A typical annual exam at a physician's office consists of many tests. Doctors check for healthy body weight, gauge general physical fitness and take tests, including blood pressure and blood work, a part of which is to test for cholesterol. The American Heart Association (AHA) sets forth recommendations and guidelines for healthy blood cholesterol, and notes that it is a marker for cardiovascular health and a potential indicator of an increased risk for heart disease.
Misconceptions
Many people think that, when it comes to cholesterol, less is better. In fact, this is not totally true. Cholesterol molecules are carried through the body by two types of transporters---LDL (low-density lipoprotein) and HDL (high-density lipoprotein). While the AHA recommends that LDL levels be kept as low possible, they conversely recommend that HDL levels be quite high.
Function
HDL moves cholesterol out of the body cells and toward the liver, explain biochemists Reginald Garrett and Charles Grisham. When cholesterol accumulates in the cells, it also accumulates in the bloodstream. From there, it can form plaque on the walls of arteries, which are blood vessels responsible for carrying blood from the heart to vital organs. This plaque can lead to atherosclerosis, or hardening of the arteries, which in turn represents a risk factor for heart attack and stroke. HDL, therefore, serves the function of reducing the risk of cardiovascular disease.
Considerations
While LDL levels are affected by diet, HDL levels are more determined by lifestyle. A 2000 study in the journal Circulation reports that moderate alcohol consumption (defined as one drink per day for women and two drinks per day for men) significantly increases HDL levels, with positive effects on cardiovascular health. Exercise, too, increases HDL, according to a 1987 study in the journal Metabolism.
Warning
Unfortunately, diet can affect HDL in one way---diets high in saturated and trans fat have been shown to negatively impact HDL, with detrimental effects on heart health. The mechanism by which saturated fat affects HDL is not completely understood, but some scientists hypothesize that these fats limit the transporter's ability to function. Trans fats, on the other hand, simply decrease levels of HDL, according to the AHA. For this reason, the AHA recommends limiting intake of trans and saturated fat.
Expert Insight
The AHA recommends that total cholesterol be lower than 200 mg/dL, but this recommendation is issued with the caveat that the total cholesterol is a modified sum of HDL and LDL (as well as triglycerides, another marker of heart health). Because high levels of HDL are associated with good health, it's more important to look at the HDL and LDL levels independently rather than total cholesterol in determining an individual's health status. The AHA recommends that HDL be at least 40 mg/dL, and ideally as high as (or even above) 60 mg/dL.
References
- "What Do My Cholesterol Levels Mean"; American Heart Association; 2007
- Biochemistry (journal); Reginald Garrett and Charles Grisham; 2007
- Circulation (journal); "Alcohol Consumption Raises HDL Cholesterol Levels by Increasing the Transport Rate of Apolipoproteins A-I and A-II"; E. Silva et al; 2000
- Metabolism (journal); "Exercise increases high density lipoprotein"; M. Kantor et al.; Feb 1987
- American Heart Association: Saturated and Trans Fat
