Is it a joke to put some "oil" on your face? Cooking oil actually contains skin care ingredients!

In 1916, Japanese scientists first discovered an unsaponifiable substance in shark livers. This is a polyunsaturated triterpenoid compound named squalene. To date, deep-sea sharks are among the animals with the highest squalene content found in nature. Squalene accounts for more than 40% of shark liver oil [1], making it one of the main sources of squalene in the early days.

This phenomenon is not accidental.

For some animals that live in extreme environments, squalene may play a role similar to that of red blood cells in carrying oxygen . It captures oxygen in the body, transports it to the terminal cells of the body through the blood circulation, and then releases the oxygen, promoting the biological oxidation-reduction reaction in the body's metabolism, increasing the ability of tissue cells to utilize oxygen, and improving the tolerance of organisms to hypoxia, allowing sharks to survive in the dark, cold, high-pressure, and oxygen-deficient deep sea.

Coincidentally, on the other hand, in the Tibetan Plateau, where the air is thin, cold and the air pressure is low, people have found that yaks also have a high level of squalene.

Subsequently, squalene was extracted and studied from more animals and plants. People found that in addition to its oxygen-carrying capacity, squalene is also a substance with rich biological activity and is closely related to human health.

People who often eat olive oil may be familiar with squalene, which is another important oil companion in olive oil besides polyphenols.

Structurally, squalene is very similar to carotenoids (β-carotene and lycopene).

Structure determines properties. Just like β-carotene and lycopene, the presence of these six unsaturated bonds in squalene determines its active nature and the complex and diverse biological activities derived from it: anti-oxidation, lowering blood cholesterol, anti-tumor, etc.

In the body, squalene is also an important intermediate in the synthesis of endogenous cholesterol . Basically, most plants, animals, including humans, rely on squalene as an intermediate metabolite to synthesize cholesterol and other steroids. In plants, squalene cyclizes to form phytosterols, and in animals, squalene cyclizes to form cholesterol.

Sterol biosynthesis pathways in animals and plants | [2]

More interestingly, it is also one of the main components of human sebum, maintaining skin health by reducing oxidative damage to the skin caused by free radicals.

01

Unique presence in human sebum

Skin aging is the result of both internal and external factors. Among all external factors, photoaging is the number one culprit. The ultraviolet rays (UVA and UVB) in the sun can cause varying degrees of oxidative stress on the skin, leading to wrinkles, sagging and pigmentation.

The first line of defense against UV rays in the skin is a layer of sebum covering the surface of the skin. In addition to triglycerides, fatty acids, cholesterol, etc., sebum also contains squalene. As a highly effective antioxidant, squalene can block the chain reaction of free radicals, inhibit the peroxidation of sebum, play a photoprotective role, and prevent skin damage.

The content of squalene in sebum is about 12%. It is secreted by the sebaceous glands and is the place where squalene is most concentrated in the human body.

What’s amazing is that squalene is unique to human sebum and is not found in non-human primates, including apes that are closer to humans.

Perhaps this is also an evolutionary advantage. Faced with the potential threat of ultraviolet rays, monkeys have thick hair, while humans have squalene.

At this point, you might be wondering: Can I add more squalene to my sebum? After all, the more natural sunscreen, the better.

There are two ways, diet or application .

The first is diet. After being absorbed, squalene is transported through the blood circulation and distributed in various tissues of the human body. One of its main destinations is the skin, where it can reduce wrinkles, increase type I procollagen, and reduce UV-induced DNA damage to a certain extent.

The second step is to apply it. You may have found squalene in many skin care products. Yes, it can be partially absorbed by the skin. And squalene itself is also a good emollient that can help restore the softness and elasticity of the skin.

Based on current research, dietary supplementation with squalene is more effective .

Additionally, squalene appears to play an important role in retinal health, particularly in reducing free radical oxidative damage in rod photoreceptor cells[3].

Overall, consuming squalene-rich oils, such as extra virgin olive oil, in your diet can help keep your skin and eyes healthy.

02

Eating more will not increase bad cholesterol

As mentioned earlier, squalene can synthesize cholesterol. Will eating too much squalene increase blood lipids and cholesterol in the body, thereby increasing the risk of atherosclerosis?

No. Intake of exogenous squalene will not only not increase serum cholesterol levels, but can feedback regulate cholesterol, inhibit its endogenous synthesis and promote its excretion, and ultimately play a role in reducing the cholesterol content in serum.

