Understanding Shark Liver Oil: Composition and History
Shark liver oil (SLO) is an oil extracted from the livers of various shark species, most notably deep-sea sharks like the dogfish and basking shark. Historically, Scandinavian fishermen used it as a folk remedy to treat a range of ailments, from skin conditions to respiratory problems. Today, it is marketed as a dietary supplement due to its high concentration of beneficial compounds, though the safety of consistent, long-term use is not well-documented. The key active ingredients in SLO are alkylglycerols (AKGs), squalene, and omega-3 fatty acids.
- Alkylglycerols (AKGs): These are a type of fat also found in lower levels in human bone marrow, breast milk, and spleen. They are believed to support immune function, though more robust human research is needed.
- Squalene: Named after the Squalus genus of sharks, squalene is a triterpene compound with antioxidant properties. It is a precursor to cholesterol synthesis in the body and is also widely used in cosmetics and vaccines.
- Omega-3 Fatty Acids: While SLO contains omega-3s, its concentration can be significantly lower than in other common marine oils, like fish oil. These fatty acids are well-known for supporting cardiovascular and brain health.
Documented Side Effects and Potential Risks
While some short-term studies have found shark liver oil to be well-tolerated, numerous case reports and animal studies raise significant concerns about its safety, especially with higher dosages or prolonged use. Potential health risks include:
- Gastrointestinal Issues: Mild digestive upset, such as nausea, diarrhea, and stomach discomfort, is the most commonly reported side effect, especially at larger doses.
- Elevated Cholesterol Levels: Multiple studies, including one in hamsters, found that shark liver oil and its squalene content can increase total cholesterol levels. This can be particularly concerning for individuals with pre-existing high cholesterol or heart disease, who may need to avoid this supplement.
- Hepatotoxicity (Liver Injury): A case study from 2012 documented severe acute toxic hepatitis in a patient who took shark liver oil capsules for just two weeks. While this is a rare occurrence, it highlights a serious potential risk of liver damage from this supplement.
- Risk of Contamination: As a marine product, SLO can be susceptible to contamination from environmental pollutants. Older studies have found some supplements to be contaminated with PCBs and heavy metals like mercury, which can accumulate in deep-sea sharks. Reputable third-party testing is crucial to mitigate this risk.
- Lipoid Pneumonia: Accidental inhalation of squalene, a primary component, has been linked to cases of lipoid pneumonia. While rare for oral consumption, it remains a serious risk, especially if capsules are broken or chewed.
High-Risk Groups Who Should Avoid Shark Liver Oil
Certain populations are particularly vulnerable to the potential risks associated with shark liver oil. It is strongly advised that these individuals avoid or use the supplement with extreme caution and only under a doctor's supervision.
- Pregnant and Breastfeeding Women: There is insufficient reliable information on the safety of SLO for pregnant or breastfeeding women. Due to the unknown effects and potential for contaminants, it is best to avoid use.
- Individuals with High Cholesterol: As shark liver oil may raise cholesterol levels, those with hypercholesterolemia or a history of cardiovascular disease should avoid it or use it only in moderation, as advised by a healthcare provider.
- People with Seafood Allergies: Individuals with a known allergy to seafood should be cautious, as a reaction to shark liver oil is possible.
- Patients Taking Certain Medications: Due to its omega-3 content, SLO may have a blood-thinning effect, potentially interacting with anticoagulant drugs like warfarin. It may also interact with immunosuppressants. Always consult a doctor if you are on medication.
- Individuals with Liver Disease: Given the documented case of liver toxicity, anyone with a history of liver issues should steer clear of shark liver oil.
Comparison of Shark Liver Oil vs. Cod Liver Oil
| Feature | Shark Liver Oil (SLO) | Cod Liver Oil (CLO) |
|---|---|---|
| Source | Deep-sea shark livers | Cod livers |
| Key Compounds | Alkylglycerols, Squalene | Omega-3s, Vitamin A, Vitamin D |
| Contamination Risk | Potential for heavy metals (mercury, PCBs) in unrefined versions | Generally low risk with reputable brands; regulated |
| Vitamin A Content | Variable; high levels in some supplements may risk toxicity | Standardized and controlled levels |
| Cholesterol Impact | May potentially increase cholesterol at high doses | Not typically known to increase cholesterol |
| Immunomodulation | Primary focus due to AKGs and Squalene | Secondary benefit due to anti-inflammatory properties |
| Established Use | Limited clinical evidence for many claims | Stronger evidence for general wellness, vitamins |
Conclusion: Making an Informed Decision
Is shark liver oil safe? For short-term use at recommended dosages from reputable manufacturers, it is considered possibly safe for most healthy adults, with mild digestive upset being the most common side effect. However, the lack of extensive, long-term human safety studies, coupled with reported cases of liver toxicity and potential contamination from pollutants, raises significant concerns. Furthermore, specific high-risk groups, including pregnant women and those with heart conditions or liver disease, should avoid it entirely. For many people seeking immune support or omega-3s, safer, better-researched alternatives like standard fish oil or plant-based sources of squalene may be more suitable. Always consult with a healthcare professional before starting any new supplement to ensure it is appropriate for your specific health needs.
Ethical Considerations
Beyond the human health risks, it is important to consider the ethical and environmental implications of consuming shark liver oil. Many of the deep-sea shark species targeted for their oil are endangered or critically endangered due to overfishing. Choosing ethically sourced or alternative supplements helps protect these vulnerable marine populations.
Key Safety Takeaways
- Short-Term Safety: Shark liver oil is likely safe for short-term use (e.g., up to 8 weeks) at recommended doses for healthy adults.
- Liver Risk: A documented case of severe toxic hepatitis highlights a rare but serious risk, meaning those with liver issues should avoid it.
- Contamination Concerns: Purchase only from reputable manufacturers who provide third-party testing to ensure the product is free of heavy metals and PCBs.
- Dosage Matters: High doses have been associated with digestive upset and potentially elevated cholesterol levels. Stick to recommended amounts.
- High-Risk Groups: Pregnant women, those with high cholesterol, and individuals on specific medications should avoid shark liver oil.
- Ethical Implications: The unsustainable harvesting of vulnerable shark species for their oil is a significant ethical concern.
- Alternative Options: Safer, more sustainable alternatives exist for obtaining alkylglycerols, squalene, and omega-3s.
Potential Side Effects
- Nausea and stomach upset
- Diarrhea
- Fishy aftertaste or burps
- Possible increase in cholesterol levels
- Risk of liver toxicity
- Potential for lipoid pneumonia from accidental inhalation
- Possible allergic reactions, especially in those sensitive to seafood
