Cholesterol: the differences between HDL and LDL
Cholesterol and triglycerides are fats (lipids) naturally produced by our organism, which carry out fundamental roles in numerous processes:
- Cholesterol intervenes in the synthesis of vitamin D and other substances and contributes to keeping our cells stable and whole.
- Triglycerides are an important source of energy for our body.
A diet rich in foods of animal origin, with a high saturated fat content (like meat, butter, cold cuts, dairy products made from whole milk, cheese and eggs), foods high in trans fats (like margarine, cookies and potato chip), carbohydrates (pasta, bread and sugar) and alcohol can contribute to raising levels of these fats.
Cholesterol and triglycerides are insoluble in water, so they circulate in the form of substances known as lipoproteins.
What are lipoproteins?
We can think of lipoproteins as “containers” whose main purpose is to transport fats (which, by their nature, could not circulate freely in an aqueous medium) to various areas of the body.
Lipoproteins are complex particles, made up mostly of an internal nucleus composed of fats (triglycerides and cholesterol), surrounded by a membrane of phospholipids, free cholesterol and apolipoproteins.
These complexes intervene actively in the mechanisms of absorption and transport of nutritional fats from – and to the body’s peripheral tissues, as well as in the transport of toxic compounds (like some toxins produced by bacteria) away from infected areas.
Lipoproteins are classified according to their density: the greater their density, the lower the concentration of cholesterol they contain. Among the lipoproteins, the most important are:
- low-density lipoproteins (LDL), which transport cholesterol to various parts of the body;
- high-density lipoproteins (HDL), which are involved in removing excess cholesterol.
What is the difference between LDL and HDL cholesterol?
Not all cholesterol is bad for you: some types of cholesterol (like HDL) play an important role in keeping the organism healthy. So, let’s explain the differences between “good” and “bad” cholesterol:
LDL CHOLESTEROL – BAD FAT
When we talk about “bad cholesterol”, we are referring to LDL cholesterol, which accounts for the majority of the cholesterol present in our bodies.
This fat is defined “bad” because, when present in excess, it contributes to the accumulation of fat on the walls of our blood vessels, making them harden and blocking the flow; this increases the probability of developing some cardiovascular problems, like heart attacks and strokes.
We speak of “excess cholesterol” or “high cholesterol” when the levels of total cholesterol (obtained by summing “bad” LDL and “good” HDL cholesterol) rise above optimal values.
“Optimal” levels of total cholesterol should not be above 200 mg/dl, while the “optimal” levels of LDL cholesterol should not be above 100 mg/dl.
In diabetics and people who have had heart or kidney problems, values of LDL cholesterol should not be above 70 mg/dl.
HDL CHOLESTEROL – GOOD FAT
HDL cholesterol acts as a “garbage man”, freeing up the blood vessels and contributing to the elimination of between a quarter and a third of the LDL cholesterol in the bloodstream. This “good” fat helps protect the body from some illnesses, like heart attacks and strokes.
Various studies have found an inverse relationship between levels of circulating HDL and some heart diseases, regardless of LDL cholesterol levels:
- Low levels of HDL cholesterol (<40 mg/dl) are considered risky, regardless of the levels of LDL cholesterol;
- Values of HDL cholesterol >40 mg/dl for men and >48 mg/dl for women are instead indicators of low risk.
What factors influence levels of LDL and HDL cholesterol?
Cholesterol levels can be influenced by a variety of factors, among which:
- overweight or obesity,
- lack of physical activity,
It is not possible to intervene on some of these factors (age/sex and family medical history), while others can be modified by changing eating habits and lifestyle, among them the following:
- Diet – Levels of cholesterol and triglycerides in the bloodstream can increase due to an incorrect dietary regimen: a diet rich in foods containing saturated fats (like fatty meats, whole milk dairy products and tropical oils) contributes to increasing LDL cholesterol levels. Trans fats (found, for example, in some margarines used in baked goods), contribute to increasing levels of LDL cholesterol and reduce levels of good cholesterol. On the contrary, eating fruit and vegetables ensures a high intake of nutrients (vitamins and minerals), antioxidants (ex. polyphenols) with protective action and fiber, with fewer calories. Fruit, vegetables and, in particular, vegetable oils, contain plant sterols, which compete with cholesterol for intestinal absorption.
Vegetable oils (like extra virgin olive oil), rich in mono and polyunsaturated fats (ex. Omega-3 fatty acids), also help reduce the amount of saturated fat in your diet.
- Physical activity – physical activity not only helps you lose weight, but also to hold it steady. Engaging in regular physical activity (ca. 30 minutes a day) can help reduce levels of LDL cholesterol and increase those of HDL cholesterol.
