Shark liver oil

Sharks typically targeted for their liver oil include the school and gulper shark, and the basking shark (pictured).[1] All three of these species have been assessed by the IUCN as Vulnerable due to overfishing.[2][3][4]

Shark liver oil is an oil obtained from the livers of sharks. It has been used for centuries as a folk remedy to promote the healing of wounds and as a remedy for respiratory tract and digestive system problems.[5][6] It is still promoted as a dietary supplement, and additional claims have been made that it can treat other maladies such as cancer, HIV, radiation illness, swine flu and the common cold.[5][7] To date, none of these claims has been medically validated and shark liver oil (alone) is not a medication prescribed or utilized by American physicians.[7] However, it is a component of some moisturizing skin lotions,[6] and some hemorrhoid medications.[8][9]

Function in the Shark

Many fish maintain buoyancy with swim bladders. However sharks lack swim bladders, and maintain their buoyancy instead with large livers that are full of oil.[10] This stored oil may also function as a nutrient when food is scarce.[11] Deep sea sharks are usually targeted for their oil, because the livers of these species can account for up to 20% of their total weight.[1]

Composition

A principal component of many shark oils is squalene, a triterpenoid (C30H50), ranging up to 90% of the oil, depending on the species. In Centrophorus species squalene may account for 15% of the total body weight. Pristane, another terpenoid (C19H40), is often a minor component, ranging up to nearly 8% of the oil.[12]

Medicinal use

Capsules containing shark liver oil.

Most shark liver oil supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Although many people have taken shark liver oil, the issue of potential toxicity at the usual doses has not been well studied. Some mild digestive problems such as nausea, upset stomach, and diarrhea have been reported. The safe range of doses for shark liver oil has not yet being determined, though overdosing can have toxic consequences.[5][13]

Some animal studies have found that shark liver oil and its components may raise blood cholesterol levels. A Japanese study found some shark liver oil supplements to be contaminated with polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs).[14] PCBs can have harmful effects in humans, and may increase the risk of some types of cancer.[5] People with seafood allergies may also react to shark liver oil.[5]

Shark liver oil has been misleadingly promoted as a treatment for cancer. Despite claims that the alkoxy-glycerols derived from shark liver oil could reduce tumor growth, there is not sufficient evidence to prove this to be a viable treatment option.[15]

Shark liver oil is listed as one of the principal active ingredients in hemorrhoid-control products such as Preparation H.

Shark oil barometers

Traditionally, Bermudians rely on unique shark-oil based "barometers" to predict storms and other severe weather. Small bottles of oil are hung outside.[16]

References

  1. 1 2 Vannuccini, Stefania (2002) Shark liver oil products In: Shark Utilization, Marketing and Trade, Fisheries Technical paper 389, FAO, Rome. ISBN 92-5-104361-2.
  2. ↑ Fowler (2005). "Cetorhinus maximus". IUCN Red List of Threatened Species. Version 2010.3. International Union for Conservation of Nature. Retrieved October 26, 2010.
  3. ↑ "Galeorhinus galeus (School shark)". Iucnredlist.org. 2005-06-17. Retrieved 2013-03-26.
  4. ↑ Guallart et al. (2006). Centrophorus granulosus. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 11 May 2006.
  5. 1 2 3 4 5 American Cancer Society. Retrieved 28 March 2013.
  6. 1 2 Gupta P, K Singhal, AK Jangra, V Nautiyal and A Pandey (2012) "Shark liver oil: A review" Asian Journal of Pharmaceutical Education and Research, 1 (2): 1-15.
  7. 1 2 Shark liver oil WebMD. Retrieved 28 March 2013.
  8. ↑ PE-shark liver oil-cocoa buttr Rect WebMD. Retrieved 28 March 2013.
  9. ↑ Hemorrhoidal suppository Daily Med. Retrieved 28 March 2013.
  10. ↑ Oguri, M (1990) "A review of selected physiological characteristics unique to elasmobranchs" In: Elasmobranchs as living resources: advances in the biology, ecology, systematics and the status of the fisheries, eds. J. H. L. Pratt, S. H. Gruber and T. Taniuchi, US Department of Commerce, NOAA technical report NMFS 90, pp.49–54.
  11. ↑ Bone Q and Roberts BL (1969) "The density of elasmobranchs" Journal of the Marine Biological Association, 49: 913–937.
  12. ↑ Ackman, RG. Marine Biogenic Lipids, Fats and Oils, Vol 1. CRC Press 1989, pages 42-43.
  13. ↑ S Kilincalp S, M Deveci, O Basar, F Ekiz, S Coban and O Yuksel (2012) Shark liver oil: hidden dangers" Annals of Hepatology, 11 (5): 728–730.
  14. ↑ Akutsu K, Tanaka Y, Hayakawa K (2006). "Occurrence of polybrominated diphenyl ethers and polychlorinated biphenyls in shark liver oil supplements". Food Addit. Contam. 23 (12): 1323–1329. doi:10.1080/02652030600892966. PMID 17118876.
  15. ↑ Sheldon Saul Hendler, David Rorvik, ed. (2008). PDR for Nutritional Supplements. Montvale, NJ: Physician's Desk Reference Inc. p. 22. ISBN 978-1-56363-710-0.
  16. ↑ Bermuda Traditions & Their Sources
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