Is cholesterol really a "health killer"? Let's hear what it says

Author: Pan Yujie (Shanghai Center for Plant Stress Biology, Chinese Academy of Sciences)

The article comes from the Science Academy official account (ID: kexuedayuan)

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Dear readers and friends:

Hello everyone!

I am cholesterol. I believe everyone is familiar with me. Over the years, everyone likes to call me the "health killer" and avoids talking about me. In fact, I am really wronged. Like protein and vitamins, I am an indispensable substance for the body. Today, I decided to let everyone get closer to me and truly understand me through this self-introduction letter.

Let’s get to know me first

In addition to "cholesterol", you can also call me cholesterol. I am a derivative of cyclopentane polyhydrophenanthrene, insoluble in water and blood. As early as the 18th century, people had discovered me from gallstones. In 1816, the chemist Bencher gave me a nice and loud name - cholesterol!

Figure 1 Chemical formula of cholesterol (Source: Wikipedia)

I am widely present in the animal body, especially in the brain and nerve tissue, and also in high concentrations in the kidneys, spleen, skin, liver and bile.

In animal tissue cells, I am not only involved in the formation of cell membranes (Figure 2), but also a precursor molecule for several biochemical pathways. For example, I am a precursor molecule for the synthesis of vitamin D and all steroid hormones, including adrenal hormones cortisol and aldosterone, as well as sex hormones progesterone, estrogen and testosterone and their derivatives. So I am not only not a substance harmful to the human body, but also indispensable to the body!

Figure 2 Cholesterol participates in the formation of cell membranes

In adults, cholesterol can be synthesized in various tissues except brain tissue. The liver and intestinal mucosa are the main sites of synthesis. 70-80% of the cholesterol in the body is synthesized by the liver and 10% by the small intestine. The liver excretes cholesterol into bile, which is then stored in the gallbladder[1][2][3].

Many people mistakenly think that I am fat, especially girls who like slim figures, who avoid me like a scourge. However, it is time to pay attention! Lipids are a general term for oils, fats, and lipids. Fat is a triglyceride composed of glycerol and fatty acids, and I belong to a member of lipids. Lipids, as the name suggests, means "similar to fat". So, although I have many similarities with fat and belong to the same lipid, our structure and function are different! Moreover, there is no direct relationship between high cholesterol and obesity. High cholesterol is not exclusive to fat people, thin people can also have it! However, consuming too much high-fat food and lack of exercise are one of the common causes of high cholesterol and obesity.

Why did I get labeled as a “health killer”?

Some people may ask, since you have so many important functions in the body, why do people call you a "health killer"? In fact, it's the fault of the transportation I took!

In the blood, there are some lipoproteins that are responsible for transporting lipids. They carry me to various places in the human body. The core component of lipoprotein is triglyceride, which is surrounded by a layer of phospholipids, cholesterol, and protein molecules. Lipoproteins can be divided into chylomicrons (CM), very low-density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL) according to their density. The latter two are closely related to me.

●High-density lipoprotein (HDL): Mainly synthesized by the liver, it is composed of phospholipids, apolipoproteins, cholesterol and a small amount of fatty acids. High-density lipoprotein helps to remove cholesterol from cells. Arterial angiography has shown that the content of high-density lipoprotein cholesterol (HDL-c) is significantly negatively correlated with the degree of arterial lumen stenosis. It is a protective factor for coronary heart disease, commonly known as the "vascular scavenger". Because of the team's awesomeness, people like to call me "good cholesterol" at this time. The ratio of total cholesterol to high-density lipoprotein is preferably less than 4.5 for men and less than 3.5 for women. The lower the ratio of total cholesterol to high-density lipoprotein, the healthier the cardiovascular and cerebrovascular system. Researchers also found that not smoking, drinking a little alcohol and doing physical exercise several times a week to improve heart function are the three keys to increasing the amount of HDL-c in the human body!

● Low-density lipoprotein (LDL): It carries cholesterol into peripheral tissue cells. When the content of oxidized low-density lipoprotein (OX-LDL) is too high, the cholesterol it carries will be deposited on the walls of blood vessels and arteries, which can easily cause arteriosclerosis over time[4]. As the amount of deposits increases, the blood vessels gradually narrow, causing cardiovascular and cerebrovascular diseases such as coronary heart disease or stroke. What is more dangerous is that if unstable plaques rupture or blood clots fall off, blood vessels will be blocked in a short period of time, leading to cerebral infarction or acute myocardial infarction, which is life-threatening[5].

Low-density cholesterol (LDL-c) is the cholesterol in LDL, which reflects the amount of low-density lipoprotein. At this time, I am called "bad cholesterol", which is why people call me "health killer". Therefore, everyone should keep LDL-c at the normal value of 105-130mg/dl. Controlling the increase of LDL-c can significantly reduce the risk of stroke, cardiovascular events and total death.

Figure 3 LDL causes the progression of atherosclerosis and blocks the arterial lumen (Wikipedia)

How to be good friends with me?

In life, why do some people develop cardiovascular diseases when eating high-cholesterol foods, while some hateful people eat them happily and still remain healthy?

