HDL and LDL Explained (Made Easy to Understand)
Have high cholesterol or a family history of the same? Concerned about developing high cholesterol? Has your doctor ever talked to you about your cholesterol or asked you to check a lipid panel?
When someone talks about their “cholesterol levels”, what they are referring to (whether they know it or not) are lipoproteins, namely low density lipoprotein (or LDL) and high density lipoprotein (or HDL) as well as cholesterol and triglycerides. It’s important that you understand what these terms mean and why you should care, because they are important determinants of your health. This is a rather simplified summary for the curious, if you want a more detailed description, feel free to ask!
What are lipoproteins?
The way your body stores fat is very different from the dietary fat you ingest. The way your body manages fat storage is utilizing molecules collectively referred to as lipoproteins. As the name suggests, they contain both lipids (better known as fat) and proteins. This gives them both structure and function. Lipids normally don’t like water, that is to say they are hydrophobic, but attaching them to proteins makes them less hydrophobic. This allows us to move them around our body more effectively for various purposes. We are, after all, made up of about 60% water. So the purpose of lipoproteins is transportation of the things they contain.
There are two different general clusters of lipoproteins: High-density lipoproteins (HDL) and Low-density lipoproteins (LDL). HDL is what doctors and dieticians usually refer to as the ‘good cholesterol’ and the way I tell patients to remember that is the H in HDL stands for ‘healthy’. LDL is the ‘bad lipid’ and actually is the poster child for a spectrum of different lipoproteins such as IDL (intermediate), VLDL (very low) and chylomicrons. You won’t often hear people discussing anything besides HDL and LDL, but it is at least worth mentioning the others.
The purpose of these lipoproteins is to help deliver their contents to body tissues. Think of the liver as the ‘home base’ for these. LDL and it’s family transport their contents away from the liver to the tissues. HDL is for ‘reverse transport’; it’s responsibility is to bring things back to the liver for consumption and metabolism.
What do HDL and LDL contain?
These lipoproteins contain 4 different molecular classes. The first two I’ll mention briefly because they aren’t big players in this lecture.
First is Protein, which basically serve as part of the structure of the molecules as well receptors allowing these lipoproteins to talk to other cells. Second is phospholipids. These are lipids that serve as a major component of the cellular membrane. Of all the lipoproteins, HDL contains the most protein and phospholipids (which is where the term high-density comes from).
Cholesterol is the third component. Cholesterol has a complex molecular structure that is very similar to the various steroids that your body uses. It’s actually the precursor to many of the steroids and hormones that your body produces and uses as well as things like vitamin D and bile. It’s concentration is higher in LDL than HDL.
Triglycerides (or TAG) are the fourth molecule contained in these lipoproteins. The ‘tri’ aspect signifies the 3 fatty acid chains attached to the ‘glyceride’ backbone. Triglycerides are the major way your body stores dietary fat - such as saturated and unsaturated fats - as well as any fat that your body may produce. They can also be broken back down for energy when your blood glucose levels get low.
How do these lipoproteins affect your health?
The major concern with dyslipidemia (abnormal blood lipids) or hyperlipidemia (too high a lipid level) is atherosclerosis. Atherosclerosis is the process by which artery walls thicken from lipid plaque formation. These plaques can subsequently rupture, traveling through your arteries until they get stuck and stop blood flow, often leading to heart attacks and strokes.
- LDL: Higher blood levels correlate directly with increased risk for atherosclerosis and subsequent coronary heart disease. Higher levels are also strongly correlated to stroke risk.
- HDL: A low level correlates with an increased risk of atherosclerosis. In other words, normal and high HDL values are cardioprotective, reducing risk. Remember that HDL is the ‘healthy’ lipoprotein.
- Cholesterol: Increased cholesterol is associated with increased risk of atherosclerosis and cardiovascular events. You may see it presented as cholesterol to HDL ratio, but the relative interpretation is the same.
- Triglycerides: Increased triglycerides are an independent risk factor for coronary heart disease.
How can you improve your lipid profile?
A standard lipid profile from your doctors office will measure LDL, HDL, cholesterol and triglycerides as well as the ratio of some of them. Diet, exercise and weight loss have all been proven to improve parts or all of your lipid profile. This should be the standard recommendation of any provider.
- Diet: Avoid any foods containing trans fats or labeled as containing hydrogenated oil, for example avoid fried foods. Supplementing your diet with niacin, fish oil, and red yeast rice can help. The mediterranean and DASH diet have been shown to improve the lipid panel as well.
- Exercise: Exercise is shown to stimulate your bodies ability to remove bad cholesterol and to improve your good cholesterol.
- Weight Loss: Being overweight or obese is directly linked to risk of heart attack and stroke and weight loss alone has been shown to improve your lipid panel.
- Medications: Non-medication therapy can be inadequate to keep your levels in the appropriate range, so please consult with your primary care doctor if you have a history of abnormal lipid levels or a strong family history of the same.
The United States Preventative Services Tax Force (USPSTF) is a governing body of experts that examines the evidence on a given subject and makes recommendations about prevention of disease. They recommend screening all men over 35 and all women over 45 for dyslipidemia.
If you have a personal or family history that suggests other risk factors, you should consult your doctor and may need to be screened earlier. Target blood levels can vary depending on other risk factors and comorbid diseases, but as a general rule, the following target levels are recommended.
- Total Cholesterol: <200
- LDL: <100
- HDL: >60
- Triglycerides: <150