"Cholesterol" is a household word, but still an elusive concept for many people. And no wonder. Biochemistry is hardly simple, even for biochemists. Here are a few cholesterol review notes.
Cholesterol is a fat-like substance found in all animal cells, human and otherwise. It is essential to life. The human body manufactures all the cholesterol it needs—thus we can live without eating any cholesterol. Cholesterol is attached to protein packages called lipoproteins, which are assembled in the liver and circulate in our bloodstream. Two of the better known types of lipoproteins are HDL (high-density lipoprotein), the "good" type that carries cholesterol out of the system; and LDL (low-density lipoprotein), the "bad" type that deposits cholesterol in arterial walls, where it can build up and narrow the arteries. High LDL cholesterol is a known risk factor for heart attack.
The chart below will refresh your memory on guidelines for total cholesterol and HDL cholesterol. In the U.S., cholesterol is measured in milligrams per deciliter (mg/dL) of blood. In Canada and many other countries, it's measured in millimoles per liter (mmol/L). The latter is known as the International System. (To convert to millimoles, divide the milligrams by 38.67. To convert from millimoles to milligrams, multiply by 38.67.)
Optimal: Less than 100 mg/dL (2.58 mmol/L)
Desirable:100-129 mg/dL (2.58 -3.34 mmol/L)
Borderline-high: 130-159 mg/dL (3.37 -4.11 mmol/L)
High: 160 mg/dL or more (4.14 mmol/L or more)
Desirable: Less than 200 mg/dL (5.2 mmol/L)
Borderline-high: 200-239 mg/dL (5.2 -6.19 mmol/L)
High: 240 mg/dL or more (6.2 mmol/L or more)
Low: Less than 40 mg/dL (1.03 mmol/L)
Optimal: Less than 100 mg/dL (1.13 mmol/L)
Desirable: Less than 150 mg/dL (1.69 mmol/L)
Borderline-high: 150-199 mg/dL (1.69-2.25 mmol/L)
High: 200-499 mg/dL (2.26-5.63 mmol/L)
Very high: 500 mg/dL (5.74 mmol/L)
How often should I have my blood cholesterol measured?
Adults should be screened at least once every five years, but more frequently if their total cholesterol is elevated or close to being elevated, if HDL is low and/or they have other cardiac risk factors.
My total cholesterol is below 200, but my HDL is only 30. Is this a problem? I'm a 45-year-old man.
An HDL below 40 mg/dL is a risk factor for heart attack, even if total cholesterol is in the desirable range. One study showed that the risk of dying from heart disease was 38 percent higher in men with HDL under 35, even if their total cholesterol was below 200. Stroke risk in such men was higher, too. If your total and LDL cholesterol are elevated, a high HDL can help protect you somewhat. The higher your HDL, the better.
I'm a woman of 55, and my HDL has markedly declined during the last five years. Why?
At menopause, estrogen production declines, and so does HDL. Female sex hormones tend to raise HDL.
How can I raise my HDL level? Lower my LDL?
It's harder to raise HDL than lower total cholesterol. Hormone replacement therapy can raise HDL in postmenopausal women, but it is no longer recommended for this purpose because it can increase the risk of breast cancer. Moderate alcohol consumption—up to one drink a day for a woman, two for a man—also helps boost HDL. Stop smoking if you smoke, lose weight if you are overweight and get regular aerobic exercise.To reduce LDL, limit your intake of saturated fat, trans fat and dietary cholesterol. Eat a diet rich in fruits, grains, vegetables and nonfat or low-fat dairy products. Cholesterol-lowering drugs primarily reduce LDL, but some also raise HDL.
I know my HDL and LDL. Why don't they add up to my total cholesterol?
Certain blood fats known as triglycerides also figure into the equation, which is:
Total cholesterol = HDL + LDL + (triglycerides ÷ 5)
In fact, LDL is not measured directly, but derived as follows:
LDL = total cholesterol - HDL - (triglycerides ÷ 5)
See the next question and answer for more information on triglycerides.
Are triglycerides also cholesterol? And is it important to pay attention to them?
It's important to know your triglyceride level and to lower it if it is elevated. Triglycerides are a type of fat that circulates in the blood and provides energy for the body. Triglycerides are also found in the fats we eat—and blood levels rise temporarily after meals. Excess calories are stored as triglycerides in fat tissue. Along with cholesterol, triglycerides tend to rise as people get older (and fatter). Women, especially after menopause, tend to have higher levels than men. Whether a high triglyceride level by itself endangers the heart is controversial. But high levels tend to go hand-in-hand with a constellation of other risk factors for heart disease, including low HDL cholesterol, increased levels of small dense particles of LDL cholesterol, insulin resistance or diabetes, abdominal obesity and high blood pressure. Treating these conditions often brings triglycerides down, too—though not always. If you have high triglycerides, dietary and lifestyle changes are usually the first steps. If these are insufficient, or if your levels are very high, you will need medical treatment.
Why don't package labels distinguish between good and bad cholesterol?
The cholesterol that we eat is simply cholesterol—you can't consume "good cholesterol." Dietary cholesterol comes only from animal products such as meats, poultry, fish, eggs and dairy products. The amount of cholesterol you consume affects the amount your body produces, which is also affected by genetic factors. But saturated fats, found chiefly in animal products, raise LDL more than dietary cholesterol does.
I've heard it's okay to eat eggs as well as shrimp. Both these foods are rich in cholesterol, so why are they okay?
It all depends on how much of these foods you eat and in what context—and what your personal risk factors are. One large egg contains about 185 milligrams of cholesterol; the American Heart Association recommends a daily maximum of 300 milligrams for most people (200 milligrams for those with heart disease, diabetes, or undesirable blood cholesterol levels). It would be okay to eat an egg if the other foods you eat that day are low in cholesterol.And some recent research suggests that eggs may actually provide some heart benefits. Shrimp contain more cholesterol than most shellfish (175 milligrams in 3 ounces)—but, like eggs, they are low in saturated fat, and shrimp, in moderate amounts, have a place in a heart-healthy diet.
Do I need to fast before a cholesterol test?
Although total cholesterol and HDL can be measured fairly accurately without fasting, to measure LDL and triglycerides (fats in the blood), you need to fast for 12 hours (overnight).
What can skew the results of a cholesterol test?
Fluctuations in weight shortly before the test, changes in diet and excessive alcohol intake can affect your test. So can surgery or injury, infection or severe physical strain. Your results may even vary with the seasons of the year. At test time, your weight should have been stable for at least two weeks, and you should have been eating your usual diet and drinking your usual amount of alcohol, if you drink at all. At least two weeks should have elapsed since any surgery, trauma, illness or physical strain.
Originally published January 2008. Updated May 2013.