In fact, I undergo a very complex synthesis process in the body, and it is not determined solely by the food you take in. Research shows that I levels in the body are mainly regulated by two aspects, one is diet and lifestyle, and the other is affected by genetic factors.

· Diet and lifestyle: Many people will ask, is high cholesterol caused by eating foods high in cholesterol? Not entirely. In fact, cholesterol mainly comes from the body's own synthesis (endogenous cholesterol), and food sources are my secondary supplement (exogenous cholesterol).

Let's take an adult with a body weight of 70kg as an example. There are about 140g of cholesterol in the body, and about 1g is renewed every day. About 1/5 of it is supplemented from food, and the rest is produced by metabolism in the body. In fact, about 200mg of cholesterol per person per day from food can meet the normal needs of the body. The absorption rate of cholesterol in the body is about 30%, and it will decrease as the intake of cholesterol increases. How much is 200mg of cholesterol? It is roughly equivalent to the cholesterol contained in 1 egg, or the cholesterol absorption of 3 to 4 eggs.

Figure 4 Dietary cholesterol is not the only source of blood cholesterol

Just now I told you about the harm of LDL-c. There are many factors that cause high LDL-c, which are mainly divided into two categories: non-pathological factors and pathological factors. Among them, non-pathological factors include unbalanced diet, high cholesterol intake, smoking and drinking, overweight and obesity. So let's get to know some low-cholesterol foods that are safe to eat (cholesterol content per 100 grams of food is less than 100 mg), such as eel, pomfret, carp, lean pork, lean beef, lean lamb, duck, etc.; and the following high-cholesterol foods (cholesterol content per 100 grams of food is 200-300 mg) should not be eaten too much: such as pig kidney, pig liver, pig stomach, mussel meat, pig fat, egg yolk, crab roe, etc. Experts recommend that it is best to consume 50mg~300mg of cholesterol per day, so for your health, please control your mouth and move your legs!

Genetic factors: I recently heard a very interesting scientific research result. The research from Song Baoliang's research group at the School of Life Sciences of Wuhan University and Ma Yitong's team at Xinjiang Medical University told us that some people actually have cholesterol-lowering genes. Are you envious? Through epidemiological surveys, they found a Kazakh family that was born with very low LDL-c levels!

As shown in Figure 5, the half-full squares and circles represent individuals with lower LDL-C levels (squares and circles represent males and females, respectively). The numbers below show the LDL-C concentration (mmol/L) of each member. The normal range of LDL-C concentration is 2.7 to 3.1 mmol/L. Their LDL-C concentration is significantly lower than the normal value, even 1/3 of the normal value!

Figure 5 The LIMA1 gene mutation LIMA1-K306fs is associated with low plasma LDL-c levels [6]

Scientists have discovered that their LIMA1 gene has mutated, which can reduce the absorption of cholesterol in the small intestine and reduce the LDL-c level in human plasma! This suggests that LIMA1 can be used as a new target for the development of cholesterol-lowering drugs, and helps us understand why the Kazakhs, although they consume more beef and mutton, have a lower incidence of cardiovascular and cerebrovascular diseases than the Han population [6]. The related work was published online in the journal Science under the title A LIMA1 variant promotes low plasma LDL cholesterol and decreases intestinal cholesterol absorption.

Conclusion

Well, the above is my self-introduction, I hope you can understand me scientifically. Although wine is good, don't drink too much; although I am useful, don't be greedy.

High cholesterol is certainly not good for the body, but too low cholesterol can also affect health. For example, the stability of cell membranes is weakened, leading to increased fragility of blood vessel walls. Too low levels of raw materials for the synthesis of hormones such as corticosteroids, progesterone, androgens, and estrogens can affect the normal synthesis of these hormones in the body, leading to weakened stress resistance, weakened immunity, and affecting normal sexual function.

Therefore, I hope that I can work hard to maintain normal levels in your body and contribute to your health!

Best wishes

Still Love Your Cholesterol

References:

1. Hanukoglu I (Dec 1992). "Steroidogenic enzymes: structure, function, and role in regulation of steroid hormone biosynthesis". J Steroid Biochem Mol Biol. 43 (8): 779–804. doi:10.1016/0960-0760(92)90307-5. PMID 22217824.

2. Payne AH, Hales DB (2004). "Overview of steroidogenic enzymes in the pathway from cholesterol to active steroid hormones". Endocrine Reviews. 25 (6): 947–70. doi:10.1210/er.2003-0030. PMID 15583024.

3. "Secretion of Bile and the Role of Bile Acids In Digestion". www.vivo. colostate.edu. Retrieved 2018-04-09.

4. Glagov, Seymour; Weisenberg, Elliot; Zarins, Christopher K.; Stankunavicius, Regina; Kolettis, George J. (28 May 1987). "Compensatory Enlargement of Human Atherosclerotic Coronary Arteries". N. Engl. J. Med. 316 (22): 1371–1375.

5. Scientific statement on the correct understanding of cholesterol. Chin J Prev Med. November 2016, Vol,50.No.11.

6.Ying-Yu Zhang, Zhen-Yan Fu, Jian Wei, et al. A LIMA1 variant promotes low plasma LDL cholesterol and decreases intestinal cholesterol absorption. Science. 2018, 360 (6393): 1087.