LDL cholesterol definition and meaning
Low-density lipoprotein (LDL) labeled as the “bad cholesterol”, is a combination of a moderate portion of proteins, a little of triglycerides, and a major proportion (about 50%) of cholesterol.
You find cholesterol mainly in the blood and the tissue cells, and about 80% of it is produced in the liver. The body makes the rest of the 20% from the foods that we eat.
LDL is a type of cholesterol, which again is a type of lipid (fat). Cholesterol can be defined as the most common type of steroid compound in the body.
It is a soft and waxy substance in nature and does not dissolve in blood. It, therefore, needs a vehicle or a carrier to transport itself through the blood.
The soluble proteins in the blood do the job and help the cholesterol to reach the cells in the various parts of the body and carry out its functions, which are absolutely essential to us.
Cholesterol piggy rides on the protein to facilitate its transport through the blood and this combination is called Lipoprotein (lipo meaning fat).
Types of Lipoproteins
There are three major types of lipoproteins moving in the bloodstream.
- LDL – Low-Density Lipoproteins, the bad cholesterol
- HDL – High-Density Lipoproteins, the good cholesterol
- VLDL –Very Low-Density Lipoproteins, again the bad cholesterol
All these types of lipoproteins don’t just carry cholesterol, they also taxi triglycerides, phospholipids, fat-soluble vitamins, antioxidants, and of course proteins.
Low-density lipoproteins contain B-100 proteins, while HDL particles contain mostly A-I and A-II proteins. The type of protein determines the function of the lipoprotein particle and is, therefore, significant.
Why the name “LDL”?
Low-density lipoprotein or LDL is so called because it has a low density of or low amount of proteins and is mostly fat.
It is called bad cholesterol because higher than normal LDL levels can give rise to serious health complications, which besides others include heart attack, stroke, and peripheral vascular disease.
Low-density lipoproteins transport the cholesterol from the liver through the blood for uptake by the body cells of various tissues. This helps in the formation of the cell wall and also keeps up the cell nutrition.
Structure and composition of LDL
LDL comprises 10% triglycerides, 45% cholesterol, 22% phospholipid, and 25% protein. As you can see, cholesterol makes up the bulk of LDL.
LDL particles average 22 nm in diameter with about 3000 lipid molecules in total, and they contain approximately 170 triacylglycerols (a systematic chemical name for triglyceride), 1600 cholesterol esters, and 200 unesterified cholesterol molecules.
Esters are nothing but organic compounds in which the hydrogen of the acid is replaced by an alkyl or another organic group.
LDL cholesterol is converted into cholesteryl esters to more efficiently transport both the dietary and synthesized cholesterol through the bloodstream.
Free cholesterol that is present in the lipoproteins is confined only to the outer surface of the lipoprotein particle. When it is converted into cholesteryl esters, more of it is packed into the interior of the lipoprotein particle. This vastly increases the capacity of lipoproteins to transport cholesterol through the blood.
LDL blood levels reference range
As per the Adult Treatment Panel III (ATP III) guidelines, cholesterol levels after 9 to 12 hours of fasting are as follows:
- < 100 mg/ dL – Optimal
- 100-129 mg/dL – Near optimal
- 130-159 mg/dL – Borderline high
- 160-189 mg/dL – High
- >190 mg/dL – Very high
In 2004, a panel of physicians lowered the “safe” level of LDL cholesterol from 130 to 100 mg/dL and further recommended that people who are at high risk of developing cardiovascular disease should aim to lower their LDL levels to 70 mg/dL.
Is LDL good or bad?
It is as the universal saying goes: “Everything within limits is good; it’s when you cross the limits that things begin to go bad”.
It could not be more true with LDL. Within limits, LDL serves its important functions at the cellular level to build the cellular wall, feeding and protecting the cells, helping in the absorption of fat-soluble vitamins A, D, E, and K and more.
When it crosses its normal blood levels and rises above 100 mg/dL, it starts showing its dangers or rather its badness. However, note that the parameters of the cholesterol values vary slightly by age. Even children with a family history are known to have elevated levels.
With high levels, the excess LDL invades the endothelium layer of the arterial walls and gets oxidized. This attracts the macrophages (WBCs), which envelope the LDL particles and get deposited on the inner walls of the arteries forming plaques. This is called atherosclerosis.
These plaques narrow the arterial lumen over time and reduce blood flow. This can happen in the arteries of the heart and/or the brain and can subsequently lead to a heart attack or a stroke.
These plaques narrow the arterial lumen over time and reduce blood flow. They can rupture and form clots within the arteries. This can happen in the arteries of the heart and/or the brain and can subsequently lead to a heart attack or a stroke.
Functions of LDL cholesterol. Why do you still need LDL?
That our body requires LDL is a fact because of its benefits that can be termed only as “essential”. Do read its benefits before you label LDL as a nuisance to your body. Both HDL and LDL have their functions to perform. They deliver cholesterol to different parts of the body and that is where their essential functions differ.
Low-density lipoproteins primarily transport cholesterol through the bloodstream to feed the countless cells in the various tissues of the body.
Functions of LDL in brief:
- LDL Cholesterol helps to synthesize vitamin D in the skin from sunlight exposure.
- The precursor to the production of the steroid hormone pregnenolone.
- It plays a vital role in cognitive function.
- LDL helps in the formation of the cell wall.
- It helps in the absorption of fat-soluble vitamins A, D, E, and K. Without LDL cholesterol, you could be deprived of these essential vitamins.
- LDL plays a vital role in nerve cells (neurons) communicating with each other and exchanging electrical signals.
However, letting your LDL blood levels rise is definitely something you do not want, Just keep those levels within healthy limits and let the LDL do its job.
Causes of high LDL cholesterol levels
There is an in-depth post on factors that cause high cholesterol.levels in the body. Here, I will state those in brief.
Causes that increase your LDL cholesterol blood levels:
- Hereditary cause
- Regularly eating a diet rich in saturated fats and trans fats
- Obesity causes your cholesterol levels to rise
- Diabetes type 2
- Alcoholism
- Sedentary lifestyle
- Chronic smoking
- Continuous stress
- Older age
- Large waist circumference
- Hypothyroidism
- Long-term use of certain medicines
How do you reduce LDL cholesterol and keep it within normal limits?
Due to its “badness”, high levels of LDL need to be lowered and brought down within normal blood levels.
There are medical ways to do it with drugs and there are non-medical or natural ways to do it.
Firstly, preference is given to the non-medical way because cholesterol medication (statins) once started can become a lifelong commitment and secondly, they have their side effects such as liver and muscle damage plus neurological problems.
But, as explained above, very high LDL levels may require being treated with medication without delay. The American Heart Association describes the parameters of LDL levels and the risk factors in patients who should be started with statins immediately.
The non-medical or natural ways to lower LDL cholesterol levels include:
- Avoid high saturated fat foods
- Follow the low-cholesterol diet
- Do aerobic exercises daily
- Have a healthy lifestyle
- Eat natural foods that have cholesterol-lowering properties.
All these will help you to stay off the cholesterol drugs that once started, can be a lifelong commitment. Secondly, they have their side effects, which include liver and muscle damage and neurological problems. Following the above five posts will not only keep your lipid profile healthy but also keep you overall healthy.
Secondly, test your blood regularly, especially if you have a family history and after the age of 35 years. Understand your LDL, HDL, and triglyceride numbers and the cholesterol ratios that tell your doctor about the quantum of your risk of heart disease. Know when and how often to test for cholesterol. The link on their numbers above will tell you just that.