What's the difference between LDL and HDL cholesterol?

My Body Makes Cholesterol?!

Your body doesn't need these eggs for their cholesterol. It already has its own internal supply.
Your body doesn't need these eggs for their cholesterol. It already has its own internal supply.
© iStockphoto.com/Dominik Kraner

You can stop eating cholesterol for the rest of your life and still have high levels. How can this be? For starters, all of your cells can create cholesterol. This is good because every cell in your body needs it to form protective membranes. Your body actually monitors your cells, and if it senses that a cell doesn't have enough cholesterol, it will produce more. Cholesterol also is an essential building block for naturally produced vitamin D and other good stuff, like estrogen and testosterone. But even though every cell can make its own cholesterol, some cells need extra help with their supply. This is where your liver comes in.

Your body, mainly your liver, produces 75 percent of your cholesterol; your small intestine also aids in both the creation and absorption of cholesterol [source: AHA]. The average diet adds another 300 to 500 mg of cholesterol [source: Schafer]. This external cholesterol comes from animal and dairy products. But even if you eat foods without cholesterol, the carbs, fats and proteins all break down eventually and release carbon, which your liver turns into cholesterol.

If your liver thinks the ovaries need more cholesterol to produce estrogen, the organ produces new cholesterol, bundles it with a protein in the form of an LDL and sends it into the bloodstream. When that LDL leaves your liver, any cell that needs it can claim it. Your liver can produce about 1,000 mg of cholesterol a day, so this stuff is always present [source: Gordon]. To reclaim unused LDLs, your liver bundles cholesterol into HDLs, which pass through your body and collect stray LDLs. When these lipoproteins return to the liver, it recycles them or uses them to build bile acids, which the intestine absorbs for use in digestion.

It's a pretty amazing system, but it's imperfect. Genetics plays a part in controlling cholesterol levels, but some people are better at self-regulating than others. If they consume too much dietary cholesterol, their bodies accordingly slow down the natural production of this waxy substance. Other people, though, can take in too much cholesterol and their bodies don't limit production.

As you age, plaque tends to build up in the lining of your arteries. Some of those fatty deposits may be made of excess LDLs. This plaque buildup can result in the arteries hardening and narrowing at the site of the blockages, a condition called atherosclerosis.

The problem is that LDLs are like low-quality spackle. Eventually some of that spackle might break loose, and when that happens, your body is going to try to heal the nick that has developed in the plaque itself. This clotting can totally block your arteries, resulting in heart attack or stroke. The HDLs can prevent this from happening since they remove wayward LDLs from these trouble areas and back to the liver. This is why HDLs are "good" -- they lower the risk of heart attack by trying to rid your blood vessels of excess LDLs.

Now that we know more about good and bad cholesterol, we'll talk about how you can make sure you have the right amount of each.