The main difference between LDL and HDL cholesterol is that LDL is a type of harmful cholesterol whereas HDL is a type of protective cholesterol. Furthermore, LDL transports cholesterol and other fats throughout the body while HDL transports cholesterol and other fats collected from tissues to the liver.
LDL (low-density lipoprotein) and HDL (high-density lipoprotein) are two types of lipoproteins classified based on their density. Both are made up of proteins and fats. There are many other differences between LDL and HDL, but it’s important to know what cholesterol is before looking at these differences.
Key Areas Covered
1. What is Cholesterol
– Definition, Types, Control
2. What is LDL Cholesterol
– Definition, Composition, Importance
3. What is HDL Cholesterol
– Definition, Composition, Importance
4. What are the Similarities Between LDL and HDL
– Outline of Common Features
5. What is the Difference Between LDL and HDL
– Comparison of Key Differences
Key Terms
Cholesterol, Cholesterol Control, HDL, LDL, Lipoproteins
What is Cholesterol
Cholesterol is a sterol which plays a vital role in cellular metabolism as well as in producing essential substances in our body including Vitamin D, certain hormones, and bile. It is insoluble in water and transported in the blood by carriers called lipoproteins.
There are five major types of lipoproteins:
- Chylomicrons
- Very low-density lipoprotein (VLDL)
- Intermediate-density lipoprotein (IDL)
- Low density lipoprotein LDL – (bad and unhealthy cholesterol)
- High density lipoprotein (HDL) – (good and protective cholesterol)
However, too much cholesterol in the blood can increase the susceptibility to pathological conditions related to heart and blood vessels – cardiovascular diseases. Hypercholesterolemia is the medical condition which we often come across in the modern community, mainly due to inappropriate and unhealthy lifestyle practices. Every year, more than millions of people develop these abnormalities of cholesterol levels, which often go undiagnosed due to lack of attention to one’s health and wellness.
How to Control High Cholesterol Levels
High cholesterol levels in the blood can be controlled by,
- Consuming a healthy diet rich in whole grain, oatmeal, leafy vegetables, fruits.
- Cutting down excessive refined fats, modified carbohydrates, and unsaturated oils.
- Regular exercises
- Quit smoking
- Reduce consumption of alcohol
- Cholesterol-lowering drugs-Statins, according to medical advice
What is LDL Cholesterol
LDL is a type of transporter lipoprotein, which plays a central role in carrying cholesterol to places of metabolism via blood circulation. It contains high amounts of cholesterol, but lower amounts of triglycerides. Generally, LDL contains 25% protein, 46-50% cholesterol, 21-22% phospholipid, 8-10% triglycerides and cholesterol esters. Moreover, the main function of LDL is to carry fat molecules including phospholipids, cholesterol, and triglycerides throughout the body. Thus, high levels of LDL cholesterol in the blood are highly associated with a potential risk of atherosclerosis and several other cardiovascular diseases. Therefore, we call it ‘bad lipoprotein’.
Figure 1: Atherosclerosis
If we look at the pathophysiology of hypercholesterolemia associated with elevated LDL levels, there are LDL-C receptors on cell surfaces to which LDL-bound cholesterol gets attached. When these receptors are reduced due to reasons such as steatohepatitis and hypothyroidism, free LDL levels in the blood will go up, resulting in the elevation of free cholesterol in the blood. Thus, this cholesterol can get attached to blood vessel walls or lodge inside the lumen of blood vessels, creating circulation disturbances potentially resulting in atherosclerosis, thrombosis or embolism.
Here is how laboratory reports calculate the total LDL level in your blood (mg)
LDL cholesterol = [Total cholesterol] – [HDL cholesterol] – [TriGlycerides]/5
What is HDL Cholesterol
HDL is another type of transporter lipoprotein responsible for collecting fat such as phospholipids, cholesterol, and triglycerides from tissues and bringing them to the liver. Generally, it contains 33% protein, 30% cholesterol, 29% phospholipid, 4-8% triglycerides and cholesterol esters. Therefore, we call HDL ‘good’ cholesterol. Also, HDL has lots of advantages which decrease the risk of cardiovascular diseases:
- Scavenging and removing LDL-cholesterol by re-using, recycling and re-processing them with the help of the liver.
