What is cholesterol and triglyceride? How are they transported in the blood?
Lipids are waxy, fat like substances in the blood. The two important fats (lipids) in the blood are cholesterol and triglycerides. Just like a droplet of oil floating in water, lipids do not dissolve in blood. Hence, they are packaged with special proteins called Apolipoproteins. This complex of protein and lipid is called a lipoprotein.
Each lipoprotein molecule has varying quantities of cholesterol and triglycerides.
What are the different types of lipoproteins?
The protein component decides the density of the lipoprotein particles. Low density lipoprotein (LDL) has lower protein while High density lipoprotein (HDL) has higher protein.
There are 5 types of Lipoproteins:
- Chylomicrons - It transports dietary fats as triglycerides in the blood circulation to muscles, fat cells or liver.
- Very Low Density Lipoproteins (VLDL) - It transports triglycerides from liver to muscles and fat cells.
- Intermediate Density Lipoproteins (IDL) - VLDL converts to IDL and then to LDL. It transports both cholesterol and triglycerides.
- Low Density Lipoproteins (LDL) - It transports most of the cholesterol, deposits in the lining of blood vessels and plays an important role in atherosclerosis.
- High Density Lipoproteins (HDL) - It removes excess cholesterol from the tissues and takes it to the liver for further breakdown.
The cholesterol mass carried by LDL and HDL is referred to LDL cholesterol ( LDLc ) and HDL cholesterol ( HDLc ) respectively. The cholesterol carried by LDL, VLDL, IDL and Lipoprotein (a) is associated with damage to the lining of the blood vessels and plaque formation. This is a reflection of the atherogenic cholesterol mass carried in the blood. The cholesterol carried by HDL does not cause damage to the lining of the blood vessels and hence is non atherogenic.
What is Non HDL cholesterol ( Non HDL-c)?
Non HDLc is the measure of all the atherogenic cholesterol mass carried by LDL, VLDL, IDL and lipoprotein (a). It is calculated by subtracting the HDL cholesterol from Total cholesterol.
What are Apolipoproteins?
Apolipoproteins (often abbreviated as Apo) are proteins that bind to lipids (fats) to form lipoproteins in the bloodstream.There are several different types of apolipoproteins, each with specific functions in lipid transport and metabolism.
Some of the key apolipoproteins include: Apolipoprotein A (ApoA): ApoA is a major component of high-density lipoproteins (HDL). It plays a central role in the reverse cholesterol transport process, which involves removing excess cholesterol from peripheral tissues and transporting it back to the liver for excretion.
Apolipoprotein B (ApoB): It is significant because it is a key protein found in LDL ( Apo B 100) and VLDL ( Apo B 48) particles, which transport cholesterol and triglycerides in the blood. Each lipoprotein particle carries one ApoB and hence it is a measure of the particle numbers. Elevated ApoB levels are associated with a higher risk of cardiovascular diseases, making it a crucial marker for assessing and managing heart disease risk.
What is Lipoprotein (a)?
It is often abbreviated as Lp(a) and is a type of lipoprotein in the blood that consists of a cholesterol-rich LDL particle attached to a unique protein called apolipoprotein(a). Elevated levels of Lp(a) are a risk factor for cardiovascular diseases, as it can promote atherosclerosis and increase the risk of heart attacks and strokes. It is genetically determined and commonly found amongst those belonging to asian ethnicity especially Indians.
What is GOOD cholesterol AND BAD cholesterol?
While the amount of cholesterol in your LDL and HDL type particles may vary, the cholesterol they represent is the same and, hence, terminology like “bad” cholesterol and “good” cholesterol are actually incorrect. Instead, it is the number of the particles that can cause plaque formation and damage the lining of the blood vessels.
What is the source of cholesterol and Triglycerides in the circulation?
Most of the cholesterol that our body needs is produced by the liver and food contributes very minimally to the amount of cholesterol in our blood.
The kind of diet that we have determines the amount of triglycerides in our blood. Excess sugar, high carbohydrate diets, excess alcohol consumption, uncontrolled diabetes, obesity are some of the common reasons for rise in Triglcerides.
How do carbohydrates impact our health?
There is compelling evidence to suggest that excess carbohydrate intake is associated with worsening of metabolic health. It's not just the quantity of carbohydrates that we consume, it's the quality. These 'bad carbs' such as refined cereals, white bread, sugar-sweetened drinks or fruit juices, etc. should be restricted and consumed only in moderation, if at all. These can be replaced by the 'good carbs' such as whole grains, legumes, vegetables, whole fruits, nuts and seeds. This is a paradigm shift in food consumption and needs to be encouraged in the interests of avoiding the vagaries of metabolic diseases.
Nearly 80-90% of cholesterol is synthesised by the liver. Lifestyle does not have a significant impact on LDL cholesterol (the bad cholesterol). The levels of triglycerides are decided by external factors like diet, exercise, weight, alcohol, diabetes, thyroid issues, etc. Excessive carbohydrate intake in our diet (more than 60%), leads to an increase in triglyceride production by the liver which contributes to excess VLDL in the circulation.