Fat is not water soluble. Therefore, to transfer fat in blood you need a water-soluble carrier.
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What is HDL or good cholesterol?
HDL (High-density lipoprotein) cholesterol is one of the cholesterol carriers in our body. This kind of lipoproteins are commonly known as “good cholesterol” and it builds up around 20 to 30% of total blood cholesterol.
Lipoproteins are water-soluble carriers and they are protein-like particles that transfer fat-soluble fatty acids and cholesterol within the body.
HDL versus LDL cholesterol
High Density Lipoproteins (HDL) so-called “good cholesterol”: These lipoproteins contain 33% cholesterol, 2% of triglycerides, and apolipoproteins A, C, and E.
Low Density Lipoproteins (LDL) so-called “bad cholesterol”: These are the primary carriers of cholesterol and are derived from VLDL (very low density lipoprotein). These contain 42% cholesterol, 8% triglycerides, and apo-lipoprotein B100.
Very Low Density Lipoproteins (VLDL): These lipoproteins come from the liver and transfer triglycerides to different locations. This lipoprotein contains 62% triglycerides, 12% cholesterol, and apo-lipoprotein B100, E, and CII.
Chylomicrons: These contain the highest amount of triglycerides ( 90%), compared with all other lipoproteins, and carry fat from the gastrointestinal system to the muscles and fatty tissue. This lipoprotein contains also 3% cholesterol and apo-lipoprotein B, CII, and E.
The definition of low HDL cholesterol level
Adult Treatment Panel III (ATP III) recommendations have set HDL levels below 40 mg/dl as the low level; this level is the same for men and women.
According to statistics, men have lower levels of HDL than women. Based on research data, individuals with a higher HDL blood level above 50 mg/dl have a lower rate of heart disease. 
HDL and heart disease
Further studies have also confirmed that a 1% decrease in HDL cholesterol level can result in a 2% increase in heart disease rate. 
The benefits of HDL
One of the most appreciated HDL functions is its ability to extract excess cholesterol from periphery and macrophages and haul it to the liver—so-called reverse cholesterol transport. 
This lipoprotein also has an anti-oxidative activity and is able to weaken LDL cholesterol effects.
Researches suggest that HDL may have anti-inflammatory and anti-oxidative properties; they reduce the chances of blood clots and improve/maintain the vascular (endothelial) function. 
Very low HDL levels
Two genetic abnormalities could result in a low blood level of these lipoproteins.
Familial HDL Deficiency: This is an autosomal dominant disorder and it means that if you receive the gene from one of the parents then you will get the disease. Familial HDL deficiency is associated with early heart disease.
Tangier’s Disease: This is a rare disease leading to deposition of so-called foam cells (fatty deposits) in vast areas of the body; this disorder could result in early heart disease, an enlarged and fatty liver, enlarged spleen, peripheral nerve damage, and enlarged, orange-colored tonsils.
Causes of low HDL cholesterol
- Physical inactivity
- Cigarette smoking
- High carbohydrate intakes (>60 percent of total energy intake)
- Type 2 diabetes
- Medications (beta-blockers such as metoprolol, anabolic steroids, progesterone)
- Family history
- Low HDL-C often see in obese individuals
In general, in half of the population with low HDL, the cause of this abnormality is due to family history and genes and the other half due to acquired reasons as mentioned above .
Do you know your blood HDL-C level?
You should find out more and know your lipid profile as accurately as possible.
High-density lipoprotein (HDL) is a major cholesterol carrier in our bodies. These carriers transfer excess cholesterol from periphery to the liver.
Researchers confirmed that high levels of these lipoproteins could reduce the chance of heart disease; and vice versa, a low level of HDL could result in a higher risk of heart disease and stroke.