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5.1.1: What Are LDL and HDL

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What is LDL?
LDL is a type of cholesterol that stands for low density lipoprotein. It is usually considered the "bad cholesterol." It is considered bad because of its increased risk of creating plaque buildup. LDL is used in measuring the risk of heart disease. It consists of an outer ring of lipoprotein surrounding a cholesterol center.
What is HDL?
HDL is a type of cholesterol that stands for high density lipoprotein. This cholesterol is usually considered the "good cholesterol." It is considered good because it takes cholesterol to the liver to be disposed of since cholesterol can't be dissolved in blood. HDL along with LDL are used to measure the risk of heart disease.
LDL Structure
LDL structure is composed of around 50% cholesterol and 25% protein. LDL molecules are much smaller and denser than HDL molecules. Since they are smaller and less dense, they are more likely to go through oxidation and accumulate on on arterial walls as plaque. LDL proteins contain "B-100" proteins.
HDL Structure
HDL structure is around 20% cholesterol and 50% is protein. HDL molecules are larger and more buoyant than LDL molecules. They are less likely to cause plaque buildup because of their structure. These molecules contain mainly A-1 and A-II proteins.
LDL Function
The main function of LDL is to carry cholesterol to different parts of the body. Since it takes cholesterol to different parts of the body, it is more likely to build up on arterial walls. This leads to an increased risk of heart disease. That is why LDL is usually called the "bad cholesterol."
HDL Function
HDL's main function is to take cholesterol from your heart and other organs to the liver to be disposed of. This is why it is considered to be the "healthy cholesterol." Some cholesterol is good so only the excess is carried away and disposed of.
Why do doctors monitor the concentrations of LDL and HDL in patient's blood?
During a blood test, LDL and HDL are both monitored along with other things because they are used to help evaluate the patient's risk of heart disease. Whether more cholesterol is being taken to or from cells can be determined during a blood test. HDL levels should be at least 40mg/dL or closer to 60mg/dL. LDL should be lower than 129mg/dL or even lower for people that are at higher risks for heart disease.
How are concentrations of LDL and HDL associated with the risk for heart disease?
An excess of LDL can result in plaque buildup on arterial walls which can ultimately result in atheroscerlosis. That is the hardening of the arteries and can lead to heart diseases like a heart attack or stroke. Unlike LDL, higher HDL levels can actually lower the risk of heart disease.
What can patients do to change the levels of LDL and HDL in their blood?
Several things can be done to change the levels of both LDL and HDL in your blood. A healthy diet with reduced fat and cholesterol will increase HDL levels and decrease LDL levels. Saturated fat intake should be limited 7% or less of total calories, cholesterol should be 200mg per day or less, and Omega 3 fatty acids will increase HDL levels. It has been found that physical activity can raise HDL levels 5%. The activity needs to be consistent with at least 30 minutes a day for 5 days a week. An estimated every six pounds that are lost can increase HDL by one and lower LDL by one. Medication can also be used with the other things above.
Other molecules monitored in patient's blood
- triglycerides
- blood sugar level
- total cholesterol