High-density lipoprotein (HDL) cholesterol is known as the "good" cholesterol because it helps remove other forms of cholesterol from your bloodstream. Higher levels of HDL cholesterol are associated with a lower risk of heart disease.

Cholesterol is a waxy substance that's found in all of your cells and has several useful functions, including helping to build your body's cells. It's carried through your bloodstream attached to proteins. These proteins are called lipoproteins.

• Low-density lipoprotein cholesterol. High levels of low-density lipoprotein (LDL) can eventually build up within the walls of your blood vessels and narrow the passageways. Sometimes a clot can form and get stuck in the narrowed space, causing a heart attack or stroke. This is why LDL cholesterol is often referred to as "bad" cholesterol.
• High-density lipoprotein cholesterol. HDL cholesterol is often referred to as "good" cholesterol. HDL picks up excess cholesterol in your blood and takes it back to your liver where it's broken down and removed from your body.

If you have high LDL and low HDL cholesterol levels, your doctor will probably focus on lowering your LDL cholesterol first. Medications known as statins — such as atorvastatin (Lipitor) and simvastatin (Zocor) — are the most common treatment for high LDL cholesterol.

Cholesterol levels are measured in milligrams (mg) of cholesterol per deciliter (dL) of blood or millimoles (mmol) per liter (L). When it comes to HDL cholesterol, higher numbers are better.

To some extent, people who have naturally higher levels of HDL cholesterol are at lower risk of heart attack and stroke. It's less clear whether that same benefit holds true for people who increase their HDL levels with medications.

Lifestyle changes known to increase HDL, such as moving more, quitting smoking or improving your diet, have been shown to lower the risk of heart attacks, However, medications that specifically increase HDL levels have failed to reduce the rate of heart attacks.

Oddly enough, people who naturally have extremely high HDL levels — above 100 mg/dL (2.5mmol/L) — appear to be at higher risk of heart disease. This may be caused by genetic factors.

HDL levels are typically lower in people who have metabolic syndrome — a cluster of conditions that include obesity, increased blood pressure and high blood sugar levels.

Besides helping you lose weight, increased physical activity can lower your triglycerides, the most common type of fat in your body, while increasing your HDL levels. Benefits can be seen with as little as 60 minutes of moderate intensity aerobic exercise a week.

In terms of diet, try to avoid trans fats, as they can increase LDL cholesterol and lower HDL cholesterol levels. Foods prepared with shortening, such as cakes and cookies, often contain trans fats, as do most fried foods and some margarines. Limit saturated fat, found in meats and full-fat dairy products, as well.

If you smoke, find a way to quit. Smoking lowers HDL levels, especially in women, and increases LDL levels and triglycerides.

Moderate use of alcohol has been linked with higher levels of HDL cholesterol. For healthy adults, that means up to one drink a day for women of all ages and men older than age 65, and up to two drinks a day for men age 65 and younger.

However, if you don't drink, don't start drinking to raise your HDL cholesterol levels. Too much alcohol can cause weight gain, and might increase your blood pressure and triglyceride levels.

HDL levels are sometimes improved by drugs used to lower LDL and triglyceride levels — such as prescription niacin; fibrates such as gemfibrozil (Lopid); and certain statins, particularly simvastatin (Zocor) and rosuvastatin (Crestor).

But clinical trials for several drugs specifically designed to increase HDL levels were halted early because they didn't reduce the risk of heart attacks.

Drugs containing testosterone and other anabolic steroids can lower your HDL cholesterol levels. Avoiding these drugs may help increase your HDL numbers.