- Proper maintenance of the endothelium of blood vessels by scrubbing and cleaning cholesterol which is already attached to these walls.
A lipid profile will assess the levels of HDL-cholesterol in your blood – there should be more than 60mg/dl of HDL-cholesterol.
Figure 2: HDL
How to Achieve Healthy Levels of HDL Cholesterol
- Quitting smoking
- Reducing alcohol intake
- Consuming food rich in omega 3 fatty acids
- Cutting down unsaturated fats, modified carbohydrates, and starch
Similarities Between LDL and HDL
- LDL and HDL are two types of lipoproteins responsible for transporting hydrophobic lipids including triglycerides, phospholipids, and cholesterol through watery media including blood and extracellular fluid.
- Both contain a hydrophobic core containing cholesterol esters and triglycerides and a hydrophilic outer shell of phospholipid and cholesterol.
- Also, both play a key role in lipid metabolism.
- A lipid profile can diagnose the amount of both lipoproteins in the blood and it is possible to decide the treatments depending on the abnormalities indicated in the lipid profile.
Difference Between LDL and HDL
Definition
LDL (low-density lipoprotein) refers to a lipoprotein of blood plasma that is composed of a moderate proportion of protein with little triglyceride and a high proportion of cholesterol and associated with an increased probability of developing atherosclerosis. HDL (high-density lipoprotein) refers to a lipoprotein of blood plasma that is composed of a high proportion of protein with little triglyceride and cholesterol and is correlated with reduced risk of atherosclerosis. Thus, this is the main difference between LDL and HDL.
Good vs Bad
An important difference between LDL and HDL is that the LDL cholesterol is known to be a type of ‘bad’ cholesterol since it causes the formation of thick and hard plaques along blood vessel walls which can clog arteries, completely or partially, resulting in less flexible blood vessels. On the other hand, HDL is a type of ‘good’ cholesterol which scavenges LDL and helps to recycle them in the liver, thus reducing the level of cholesterol in the blood.
Size
The diameter of LDL is 18-25 nm while the diameter of HDL is 5-12 nm. Hence, this is also a difference between LDL and HDL.
Density
Furthermore, the density of LDL is 1.019- 1.063 g/mL while the density of HDL is 1.063- 1.210 g/mL.
Composition
LDL contains 25% protein, 46-50% cholesterol, 21-22% phospholipid, 8-10% triglycerides and cholesterol esters while HDL contains 33% protein, 30% cholesterol, 29% phospholipid, 4-8% triglycerides and cholesterol esters.
Major Lipids
The major form of lipids in LDL are cholesterols while the main form of lipids in HDL are cholesterol and triglycerides.
Type of Apoproteins
Another difference between LDL and HDL is that LDL contains Apo B-100 while HDL contains Apo A-I, Apo A-II, Apo C, and Apo E.
Function
Moreover, LDL carries lipid molecules throughout the body while HDL collects lipid molecules from tissues and brings them to the liver.
Conclusion
LDL or low-density lipoprotein is a type of lipoprotein responsible for the transport of hydrophobic lipids throughout the body. The main form of lipids transported by LDL is cholesterol. It causes the formation of thick and hard plaques along blood vessel walls, leading to atherosclerosis. Therefore, we call LDL as bad cholesterol. On the other hand, HDL or high-density lipoprotein is another type of lipoprotein responsible for collecting lipid molecules from tissues and bringing them to the liver. Therefore, it reduces the levels of cholesterol in the blood, which in turn reduces the risk of heart disease. Also, the two main forms of lipids transported by HDL are triglycerides and cholesterol. Therefore, the main difference between LDL and HDL is their composition and function.
Image Courtesy:
1. “Hdl1” By Rfch – Own work (Public Domain) via Commons Wikimedia
2. “Atherosclerosis disease progression” By Npatchett – Created by uploading user in Gimp based on a public domain image created by the US federal government (CC BY-SA 3.0) via Commons Wikimedia
