Shark liver oil (SLO) is the oil obtained from the livers of sharks, primarily Centrophorus squamosus, Cetorhinus maximus, and Squalus acanthias, or deep-sea shark, basking shark, and dogfish shark, respectively.

It has been long used in Scandinavian folk medicine to treat multiple ailments, including wounds, cancer, heart disease, and infertility (1).

Nowadays, it’s sold as a dietary supplement that promises to deliver these same health effects.

Research on SLO attributes its multiple health benefits to its high alkylglycerol (AKG), squalene, and omega-3 polyunsaturated fatty acid (PUFA) content (2).

The oil has a dark yellow to brown shade and pungent aroma and taste.

You may find SLO in liquid or capsule form, or as an ingredient in skin creams and lip balms.

Certain compounds in SLO, such as AKG, squalene, and omega-3 PUFAs, are thought to be responsible for its purported health benefits.

Here are some of SLO’s most popular uses and benefits that are backed by science.

May have anticancer properties

One of the most marketed benefits of SLO is its purported cancer-fighting potential, which is based on the extremely low incidence of cancer in sharks and supported by the oil’s high AKG and squalene contents.

AKG is a type of fat in blood-forming organs, such as bone marrow, the spleen, and liver. Aside from SLO, it’s also abundant in breastmilk and red blood cells (1, 3).

Test-tube and animal studies suggest that AKG may offer anti-tumor potential via activating macrophage and exerting anti-angiogenesis effects.

Macrophages are a type of white blood cell that digest defective cells, including cancerous cells, among other substances, and are considered fundamental in anti-tumor defense (1).

Meanwhile, an anti-angiogenesis effect means that it restricts the formation of new blood vessels that may feed cancer cells. Thus, it helps slow tumor growth and spread (1, 4).

What’s more, dogfish sharks are considered to be the richest source of squalene, a compound that got its name from this genus — Squalus (5).

Animal research shows that squalene may protect against chemically induced skin, colon, and lung cancer due to its antioxidant capacity, which fights the cancer-inducing effects of free radicals, as well as by interfering with the cancer-causing influence of certain substances (5).

Additionally, squalene is believed to reduce inflammation caused by anticancer drugs, making it a suitable add-on therapy during chemotherapy treatment (6).

However, keep in mind that human research is still needed.

May boost your immune system

Fishermen have also used SLO since ancient times due to its potential to enhance immunity.

Aside from activating macrophages, AKGs in the oil stimulate antibody production and enhance the function of Fc-receptors, which are proteins that contribute to the protective role of the immune system (1, 4).

For example, in one 4-week study in 40 older adults given 500 mg of pure AKG capsules twice daily before and after surgery, antibody levels significantly increased, inflammation slightly decreased, and the onset of complications was reduced (7).

On the other hand, squalene seems to work as an enhancer that improves vaccines’ effectiveness when mixed with surfactants — substances that allow the solubilization or stabilization of two compounds that otherwise wouldn’t blend.

This is most likely due to squalene’s immunostimulating activity, meaning that it stimulates antibody production and a stronger immune response (8).

Lastly, PUFAs, such as omega-3s found in SLO, may also influence your body’s immune function due to their anti-inflammatory effects (9).

May improve heart health

Another acclaimed benefit of SLO is its effect on heart health. However, scientific evidence regarding squalene is contradictory.

On one hand, studies attribute squalene with anti-atherosclerotic effects, meaning that it prevents or counteracts the buildup of plaque in your arteries, a risk factor for high blood pressure and stroke (10, 11).

Furthermore, squalene is a precursor to cholesterol production and believed to accumulate in the liver and lower cholesterol and triglyceride synthesis (11, 12, 13).

What’s more, one 11-week study in rats who were given 0.45 grams per pound (1 gram per kg) of squalene showed an increase in HDL (good) cholesterol levels (10).

Additionally, the omega-3 PUFAs present in the oil are known to reduce the risk of heart disease (14, 15).

On the other hand, further evidence suggests that squalene may increase total cholesterol and triglyceride levels (1, 4, 16).

In one study, animals fed a 0.05% and 0.5% squalene-supplemented diet showed 32% and 35% increases in total cholesterol levels, respectively. A similar trend was observed for blood triglyceride levels (1).

Similarly, another 4-week study in 13 adults determined that high doses of SLO, which contained 3.6 grams of AKG and squalene along with 750 mg of omega-3 PUFAs, increased total cholesterol levels by 23% (16).

An additional decrease in HDL (good) cholesterol levels was also noted, and researchers concluded that the anti-inflammatory effects of omega-3 don’t manifest with such high doses of AKG and squalene (16).

Similar results were found in healthy people when they supplemented with 15 grams per day of SLO for 4 weeks (4).

