HDL and LDL are colloquially called "good cholesterol" and "bad cholesterol" respectively. While high blood levels of HDL are associated with cardiovascular health, high levels of LDL are associated with risk of heart disease and other cardiovascular problems. Many behaviors that promote or increase HDL also lower LDL, though the effect each has on the other is not entirely clear.
Misconceptions
While it's quite common to say that HDL is "good cholesterol" and LDL is "bad cholesterol," in point of fact, there is only one kind of cholesterol--it's a biomolecule that is incorporated in identical form into both HDL and LDL. Explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry," HDL and LDL are actually cholesterol transporters. LDL, or low density lipoprotein, carries cholesterol away from the liver, while HDL, or high density lipoprotein, returns cholesterol to the liver.
Function
Understanding the relationship between HDL and LDL requires understanding what each of the transporter types does in the body. As Garrett and Grisham explain, LDL carries cholesterol to the body cells, which, if they need cholesterol, will take up LDL from the blood. If cells don't need cholesterol, they won't take up LDL, and levels increase in the blood. HDL returns excess cholesterol from the cells to the liver. In theory, then, the more HDL a person has, the lower their LDL should be, though in reality, the relationship can be more complex.
Dietary Considerations
Several dietary factors can affect HDL and LDL levels. Consumption of large amounts of saturated fat increases LDL, while consumption of trans fats increases LDL and decreases HDL. Unsaturated fats, which are the most heart-healthy of the three, according to Dr. Lauralee Sherwood in her book "Human Physiology," do not affect either LDL or HDL. As such, while it's possible to negatively impact both LDL and HDL through diet, it's not really possible to lower LDL and raise HDL through diet alone.
Lifestyle
Certain lifestyle factors can increase HDL and lower LDL. Daily consumption of moderate amounts of alcohol, such as 1 glass of wine or beer a day, appears to increase HDL concentrations and lower LDL concentrations. This is because alcohol impacts fat metabolism and affects the way the liver processes fats, say Mary Campbell and Shawn Farrell in their book "Biochemistry." Exercise can also increase HDL and lower LDL.
Expert Insight
The best cholesterol profile is one in which LDL is as low as possible and HDL is as high as possible. Because total cholesterol reflects the sum of both HDL and LDL--plus one-third of triglycerides--total cholesterol isn't necessarily a good indicator of cardiovascular health, notes the American Heart Association. Behaviors that increase HDL and lower LDL, whether independently of one another or in tandem, promote good heart health and decrease risk of heart disease.
References
- "Biochemistry"; Reginald Garrett and Charles Grisham; 2007
- "Human Physiology"; Lauralee Sherwood; 2004
- "Biochemistry"; Mary Campbell and Shawn Farrell; 2005
- American Heart Association: Cholesterol
