary fats are among the most effective strategies.

Cholesterol-lowering statin drugs like Lipitor can reduce the risk of heart attack by lowering LDL levels, although they typically have little effect on HDL. These drugs block a liver enzyme that normally helps produce cholesterol; they also boost the liver’s ability to get rid of LDL.

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