Cholesterol

In this Article (Index)

• What is Cholesterol?
• Types of Cholesterol
• Very Low-density lipoprotein (VLDL)
• Low-density lipoprotein (LDL)
• High-density lipoprotein (HDL)
• Cholesterol and the Brain
• Sources of Cholesterol
• Endogenous Cholesterol
• Dietary Cholesterol
• Is Cholesterol Linked to Heart Disease?
• Closing comments

What is Cholesterol?

French chemist Michel Eugène Chevreul (1786-1889) started studying animal fats in 1811, and while working on human gallstones, he discovered a substance that he named "cholesterine," now known as cholesterol.
The name comes from the Greek words chole = bile and stereos = soli), and the chemical suffix -ol for alcohol. It was first reported in human blood in 1833 by Félix-Henri Boudet (1806-1878).

Cholesterol is a waxy, fat-like compound that is an essential structural component of cell membranes and is a precursor molecule for vitamin D, sex hormones, and steroid hormones. The liver converts cholesterol into bile acids to excrete it from the body. It moves into the gut forming bile salt used in digestion for the absorption of fat-soluble vitamins A, D, E, and K. It also interacts with the gut microbiome which in turn modulates health and immune responses.

Types of Cholesterol

Lipoproteins are tiny ball-shaped particles with a core made up of fats (lipids) like cholesterol and triglycerides, an outer shell composed of phospholipids that surround the fat and allow it to be transported by the blood throughout the body (fat alone wouldn't do the job as fat and water -the blood- don't mix). Finally, the outer shell also contains special types of protein, called Apoproteins or apolipoproteins, that stabilize the blob and each variety gives it specific biochemical properties.

Lipoproteins come in different sizes, with differing mixes of fats and protein, and different properties. They have been classified into different groups, the most important ones are the following: (3)

Very Low-density lipoprotein (VLDL)

The largest in size, with a diameter of 30 to 90 nm (nanometers), and with a 90% lipid content they are the highest in fats, and triglyceride-rich with 55% of lipids being triglycerides, they contain the least cholesterol (24%), the balance is the emulsifying phospholipids. They have the lowest density of all lipoproteins. A Danish study using 25,480 individuals followed over 11 years showed that "VLDL cholesterol explained one-half of the myocardial infarction risk...[and] LDL cholesterol 29% of the risk of myocardial infarction." (4)

Low-density lipoprotein (LDL)

Known as "bad" cholesterol as it contributes to the buildup of fatty deposits, known as plaque, in arteries which can cause cardiovascular disease and death. (5)

Their size ranges from 20 to 25 nm, and have a 60% lipid content of which 24% is cholesterol and 12% triglycerides.

The good news is that certain foods can help reduce LDL cholesterol such as foods high in fiber like whole grains, including psyllium, oats, and barley (high in soluble fiber), healthy unsaturated oils (canola and 0live 0il), flaxseeds, almonds, avocados, tomatoes, turmeric, and green tea. On the other hand, unfiltered coffee and sugar can increase it. (8)

High-density lipoprotein (HDL)

It is often called "good" cholesterol because it counteracts the effects of LDL by promoting the transport of cholesterol to the liver for excretion. HDL also has antioxidant, anti-inflammatory, vasodilatory, and anti-blood clotting effects. (6)
They are the smallest, measuring 10 to 20 nm in diameter, and contain the lowest lipid level (60%) with the least amount of cholesterol (40%). Triglycerides make up 12% of their fat content.

Factors like a healthy diet (Mediterranean diet), eating fruits and vegetables rich in polyphenols (antioxidants), and regular physical activity enhance the beneficial effects of HDL, while smoking and chemical compounds known as obesogens impair its functions. (7)

Cholesterol and the Brain

The brain contains the highest concentration of cholesterol in the human body (20 to 25% of the total cholesterol). In contrast with other tissues, the brain does not uptake cholesterol from the blood, because this is prevented by the blood–brain barrier. Instead, it is synthesized by the brain by neurons and astrocytes.

Cholesterol plays an important role in the growth and development of nervous tissue and synaptogenesis, the formation of synapsis or connections between neural cells. A reduction in cholesterol levels can lead to loss of synapses and cause neurodegeneration.

Alterations in blood levels, and the distribution of cholesterol in the brain have been observed in Alzheimer's disease, Parkinson's disease, and Huntington's disease. Brain cholesterol also interacts with natural plant-based phytosterols that can cross the blood-brain barrier and accumulate there. The interplay of cholesterol and phytosterols plays a role in these diseases. Statins are used in medicine prescribed to lower LDL-cholesterol levels and reduce the risk of cardiovascular disease. However, the effects of statins on the development of dementia remain controversial as some studies suggest it may increase the risk of cognitive decline. (1),(2)

Sources of Cholesterol

Where does cholesterol come from? There are two sources: the cholesterol made by the body, and cholesterol in animal fats that make up our food.

