Blood levels of LDL cholesterol (LDL-C) are often assessed when evaluating the risk of future heart disease.
Cholesterol is a fat substance. Fats are insoluble in water and can therefore not be transported in blood on its own.
The body’s solution to this problem is to bind cholesterol to certain proteins that function as transport vehicles carrying different types of fats such as cholesterol, triglycerides (TG) and phospholipids. These combinations of fats and protein are termed lipoproteins.
The amount of cholesterol carried in different lipoproteins can provide important information about the risk of developing cardiovascular disease (CVD).
LDL-C is an important marker for the risk of developing heart disease.
Available evidence suggests that lowering blood levels of LDL-C reduces the risk of CVD.
According to the European Society of Cardiology, the results of epidemiological and clinical trials confirm that the reduction of LDL-C must be of prime concern in the prevention of CVD.
Cholesterol is an organic molecule included in the sterol family.
Sterols are chemical substances, classified as lipids or fats, although they are chemically different from other types of dietary fat, such as triglycerides and phospholipids. Unlike triglycerides, sterols contain no fatty acids. Cholesterol is the best-known sterol, mainly because of its proposed role in atherosclerosis and cardiovascular disease.
Cholesterol is a major structural component of cell membranes and is especially abundant in nerve and brain tissue. It is also a precursor molecule. For example, vitamin D is synthesized from cholesterol.
Cholesterol is also a precursor of important hormones such as progesterones, glucocorticoids (cortisol), mineralocorticoids (aldosterone), androgens (testosterone) and estrogens.
Cholesterol occurs only in foods of animal origin.
Because the body can synthesize cholesterol, it is not needed in the diet.
Most of our cholesterol is synthesized by the liver. Studies have shown that increasing dietary cholesterol may reduce synthesis, although probably not by an equivalent amount.
A standard lipid panel provides information about the amount of cholesterol carried by different lipoproteins.
There are five major types of lipoproteins; chylomicrons, very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), low-density lipoprotein (LDL) and high-density lipoprotein (HDL).
LDL is called low-density lipoprotein because LDL particles tend to be less dense than other kinds of cholesterol particles.
HDL cholesterol (HDL-C) is often termed the “good” cholesterol while LDL-C is usually termed the “bad” cholesterol.
LDL Cholesterol (The Bad Cholesterol)
Elevated levels of LDL-C in the blood are associated with increased risk of atherosclerosis and heart disease.
There are special receptors on cell surfaces that bind LDL-C, these are called LDL-receptors. A lack of LDL-receptors may reduce the uptake of cholesterol by the cells, forcing it to remain in the circulation thereby raising blood levels.
In familial hypercholesterolemia, which is a genetic disorder, the body is unable to remove LDL from the blood. This leads to high levels of LDL-C in the blood, which may severely increase the risk of cardiovascular disease, even at a young age.
Blood tests typically report LDL-C. These numbers are usually based on calculation, using the Friedewald formula that includes total cholesterol, HDL-C, and triglycerides. This formula relies on the assumption that the ratio of triglyceride to cholesterol is constant, which is not always the case.
Here is how LDL Cholesterol is calculated:
If mg/dl is your unit, like in the United States the formula looks like this:
LDL colesterol = [Total cholesterol] – [HDL cholesterol] – [TG]/5
If mmol/l is your unit like in Australia, Canada, and Europe the formula looks like this:
LDL cholesterol = [Total cholesterol] – [HDL cholesterol] – [TG]/2.2
Thus, LDL-C calculations may have limitations when blood triglyceride levels are either high or low. Direct LDL -C measurements are also available, but are less often done due to higher costs.
Cholesterol levels are measured in milligrams (mg) of cholesterol per deciliter (dL) of blood in the US and some other countries. Canada and most European countries measure cholesterol in millimoles (mmol) per liter (L) of blood.
Some studies show that the number of LDL particles (LDL-P) may be a better predictor of risk than LDL-C. LDL particle size may also be important when assessing risk.
How Is LDL Cholesterol Interpreted?
It is considered important to keep cholesterol levels, especially LDL-C within certain limits. If you have other risk factors for heart disease, such as high blood pressure, diabetes, or if you smoke, keeping LDL-C low becomes even more important.
Here you can see how LDL-C levels are looked at in terms of risk:
- above 190 mg/dL (4.9 mmol/L) is considered very high
- 160 – 189 mg/dL (4.1 – 4.9 mmol/L) is considered high
- 130 – 159 mg/dL (3.4 – 4.1 mmol/L) is considered borderline high
- 100 – 129 mg/dL (2.6 – 3.3 mmol/L) is considered near ideal
- below 100 mg/dL (below 2.6 mmol/L) is considered ideal for people at risk of heart disease
- below 70 mg/dL (below 1.8 mmol/L) is considered ideal for people at very high risk of heart disease
How Can You Influence Your LDL Cholesterol?
If your LDL-C is high, your doctor will probably suggest lifestyle changes. Quitting smoking will be helpful and so may eating whole grain, oatmeal, olive oil, beans, fruit, and vegetables. Most doctors will recommend eating less fat from meat and dairy products.
Regular exercise is desirable. Losing weight may be helpful.
Some studies show that low-carbohydrate diets may positively affect LDL particle size and number.
If lifestyle changes don’t help, your doctor may suggest medications that lower cholesterol. So-called statins are the most commonly used drugs for lowering cholesterol.
Studies have shown that statins improve prognosis among patients with coronary artery disease. Their role for treatment of raised LDL-C in healthy people (primary prevention) is less clear. The decision to give statins in primary prevention is usually based on other risk factors as well as the LDL-C value itself.