What's the difference between LDL and HDL cholesterol?

That psychedelic shot is actually a magnified image of cholesterol. See more heart pictures.
David Malin/Getty Images

We've all been told to keep our cholesterol down. High cholesterol leads to hardened arteries, coronary heart disease and even strokes. Anyone can have high cholesterol: men, women, the young, the old, the skinny and the not-so-skinny.

Cholesterol, however, gets a bad rap. Unwanted and unloved, the waxy compound earns its reputation from the company it keeps. On its own, cholesterol is quite handy around the body. It helps form cell membranes. It's crucial for growth in babies, and our bodies make most of it. So far, so good.

A cholesterol molecule is a lipid, which is a category of water-insoluble substances such as waxes, oils and fats. Because it can't dissolve in water or watery substances like blood, cholesterol can't move around in the bloodstream on its own. It has to catch a ride.

In order to travel around the body, cholesterol combines with protein, forming a lipoprotein (lipid + protein). The protein actually coats the cholesterol. However, not all lipoproteins are created equal. When the lipoprotein has more protein than cholesterol, it resembles a Ferrari, gunning through your body without stopping until the cholesterol arrives at your liver, where it's converted into bile acids. These Ferraris are high-density lipoproteins (HDLs), which most of us just call "good" cholesterol.

When the lipoprotein has more cholesterol than protein, however, this makes for a rickety ride, and that jalopy doesn't get too far. Cells have special receptors that bind tightly to these lipoproteins as they pass [source: Cohen]. This low-density lipoprotein (LDL), or "bad" cholesterol, sputters down the road, careening off the arteries, running ­into things and leaving bits all over the place. While the HDL Ferrari sees a pileup and nimbly speeds around it, the LDL jalopy crashes right into it, adding to the jumble of tangled fenders and tailpipes (or platelets and plaque).

Now the HDLs actually are kind enough to offer a lift to any stray LDLs they encounter. The problem is that our levels of HDLs and LDLs get out of whack. There are more crazy LDLs lurching around than there are responsible HDLs to pick them up. Genetics are as at fault as steak and eggs. We'll talk more about the differences between HDLs and LDLs in the next section.

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.

Testing and Reducing Cholesterol Levels

C'mon. Get your cholesterol checked. It's easy. This woman is having hers evaluated at a supermarket testing booth.
C'mon. Get your cholesterol checked. It's easy. This woman is having hers evaluated at a supermarket testing booth.
Time & Life Pictures/Getty Images

Unless your eyelids are forming yellow spots (which can happen in extreme cases), you probably won't know you have high cholesterol. You could be active, eat all the right foods, and still have high cholesterol. Genetics contribute to the condition, so blame your ancestors. In addition, your body also may have trouble properly forming or breaking down lipoproteins. Regardless, you need to get your blood cholesterol level checked, ideally at age 20, and every five years after that. Many of us probably weren't checked when we were 20 and invincible, but it's never too late to get your first cholesterol test.

When you get tested, you'll be asked not to eat or take any food , liquids or medications for 8 to 12 hours beforehand because your body still processes dietary cholesterol several hours after you've eaten a giant cheeseburger. Blood is drawn and analyzed for four different items: HDLs, LDLs, triglycerides (a type of naturally produced fat triggered by smoking, drinking, obesity or bad diet) and Lp(a), a less-understood variant of LDL. These four things will form your total cholesterol count.

For total cholesterol, we're all shooting for a level less than 200 mg/dL. People with a total cholesterol level greater than 240, which is the score for 17 percent of Americans, are twice as likely to have heart disease than people with a count of 200 [sources: AHA, CDC].

Doctors will look at the total number, as well as the individual levels of LDLs and HDLs. A high individual count of HDLs is usually a good thing; they tend to hover around 50 for men and 60 for women. People average a 3-to-1 ratio of LDLs to HDLs. Regardless of your total cholesterol number, you ideally want your LDL number to fall below 100; 130 is nudging into the danger zone. If LDLs go beyond 190, you have a cholesterol crisis on your hands [source: AHA].

