What is LDL cholesterol?
LDL (low-density lipoproteins) attach cholesterol molecules and carry them around in the body where cholesterol is needed.
The reason LDL is required for cholesterol movement is that cholesterol is a fat molecule.
Fats are insoluble in water and cannot move in the bloodstream and hence lipoproteins such as LDL are required for this job (1)
Where LDL-Cholesterol is produced?
LDL is produced in the liver as very-low-density lipoprotein (VLDL) which is processed further by enzymes to eventually make LDL (2).
Cholesterol is also produced in the liver (endogenous) but it is also obtained from external sources such as animal-based fat (exogenous).
In both cases, the majority of cholesterol is transported via the blood by LDL to peripheral cells.
HDL High-density lipoproteins (HDL) move cholesterol in the opposite direction. HDL transports excess cholesterol from the body back to the liver and other tissues such as gonads and adrenals.
Thus HDL removes cholesterol from the bloodstream which minimizes the potential to form plaques (3).
For this reason, HDL is often referred to as Good Cholesterol.
What are the functions of Cholesterol?
Cholesterol gets a bad name due to its association with the different disease conditions but cholesterol itself is NOT bad.
In fact, it is an essential molecule in our bodies and has several important functions. The most important function is to maintain the outer covering of the cells called the cell membrane (4).
It is also required for the production of
- Steroid hormones (e.g. cortisol, aldosterone, adrenal androgens, testosterone, estrogens, and progesterone)
- Bile acids (required for the absorption of vitamins A, D, E, and K)
- Synthesis of Vitamin D
Why is LDL bad Cholesterol?
If it is such an essential molecule in the body, Why is LDL bad Cholesterol?
LDL is called “bad cholesterol” because it is the lipoprotein that carries most of the cholesterol in the bloodstream.
It is easily oxidized and binds to arteries where it can cause the buildup of atherosclerotic plaques (5).
Excess of everything is bad. Our bodies do not require cholesterol in high quantities to function properly (6).
High levels of LDL-Cholesterol, described as Hypercholesterolemia are associated with atherosclerotic plaque formation (7).
Atherosclerosis is a condition in which the blood flow in the arteries is severely hindered by a build-up of atherosclerotic plaques which are composed of oxidized LDL, macrophages and other cells.
The plaque formation may lead to severe health conditions such as stroke and heart attack (8).
Although, plenty of published research has shown LDL role in cardiovascular diseases (9).
Recently published studies have argued against this long-held position (10).
It is posited that at least dietary cholesterol (exogenous) increases do not lead to total cholesterol increase due to a decrease in cholesterol production in the body (endogenous) (11).
The role of HDL is important in this regard. In fact, the low level of HDL-cholesterol has shown to increase the risk of heart disease (12).
What LDL level is good?
The guidelines by Adult Treatment Panel III (ATP III) has defined the following levels of LDL (13).
|Optimal||100 mg/ dL|
|Near-optimal (upper and lower limit)||100 to 129 mg/dL|
|Borderline high||130 to 159 mg/dL|
|High||160 to 189 mg/dL|
|Very High||More than 190 mg/dL|
Thus, the optimal levels of LDL-cholesterol are lower than 100mg/dL.
This should not be confused with total cholesterol levels for which less than 200 mg/dL is considered a good level (14).
The LDL level alone should not be the only parameter to look at when considering the risk of disease.
The relative serum concentration of HDL-LDL is considered a better risk indicator compared to individual parameters for cardiovascular disease (15).
It is posited that individuals with LDL above 190 mg/dL and HDL below 40 mg/dL have a high risk of forming arterial plaques whereas LDL below 100 mg/dL and HDL above 50 mg/dL is associated with no risk (16).
|High risk||No risk|
|LDL more than 190mg/dL HDL less than 40mg/dL||LDL less than 100mg/dL HDL more than 50mg/dL|
Why is the LDL-Cholesterol level high?
There are 3 major causes of LDL-Cholesterol to increase.
Genetics is an important consideration when looking for reasons for elevated levels of LDL. The most important one is familial hypercholesterolemia, which results in a defect in LDL receptor genes.
- Secondary causes
The secondary causes are the ones that are not directly related to LDL genes.
These include hypothyroidism, nephrotic syndromes, cholestasis, pregnancy, and certain drugs like cyclosporine, thiazide, and diuretics (17).
A diet high in fats tends to increase the level of LDL and total cholesterol in the body (18).
How to lower the LDL-Cholesterol?
Based on research a number of strategies have been suggested.
These include diet, lifestyle changes, and medication.
- Better Diet
Taking a healthy diet is crucial to keep the LDL-Cholesterol at low levels (19).
- Vegetables and fruits
- Whole grain
- Food high in fiber
- Fish (omega-3)
Eliminate or reduce the consumption of foods that have
- Saturated fats
- Trans fats
Diets such as the Mediterranean diet that constitute fibrous foods and low quantities of saturated fats can be helpful.
- Lifestyle changes
Making changes to basic habits can improve the levels of LDL.
- Not smoking,
- Exercising regularly
- Losing weight
Medications are normally used to lower LDL levels. The most popular and effective class of medicines called Statins are often recommended by physicians to patients with high LDL levels (20).
LDL is considered bad cholesterol because the increased levels of LDL are correlated with a high risk of diseases related to the vascular system.
LDL levels below 100mg/dL are considered optimal whereas LDL levels above 190mg/dL are considered high. LDL levels are affected by genes, secondary causes, and diet.
By making changes in diet, lifestyle and medication one can mitigate the increased levels of LDL.