Understand cholesterol and triglycerides, protect your cardiovascular system!

Author: Jia Mei, Chief Physician, Peking University People's Hospital

Reviewer: Jin Mei, Chief Physician, Beijing Anzhen Hospital, Capital Medical University

Blood lipids usually refer to indicators such as cholesterol, triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, apolipoproteins ApoA and ApoB, and lipoprotein (a) in plasma.

Increased blood lipids are closely related to atherosclerosis, especially low-density lipoprotein cholesterol which is deposited on the blood vessel walls to form lipid plaques. As the lipid core becomes larger and larger, the blood vessel walls become thinner and ruptured, and the plaques rupture, leading to thrombosis.

Figure 1 Original copyright image, no permission to reprint

If atherosclerotic plaque rupture occurs in the cardiovascular system, it is coronary heart disease; if it occurs in the cerebral blood vessels, it is stroke; if it occurs in the peripheral blood vessels, it is peripheral vasculitis.

Therefore, detecting these lipids and apolipoproteins in serum can be used to predict the risk of cardiovascular and cerebrovascular diseases.

1. Does consuming high-cholesterol and greasy food before blood drawing have any impact on blood lipids?

Although the cholesterol in the body mainly comes from its own synthesis, if you eat high-cholesterol foods for a long time, some of the cholesterol in the food will be absorbed into the blood. When the absorption exceeds the utilization and metabolism, it will lead to increased blood cholesterol.

In addition to diet, age and gender also have some impact on cholesterol. In addition, cholesterol testing is all done by glucose oxidase method. If vitamin C is taken for a long time or infused, it will cause a false decrease in cholesterol. If the sample is hemolyzed or jaundiced during the test, it will also cause a false decrease or increase in cholesterol.

If you eat too much greasy food the night before blood collection, the triglyceride test results will be abnormally high. This situation is very common. Experienced doctors will recommend a re-examination, requiring you to eat a light diet the night before blood collection and to have your blood drawn on an empty stomach the next morning for a re-examination.

Figure 2 Original copyright image, no permission to reprint

Triglycerides are exogenous fats that are ingested through the diet. Unlike cholesterol, most of which is synthesized by the body itself. If you eat roast duck or shabu-shabu the night before your blood is drawn, for example, your triglycerides will increase sharply the next day, and sometimes it may be chylosing.

The main reason for chylosing blood is eating very greasy food 1-3 days before blood collection, which leads to an abnormally high triglyceride concentration. The reference range of triglyceride concentration is below 1.7mmol/L. If it reaches 8mmol/L or 10mmol/L, the plasma will be the color of milk, so it is called chylosing blood.

If you eat particularly greasy food before blood draw, the doctor will tell you to be a vegetarian for three days and then come back for blood draw to be more accurate. Although there is a gap of three days, the difference in triglyceride values ​​between the two times is still quite large. The triglyceride index of the vegetarian night before is the standard. Of course, some patients are born with chylosing blood. No matter when blood is drawn, they will still have chylosing blood even if they eat vegetarian food.

2. What does increased or decreased cholesterol mean?

Total cholesterol refers to the sum of cholesterol contained in all lipoproteins in the blood, including free cholesterol and cholesterol esters. The vast majority of them are cholesterol esters bound to fatty acids, and less than 10% exists in a free state.

Increased cholesterol is related to coronary heart disease, diabetes, hypertension, nephrotic syndrome, hypothyroidism, smoking, drinking, etc.; decreased cholesterol is relatively rare in clinical practice, for example, liver disease, hyperthyroidism, anemia, severe infection, and malnutrition can cause decreased cholesterol.

Low-density lipoprotein combines with cholesterol to form low-density lipoprotein cholesterol. Low-density lipoprotein is synthesized by the liver or converted from very low-density lipoprotein. Increased levels of low-density lipoprotein are associated with atherosclerosis. Lowering low-density lipoprotein cholesterol is beneficial for preventing coronary heart disease and atherosclerosis, but the lower the better. Too low low-density lipoprotein levels can lead to cholesterol transport disorders and further malnutrition. It is enough to control it within an appropriate range.

Elevated LDL cholesterol can cause cerebrovascular and cardiovascular atherosclerosis, leading to cardiovascular and cerebrovascular events. Nephrotic syndrome, diabetes, and pregnancy can also cause elevated LDL cholesterol; malnutrition, chronic anemia, trauma, poor liver function, etc. can cause decreased LDL cholesterol.

High-density lipoprotein cholesterol is a combination of cholesterol and high-density lipoprotein. Because it has the highest density among lipoproteins, it is called high-density lipoprotein cholesterol.

High-density lipoprotein cholesterol is an indicator of anti-atherosclerosis and has a protective effect on blood vessels. High levels of high-density lipoprotein cholesterol reduce the risk of coronary heart disease, and the risk of coronary heart disease is negatively correlated with high-density lipoprotein cholesterol levels. Long-term exercise can increase high-density lipoprotein cholesterol, but some people who smoke or are obese will also have high high-density lipoprotein cholesterol.

Compared with low-density lipoprotein cholesterol, high-density lipoprotein cholesterol is a bad lipoprotein and high-density lipoprotein cholesterol is a good lipoprotein. In the past, it was believed that the higher the HDL cholesterol, the better, and it can protect the cardiovascular system. However, research in recent years has shown that HDL cholesterol also has subcomponents, and is divided into small particles and large particles. If there are more large particles of HDL cholesterol, it will protect against coronary heart disease, while small particles of HDL cholesterol have no protective effect on the cardiovascular system. Therefore, the more large particles of HDL cholesterol, the better, and high small particles of HDL cholesterol cannot reduce the risk of coronary heart disease.