Other potential benefits

The AKGs, squalene, and omega-3 PUFAs in SLO may be responsible for the following additional health benefits:

  • May improve fertility. Animal studies show that the AKGs in SLO may improve sperm mobility and speed (1, 4).
  • May boost skin health. Squalene is a predominant component of skin oil or sebum. It provides skin hydration and protects it from ultraviolet (UV) damage (5, 17).
  • May prevent radiation sickness. AKGs in the oil significantly reduce injuries, such as tissue damage, caused by radiation therapy (1).
  • May reduce mouth ulcers. SLO may significantly reduce the appearance of recurrent mouth ulcers due to its beneficial effects on the immune system (1).

There are no known side effects of SLO.

However, as mentioned before, some controversy surrounds SLO’s effect on blood cholesterol levels, especially when consumed in high doses (1, 16).

Therefore, people with heart disease should avoid taking this supplement.

Additionally, older human and animal studies suggest that squalene derived from the oil may lead to SLO-induced pneumonia (18, 19, 20).

What’s more, liver injury was reported by one person who supplemented with two SLO capsules daily for 2 weeks, leading to toxic levels in the liver (21).

Thus, make sure to consult your healthcare provider before supplementing with SLO.

Lastly, though sharks are prone to heavy metal contamination — more specifically to mercury contamination — research suggests that it mostly accumulates in muscle tissue and fins (22).

An older study even suggests that when it comes to mercury-exposed fish, their oils tend to have negligible amounts of the metal, suggesting that it may be removed during the manufacturing process (23).

There’s little information on the appropriate SLO dosage or for how long to supplement with it. It’s said that intake needs may vary depending on users’ needs and preexisting conditions.

However, one study suggests that consuming 500 mg of SLO twice daily preoperatively may improve immunity and wound healing after surgery (7).

Still, keep in mind that adverse effects on blood cholesterol levels have been reported when consuming it at higher doses of about 15 grams per day (4).

While manufacturers recommend taking your SLO supplement with food to improve absorption, there’s no scientific evidence to back this claim.

Therefore, it’s best to follow your healthcare provider’s instructions regarding dosage, duration, and intake.

Despite its purported benefits for heart health, some studies suggest that a potential SLO overdose of 15 grams per day — or more — may increase blood cholesterol levels and lower HDL (good) cholesterol levels (1, 16).

These effects on blood cholesterol levels would be detrimental to your health and may counteract SLO’s anti-atherosclerotic effect, or its ability to prevent plaque buildup in your arteries.

There are no documented interactions between SLO and foods or drugs. Still, this doesn’t mean that they cannot occur.

For instance, SLO has a high omega-3 content, which is known to lower blood pressure. Thus, it may have an additive effect when taken together with blood-pressure-lowering drugs (24, 25).

Similarly, given the blood-thinning effect of omega-3 PUFAs, it’s believed that its intake may increase the risk of bleeding when combined with blood-thinning drugs like aspirin and warfarin. Nevertheless, scientific evidence is contradictory (26, 27, 28, 29, 30).

To avoid any such risks, be sure to consult your healthcare provider before taking SLO.

Due to its omega-3 PUFA content, SLO is highly prone to oxidation, meaning that it may easily become rancid.

Oxidized omega-3 supplements may lose their efficacy and lead to detrimental health effects (31).

Some factors that may cause your SLO supplement to lose its freshness include exposure to light, heat, and oxygen. Thus, some people recommend storing it in a dark place or even refrigerating it.

Most omega-3 supplements are safe for about 3 months after opening. Nevertheless, they may become rancid after 1 month, even when stored in the dark at 39°F (4°C) (31).

Hence, make sure to follow your supplement’s storage and handling directions.

Animal research has shown that orally supplementing with SLO during pregnancy increased white blood cell count in the offspring and mother’s colostrum — the first form of breast milk — suggesting a potential improvement in offspring immunity (4).

However, there’s no scientific evidence on the effect of SLO in pregnant and breastfeeding people, and thus, it should be avoided.

Aside from its potential adverse effects in people with heart disease and those taking blood-pressure-lowering and blood-thinning drugs, SLO may be generally safe for most people.

What’s more, SLO may be an alternative source of omega-3 for people with a fish allergy. This is due to the low allergenicity of cartilaginous fish like sharks among those who cannot tolerate bony fish (32, 33, 34).

While SLO is rich in AKGs, squalene, and omega-3 PUFAs — which are responsible for the majority of its health benefits — you may also find them in other food sources and supplements.

For instance, AKGs may also be found in cow’s milk and ratfish liver oil (1, 35).

As for squalene, you may also find it in reasonable amounts in olive, palm, wheat germ, amaranth, and rice bran oil (5).

Lastly, you may find omega-3 PUFAs in various animal and plant-based sources, including fatty fish, fish oil, chia seeds, flax seeds, and flaxseed oil (36, 37, 38).