Endogenous Cholesterol

Cholesterol is synthesized inside each nucleated cell in the human body. This is known as "endogenous" cholesterol (from the Greek words meaning "originating within"). The common belief that the liver produces most of the cholesterol is not true: it only produces between 10 to 20% of it.

However, the liver is where cholesterol is broken down in a process called catabolism, and excreted. The blood transports from the body's tissues to the liver for its disposal. This is roughly 9 mg of cholesterol per kilogram of body weight that moves daily into the liver to be catabolized.

Dietary Cholesterol

The body also uptakes cholesterol from certain foods such as animal fat found in meat, fish, dairy products, and eggs. Vegans and vegetarians have a much lower cholesterol intake than those eating a typical omnivore diet because plant-based foods do not contain cholesterol. However, despite consuming 90% less cholesterol from food sources, their LDL cholesterol levels are only 13% lower than omnivores. This shows how the body maintains a balance of circulating cholesterol, compensating drops in dietary cholesterol with an increased output of endogenous cholesterol.

Is Cholesterol Linked to Heart Disease?

Dietary cholesterol has been suggested to increase the risk of cardiovascular disease (CVD) and for this reason, the U.S. Dietary Guidelines (2010) recommends a cholesterol "level of less than 300 mg per day," adding that " Consuming less than 300 mg per day of cholesterol can help maintain normal blood cholesterol levels. Consuming less than 200 mg per day can further help individuals at high risk of cardiovascular disease."

Previously there was no recommended dietary daily allowance for cholesterol (9), however, the Food and Drug Administration (FDA) set a daily value of less than 300 mg per day, a figure that was also adopted by the American Heart Association.

But recent research has questioned this link between dietary cholesterol and cardiovascular disease suggesting that it is based on poorly designed studies and trials.

Furthermore, taking dietary cholesterol isolated from its context and placing the blame for CVD on it is a mistake. Research has shown that eating excessive quantities of saturated fat, with too much sugar, and sodium, and not eating enough plant-based fiber are factors that increase the risk of heart disease.
For this reason the most recent U.S. Dietary Guidelines (2020-2025) have dropped the strict figure of 300 mg per day, and instead, recommend "that ... dietary cholesterol consumption to be as low as possible."

Cholesterol in food is not to blame

There are many studies that refute the direct correlation between dietary cholesterol and blood cholesterol levels; we will mention some of them in this section.

A meta-analysis of 40 studies covering 361,923 subjects and 19 trials with 632 subjects (10) revealed that:

Dietary cholesterol was not statistically significantly associated with any coronary artery disease, ischemic stroke, or hemorrhagic stroke... Reviewed studies were heterogeneous and lacked the methodologic rigor to draw any conclusions regarding the effects of dietary cholesterol on CVD risk. Berger S, Raman G, Vishwanathan R, Jacques PF, Johnson EJ., (2015)

This analysis did find that dietary cholesterol increased total cholesterol, LDL, and HDL blood-levels, but didn't change triglycerides or VLDL concentrations.

Another review of data on cholesterol reported that "there is not a direct correlation between cholesterol intake and blood cholesterol" (11)

This study suggests that the body's compensatory mechanisms take care of excessive dietary cholesterol by lowering endogenous cholesterol output.

Clinical interventions in the last 20 years demonstrate that challenges with dietary cholesterol do not increase the biomarkers associated with heart disease risk. Fernandez ML, Murillo AG., (2022)

They also placed the blame on other factors that usually accompany cholesterol such as saturated and trans fats associated with the Western diet.

This finding was also observed in a study study that followed 8,095 participants for an average of 11.4 years (12) and found that eggs, which are blamed for high cholesterol levels may actually reduce CVD mortality and exert a protective effect through their anti-inflammatory properties. This study mentions that this effect "is not found in other cholesterol sources such as red meat, pork, cheese or butter, which also have a substantial amount of saturated fat, a nutrient positively linked to CVD."

A Japanese study suggests that instead of focusing on dietary cholesterol, the scope should involve all foods consumed and places the blame for CVD on the Western diet: "an optimal intake of whole grains, vegetables, fruits, nuts, legumes, dairy, fish, red and processed meat, eggs, and sugar-sweetened beverages showed an important lower risk of CHD, stroke, and heart failure." (13)

A Healthy Diet

The American Heart Association (14) also found that current scientific evidence does support a link between dietary cholesterol and cardiovascular disease, and it concluded that healthy dietary patterns like the Mediterranean diet and the DASH [Dietary Approaches to Stop Hypertension] are a better option to promote heart health. These diets rich in "fruits, vegetables, whole grains, low-fat or fat-free dairy products, lean protein sources, nuts, seeds, and liquid vegetable oils... [are] more likely to improve diet quality and to promote cardiovascular health."

Closing Comments and More Cholesterol Resources

There are plenty of resources on our website about Cholesterol, health, and healthy food.
Don't miss our pages on Ultra-processed foods, and the Health Risks of Ultra-processed-foods-
Learn if Saturated Fats are good or bad for you, and all about a Healthy Eating Plan and a Balanced diet.

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