- Overweight and obesity – the proportion of overweight and obese people is rising continuously. Losing weight can help lower LDL cholesterol levels. A healthy diet and plenty of physical activity from childhood on is an effective and necessary strategy for managing your weight. The Body Mass Index (BMI) is the parameter utilized to determine overweight and obesity. Waist circumference establishes abdominal obesity (correlated to the risk of cardiovascular illness).
Sometimes these modifications of your lifestyle may not be sufficient to keep your cholesterol levels within the desired limits; in these cases, your physician may suggest a pharmaceutical treatment using substances that reduce cholesterol levels (for example, statins).
How can you measure levels of HDL and LDL cholesterol?
High cholesterol does not manifest itself with specific symptoms, so it is advisable to check the levels of this fat periodically. To check whether you have high levels of circulating cholesterol, your doctor may prescribe a blood test that measures levels of HDL and LDL cholesterol.
The test that measures the concentration of cholesterol in plasma is called the “lipidic profile” and involves the calculation of a few parameters, specifically:
- Total cholesterol, or the sum of LDL and HDL cholesterol (values <200 mg/dl are considered “desirable”)
- HDL cholesterol (values <50 mg/dl are considered “desirable”)
- LDL cholesterol (values <100 mg/dl are considered “desirable”)
- triglycerides (values <150 mg/dl are considered “desirable”).
Another parameter evaluated by the lipidic profile test is “non-HDL” cholesterol, which, as its name suggests, is the result of subtracting HDL cholesterol from total cholesterol. To fall within a range defined as “healthy’, the concentration of non-HDL cholesterol should not be above 120-130 mg/dl.
In the case in which cholesterol levels do not fall within the range defined as “healthy’ for your age and sex, your doctor can suggest modifications in your lifestyle that will help to reduce or control high cholesterol, and may advise you to repeat the lipidic profile test.
- Istituto Superiore di Sanità – CUORE_Prevenzione e stili di vita – Colesterolemia. Disponibile al link: http://www.cuore.iss.it/prevenzione/colesterolo.asp. Ultimo accesso: Luglio 2019
- Zhang J, Li Q, Wu Y, et al. Cell Commun Signal. 2019;17(1):15.
- National Institute of Health- Your guide to lowering your cholesterol with TLC. Disponibile al link: https://www.nhlbi.nih.gov/files/docs/public/heart/chol_tlc.pdf. Ultimo accesso: Luglio 2019
- Feingold KR, Grunfeld C. Introduction to Lipids and Lipoproteins. [Updated 2018 Feb 2]. In: Feingold KR, Anawalt B, Boyce A, et al., editors. Endotext [Internet]. South Dartmouth (MA): MDText.com, Inc.; 2000-. Disponibile al link: https://www.ncbi.nlm.nih.gov/books/NBK305896/. Ultimo accesso: Luglio 2019
- Istituto Superiore di Sanità (ISS) – Epicentro: Colesterolo e ipercolesterolemia. Disponibile al link: http://www.epicentro.iss.it/colesterolo/ . Ultimo accesso: Luglio 2019
- Venugopal SK, Jialal I. Biochemistry, Low Density Lipoprotein – StatPearls – NCBI Bookshelf (Bookshelf ID: NBK500010).
- Elshourbagy NA, Meyers HV, Abdel-Meguid SS. Med Princ Pract. 2014;23(2):99-111.
- Centers for Disease Control and Prevention (CDC). LDL and HDL Cholesterol: “Bad” and “Good” Cholesterol. Disponible al link: https://www.cdc.gov/cholesterol/ldl_hdl.htm. Ultimo accesso: Luglio 2019
- ESC/EAS Guidelines for the Management of Dyslipidaemias. European Heart Journal. 2016;37: 2999–3058.
- American Heart Association (AHA). HDL (Good), LDL (Bad) Cholesterol and Triglycerides. Disponibile al link: https://www.heart.org/en/health-topics/cholesterol/hdl-good-ldl-bad-cholesterol-and-triglycerides. Ultimo accesso: Luglio 2019
- Istituto Superiore di Sanità – CUORE_Prevenzione e stili di vita. Disponibile al link: http://www.cuore.iss.it/prevenzione/colesterolo.asp. Ultimo accesso: Luglio 2019
- NIH – National Cholesterol Education Program- High Blood Cholesterol – What You Need to Know https://www.nhlbi.nih.gov/health-topics/all-publications-and-resources/high-blood-cholesterol-what-you-need-know. Ultimo accesso: Luglio 2019
- Ministero della Salute – direzione generale per l’igiene e la sicurezza degli alimenti e la nutrizione – Linee Guida Per La Prevenzione Dell’aterosclerosi. Sett 2004.
- NIH – NHLBI. High Blood Cholesterol. Disponibile al link: https://www.nhlbi.nih.gov/health-topics/high-blood-cholesterol. Ultimo accesso: Luglio 2019