Lipids are insoluble, which means that they cannot dissolve in water and thus travel through your body in solid form. LDL and HDL are two types of lipids that contribute to the total amount of cholesterol in your blood. Although LDL and HDL both represent cholesterol, they have very different structures and roles in your body.
Lipoproteins
Because lipids are insoluble, they need to be packaged in protein carries called lipoproteins to travel throughout the blood. Lipoproteins are capsule-shaped carriers that contain an outer and inner shell. The outer shell is high in protein and phospholipids, while the inner shell carries insoluble fat and cholesterol. Lipoproteins are categorized based on how much protein and cholesterol they contain, which is referred to as their density.
LDL
LDL, or low-density lipoprotein, contains a high amount of cholesterol and only a small amount of protein. This particular cholesterol-to-protein ratio allows LDL to deliver the cholesterol to your cells, but it is also the reason that LDL deposits excess cholesterol into your bloodstream, which accumulates on your artery walls. This accumulation of cholesterol leads to a condition called atherosclerosis, which increases your risk of heart disease. Because LDL increases your heart disease risk, doctors often refer to it as "bad cholesterol."
HDL
HDL, or high-density lipoprotein, contains a high level of protein and only a small amount of cholesterol. The protein shell of HDL is responsible for picking up excess cholesterol in your bloodstream and carrying it back to your liver so that your body can remove it. Because HDL removes excess cholesterol, doctors often refer to it as "good cholesterol."
LDL Goals
Since LDL cholesterol contributes to the accumulation of plaque on your arteries, the goal is to get your LDL numbers as low possible. The American Heart Association recommends that most healthy adults aim for an LDL level of less than 100mg/dL. If you have heart disease or risk factors for heart disease, such as high blood pressure, you should aim for an LDL level of less than 70mg/dL.
HDL Goals
Because HDL removes excess cholesterol from your arteries, you should try to get your HDL values as high as possible. The American Heart Association defines an HDL level of 60mg/dL or higher as protective against heart disease. If you are a woman and your HDL falls below 50mg/dL or a man whose HDL is below 40 mg/dL, your risk of heart disease increases.
References
- American Heart Association; Good vs. Bad Cholesterol; July 21, 2010
- "Nutrition and You"; Joan Salge Blake; 2008
- American Academy of Family Physicians; Cholesterol: What Your Level Means; November 2010