But don't panic. There are things you can do to raise the good cholesterol and lower the bad cholesterol. Cutting out excess cholesterol in your diet is a good start. Dietary cholesterol is found in animal products, so limiting the meat, eggs, poultry and dairy products you consume will go a long way toward improving your numbers. In addition, you should watch your step around saturated fats and trans fats, which raise LDL levels. (You can learn more about them by reading How Fats Work.)

Smoking raises cholesterol levels, too, so that's a good reason to quit if you're looking for (another) one. Exercise also can help to increase the amount of good cholesterol. Some people may not be able to quickly lower cholesterol to a safe level solely by embracing these positive lifestyle choices, but they'll certainly have a healthier heart by doing so.

Your doctor may decide that you would benefit from medication that helps to rid your body of cholesterol. There are several different types, and generally, these medications will do one of two things. They may prevent the liver from producing too many fats or trick your body into thinking it needs to increase bile production, which requires using up cholesterol to do so. Statins (which you can learn more about by reading What are statins?) prevent the liver from producing cholesterol. Your doctor will know which medication is right for you, if one is necessary.

Now that you know more about the different types of cholesterol and how they function or malfunction in the body, you can watch what you eat, break a sweat regularly and, most important, feel more informed and confident when you call the doctor to schedule a cholesterol test.

For much more information on cholesterol and heart health, please see the next page.

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More Great Links

Sources

  • American Heart Association. "About Cholesterol." April 3, 2008. (Sept. 29, 2008) http://www.americanheart.org/presenter.jhtml?identifier=512
  • American Heart Association. "Know Your Fats." July 17, 2008. (Sept. 29, 2008) http://www.americanheart.org/presenter.jhtml?identifier=532
  • American Heart Association. "Your Heart and How it Works." (Aug. 25, 2008) http://www.americanheart.org/presenter.jhtml?identifier=1557
  • "Blood Cholesterol (HDL & LDL)." (Sept. 29, 2008) http://www.exrx.net/Testing/LDL&HDL.html
  • Centers for Disease Control and Prevention. "About High Blood Cholesterol." Nov. 8, 2007. (Sept. 29, 2008) http://www.cdc.gov/cholesterol/about.htm
  • Centers for Disease Control and Prevention. "Cholesterol: Facts and Statistics." Nov. 8, 2007. (Sept. 29, 2008) http://www.cdc.gov/cholesterol/facts.htm
  • Cohen, David E., M.D., Ph.D. "Cholesterol Metabolism and the Concept of Dual Inhibition." Lipids Online. (Oct. 2, 2008). http://www.lipidsonline.org/slides/slide01.cfm?q=ldl+receptor&dpg=1
  • Freeman, Mason W., M.D. and Junge, Christine. "The Harvard Medical School Guide to Lowering Your Cholesterol." McGraw-Hill. 2005. http://www.health.harvard.edu/newsweek/Understanding_Cholesterol.htm
  • Gordon, Jerry, Ph.D. "How Cholesterol Works." HowStuffWorks.com. April 1, 2000. (Sept. 29, 2008) https://health.howstuffworks.com/cholesterol.htm
  • Medline Plus. "Fat." May 8, 2008 (Sept. 29, 2008) http://www.nlm.nih.gov/medlineplus/ency/article/002468.htm
  • Roizen, Michael F., M.D., and Mehmet C. Oz, M.D. "YOU: The Owner's Manual." HarperCollins. 2005.
  • Schafer, Elisabeth, Ph.D., and Diane Nelson. "Cholesterol in Your Body." Iowa State University of Science and Technology. (Sept. 29, 2008) www.extension.iastate.edu/Publications/NCR332.pdf
  • WebMD. "Heart Disease Health Center." (Aug. 25, 2008) http://www.webmd.com/heart-disease/heart-disease-heart-attacks