Cholesterol is one of two fats in the bloodstream called lipids. Your liver makes almost all the cholesterol in your blood. Eating high cholesterol low saturated fat foods (such as eggs and shellfish) does not increase your blood cholesterol. The other fat is triglyceride. Almost all triglyceride comes from what we eat or is made in the liver from foods that have a lot of sugar or starchy carbohydrates. Fat does not dissolve in the blood, so these fats are carried in tiny droplets within a protein shell. These proteins are called lipoproteins. Any of these lipoproteins can be elevated without the others, so although many people may say, ”I have high cholesterol,” it is important to know what kind of ”high cholesterol” they have. In this post I will talk about the different kinds of hyperlipidemia (the medical term for high cholesterol), what kind of damage they can do, and how they can be treated both with medicines and diet.
Types of lipoproteins
There are four major classes of lipoproteins: chylomicrons, very low density lipoproteins (VLDL), low density lipoproteins (LDL) and high density lipoproteins (HDL).
Chylomicrons
Chylomicrons are the largest particles. They carry fat that you eat from the intestine to be used as fuel for the body or stored in fat cells. They are made mostly of triglycerides (90%), which is in the center of the particle with several different kinds of lipoproteins on the outside.
VLDL (very low density lipoproteins)
This is the next smallest class of particles. They contain about 50% triglycerides, 25% cholesterol and the rest a type of fat called phospholipids. They are made in the liver and carry triglycerides and cholesterol to the cells.
LDL (low density lipoproteins)
LDL particles carry more cholesterol than the others. They also deliver cholesterol to the cells. High levels of LDL particles are associated with an increased risk of heart disease. More about this later.
HDL (high density lipoproteins)
HDL particles have the most protein and the least amount of fat contained within them. That makes them more dense, hence the name, high density lipoproteins. The function of HDL particles is to carry cholesterol and triglycerides back from the cells to the liver. This decreases LDL in the cell walls of the arteries and helps prevent heart disease. Low levels of HDL are associated with increased risk of heart disease and high levels with decreased risk of heart disease. Paradoxically, very high levels of HDL actually increase the risk of heart disease.
Cholesterol
Cholesterol is essential to your body. Cell walls are made up of mostly cholesterol. Cholesterol is used to make many essential hormones in the body including estrogen, progesterone, androgen, cortisol and many others. Cholesterol moves in and out of cells to do it’s job. If LDL (and therefore cholesterol) is too high, it can accumulate in the walls of arteries at spots where there is inflammation. More about inflammation later. The immune system sends special cells called macrophages to ”eat” the offending LDL particles, but that causes more inflammation and more accumulation of cholesterol. This cholesterol buildup is called a ”plaque” and these can cause narrowing of the artery and can also cause blood clots to form which can completely block the artery. The result is a heart attack or stroke.
Triglycerides
Triglyceride levels are affected by what we eat. We absorb triglycerides directly from eating saturated fats but the liver also converts any unneeded calories to triglycerides that are then stored in fat cells. Very high triglyceride levels can cause pancreatitis (inflammation of the pancreas). It is likely that high triglycerides also increase the risk of heart disease and stroke, possibly by being deposited in the arterial walls like cholesterol. We are not sure at this point the exact mechanism that connects high triglyceride with cardiovascular disease
Inflammation
Inflammation in the artery walls starts the whole process of cholesterol buildup and plaque formation. In fact, one of the main reasons that statin drugs like atorvastatin (Lipitor) work is that they reduce inflammation in the walls of the arteries as well as lowering LDL (and thus cholesterol). It may well be that inflammation of the artery walls can cause plaque formation to begin even in people with normal LDL levels. We can get some idea how much chronic inflammation is going on in our bodies by having a blood test called high sensitivity C-reactive protein (CRP).
So what causes inflammation of the artery walls and is there anything we can do about it?
Inflammation is increased by our old friends: highly processed foods, sugar, high fructose corn syrup and a diet high in starchy carbohydrates. There is pretty good evidence to suggest that eating large amounts of saturated fats (essentially animal fats) also produces inflammation. Increased belly fat secretes a substance that causes chronic inflammation (See my previous post Why is the United States so fat and what to do about it for instructions about how to measure your belly fat). Finally, inflammation of the gums from plaque on your teeth leads to inflammation in arteries. Of course smoking cigarettes also increases inflammation in your arteries.
You can reduce inflammation in your arteries by stopping smoking if you are a smoker, eating unprocessed foods, especially fresh vegetables, fruits and berries, nuts and fatty fish. Taking good care of your teeth also helps. That means flossing daily and seeing the dentist for cleaning once every 6 months. Regular exercise such as walking at least five times a week also reduces inflammation. If your abdominal circumference is above normal, then losing weight will reduce inflammation. All of these things also tend to reduce LDL and triglycerides too, so you get double duty from these life style behaviors.
When you need to take medicine for hyperlipidemia
A significant portion of high LDL and/or triglycerides is genetic. You can make all the lifestyle changes I talk about above and still have high lipids. If that is the case, then you need to talk to your doctor about starting cholesterol medicine. That will likely be one of the class of drugs called statins. There are quite a few of these and they vary in potency, side effects and drug interactions. Almost everyone will be able to tolerate one of the statins without any significant side effects. There are a few people that have adverse reactions to all of the statins. There are some new non-statin medicines that look promising for decreasing LDL in those few patients who can’t tolerate statins. Your doctor will help you find the right medicine for you to help lower your LDL and/or triglycerides.
Bottom Line
All fats in the blood are carried by special proteins called lipoproteins. Cholesterol is carried mainly by LDL. In the presence of inflammation in the arteries, high levels of LDL lead to plaque formation in the arteries that can eventually lead to heart attack or stroke. High levels of triglycerides also increase the risk of heart disease. Lifestyle changes can reduce both inflammation and number of LDL particles and triglycerides, thus reducing population risk of cardiovascular disease. Sometimes lifestyle changes are not enough and cholesterol lowering medicines are needed.