Studies have shown that consuming 900 mg of squalene per day for 7-10 days can increase serum squalene concentrations by 17 times, but blood lipids and cholesterol do not change[3].

What does 900mg mean? Even residents in the Mediterranean region who eat olive oil every day consume less than 400mg of squalene per day.

In addition, the combined use of pravastatin and squalene in the treatment of patients with hypercholesterolemia can significantly reduce total cholesterol and LDL-C, and increase HDL-C. Moreover, the effect of the combined use of the two is significantly better than that of each alone. This is because the synthesis of cholesterol derived from the consumption of squalene increases the excretion of cholesterol in the form of fecal bile acid [4].

Patients with hypercholesterolemia were given pravastatin, squalene, or a combination of the two, and their blood lipid indexes were measured after 20 weeks. [4]

03

Reduced risk of cancer in Mediterranean populations

Although the composition of traditional diets varies among countries in the Mediterranean region, they all use olive oil as the main source of dietary lipids. A large number of public health studies have shown that the Mediterranean diet is not only associated with longevity, but also has a lower incidence of major chronic degenerative diseases such as cardiovascular disease and certain cancers [3].

One of the core elements of the Mediterranean diet is olive oil, and one of the core elements of olive oil is its oil companions. The main oil companions of olive oil, in addition to the familiar olive polyphenols, also include squalene, which cannot be ignored.

Statistics show that Mediterranean residents generally consume more squalene in their diet than those in other regions, with an average daily intake of 200-400 mg of squalene, while the intake in the United States is estimated to be only 30 mg .

It is this dietary pattern based on extra virgin olive oil rich in squalene that provides considerable protection for the local people[3].

According to research, squalene can reduce ROS levels in vitro and selectively protect normal human cells (breast epithelial cells) from oxidative DNA damage, but has no effect on bad cells (breast tumor cells).

We can more intuitively feel the protective effect of squalene on human breast epithelial cell DNA through a set of comet experiments. After squalene pretreatment, the tailing was significantly reduced, indicating that DNA damage was inhibited to a certain extent [3].

In addition, some animal experiments have also found that squalene's ability to scavenge free radicals or singlet oxygen can also resist radiation to a certain extent.

04

Olive oil and rice oil are the main sources

Squalene is widely distributed in vegetable oils, but except for a few vegetable oils with high content, the squalene content of most vegetable oils is less than 5% of the unsaponifiable matter. The squalene content of olive oil, rice oil and amaranth oil is relatively high.

Squalene content in different oils and fats (mg/100g) | [5]

In addition to choosing oils with high squalene content, it is also important to note that the squalene content of different products of the same cooking oil may vary greatly. This also depends on the processing technology.

The refining process of oils and fats will affect the content of squalene in the final oil product. For example, in the case of camellia oil, Chinese scientists have investigated the amount of squalene remaining in various stages of oil refining in a large-scale camellia oil refinery and found that the refining process causes a large loss of squalene[5].

Changes in squalene content of camellia oil during refining process | [5]

The higher the degree of refining, the less squalene residue there is. Moderate refining can retain these beneficial oil accompaniments to a greater extent and improve the nutritional value of edible oil.

This is the same as the processing of rice. The less polishing, the more the cortex is retained, and the higher the nutritional value. Brown rice that has not been polished or processed retains the most nutritional value. This is one of the reasons why the country strongly advocates moderate processing. As consumers, we should also develop the habit of checking nutrition labels frequently and choose products that retain more nutrients, are less processed, and are more beneficial to health.

References:

[1] Kim SK, Karadeniz F. Biological importance and applications of squalene and squalane. Adv Food Nutr Res. 2012;65:223-33.

[2] Micera M, et al. Squalene: More than a Step toward Sterols. Antioxidants (Basel). 2020 Aug 2;9(8):688.

[3]José J. et al. Chapter 26 - Molecular Aspects of Squalene and Implications for Olive Oil and the Mediterranean Diet. The Mediterranean Diet, Academic Press, 2015, Pages 281-290.
[4]Chan P, et al. Effectiveness and safety of low-dose pravstatin and squalene, alone and in combination, in elderly patients with hypercholesterolemia. J Clin Pharmacol. 1996 May; 36(5):422-7.
[5] Wang Xingguo, Jin Qingzhe, et al., “Theory and Practice of Precision and Moderate Processing of Edible Oil”.