HDL and LDL are commonly called the two types of cholesterol, where HDL is "good" cholesterol and LDL is "bad" cholesterol. While this isn't strictly accurate, you do certainly want as high a ratio of HDL to LDL as possible, since HDL helps protect the heart, and LDL increases your risk of heart disease.
Cholesterol in the Body
You may be under the impression, based upon what you've heard from various sources, that cholesterol is nothing more than a molecule that negatively impacts health. This isn't so, however. You actually depend upon having some cholesterol in your blood and in your cells to maintain health; without it, your cell membranes become too fluid, which decreases their strength. Further, you can't make vitamin D or the steroid hormones without cholesterol.
Too Much Cholesterol
While the right amount of cholesterol in the body is healthy, too much can build up in the arteries and lead to atherosclerosis, heart attack, and stroke. Since there's plenty of cholesterol and cholesterol generating fat in the American diet, almost no one is cholesterol deficient; most people have too much. For this reason, while cholesterol itself is important, things that increase cholesterol are commonly considered unhealthy.
HDL and LDL
LDL, or low-density lipoprotein, is not actually a kind of cholesterol; instead, it's a cholesterol transporter that carries cholesterol from the liver to the body cells, increasing the amount in your body, and increasing your risk of cardiovascular disease. HDL, or high-density lipoprotein, is a transporter that carries cholesterol out of the cells and back to the liver for excretion, reducing the amount in your body.
Ratio
Your level of LDL should be as low as possible, while HDL should be as high as possible. As such, though HDL to LDL ratio isn't commonly used as a measure of cardiovascular health, your HDL to LDL ratio should be as high as possible. Ideally, you want LDL to be less than 100 mg/dL to minimize risk. HDL should be higher than 60 mg/dL for optimal cardiovascular health.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- American Heart Association: Cholesterol
