gamma-Linolenic acid

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This article is about gamma-Linolenic acid. For α-Linolenic acid, see alpha-Linolenic acid. For linoleic acid (no "n"), see linoleic acid.
γ-Linolenic acid
Gamma linolenic acid spacefill.png
Gamma linolenic acid.png
IUPAC name
all-cis-6,9,12-octadecatrienoic acid
Other names
Gamma-linolenic acid, gamolenic acid, GLA
506-26-3 YesY
ChEBI CHEBI:28661 YesY
ChEMBL ChEMBL464982 YesY
ChemSpider 4444436 YesY
Jmol interactive 3D Image
PubChem 5280933
Molar mass 278.44 g·mol−1
Appearance Colorless oil
ATC code D11AX02
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY verify (what is YesYN ?)
Infobox references

Gamma-linolenic acid or GLA (γ-Linolenic acid), (INN and USAN gamolenic acid) is a fatty acid found primarily in vegetable oils. It is sold as a dietary supplement for a variety of human health problems with debated studies of evidence of its effectiveness.[1][2][3] However, when acting on GLA, 5-lipoxygenase produces no leukotrienes and the conversion by the enzyme of arachidonic acid to leukotrienes is inhibited.


GLA is categorized as an n−6 (also called ω−6 or omega-6) fatty acid, meaning that the first double bond on the methyl end (designated with n or ω) is the sixth bond. In physiological literature, GLA is designated as 18:3 (n−6). GLA is a carboxylic acid with an 18-carbon chain and three cis double bonds. It is an isomer of α-linolenic acid, which is a polyunsaturated n−3 (omega-3) fatty acid, found in rapeseed canola oil, soy beans, walnuts, flax seed (linseed oil), perilla, chia, and hemp seed.


GLA was first isolated from the seed oil of evening primrose. This herbal plant was grown by Native Americans to treat swelling in the body. In the 17th century, it was introduced to Europe and became a popular folk remedy, earning the name king's cure-all. in 1919, Heiduschka and Lüft extracted the oil from evening primrose seeds and described an unusual linolenic acid, which they name γ-. Later, the exact chemical structure was characterized by Riley.[4]

Although there are α- and γ- forms of linolenic acid, there is no β- form. One was once identified, but it turned out to be an artifact of the original analytical process.[5]

Dietary sources[edit]

GLA is obtained from vegetable oils such as evening primrose (Oenothera biennis) oil (EPO), blackcurrant seed oil, borage seed oil, and hemp seed oil. GLA is also found in varying amounts in edible hemp seeds, oats, barley,[6][full citation needed] and spirulina. Normal safflower (Carthamus tinctorius) oil does not contain GLA, but a genetically modified GLA safflower oil available in commercial quantities since 2011 contains 40% GLA.[7] Borage oil contains 20% GLA, evening primrose oil ranges from 8% to 10% GLA, and black-currant oil contains 15-20%.[8]

The human body produces GLA from linoleic acid (LA). This reaction is catalyzed by Δ6-desaturase (D6D), an enzyme that allows the creation of a double bond on the sixth carbon counting from the carboxyl terminus. LA is consumed sufficiently in most diets, from such abundant sources as cooking oils and meats. However, a lack of GLA can occur when there is a reduction of the efficiency of the D6D conversion (for instance, as people grow older or when there are specific dietary deficiencies) or in disease states wherein there is excessive consumption of GLA metabolites.[9][dubious ]

Source of eicosanoids[edit]

The seed oil of Oenothera biennis (evening primrose) is a source of GLA

From GLA, the body forms dihomo-γ-linolenic acid (DGLA). This is one of the body's three sources of eicosanoids (along with AA and EPA.) DGLA is the precursor of the prostaglandin PGH1, which in turn forms PGE1 and the thromboxane TXA1. Both PGE11 and TXA1 are anti-inflammatory; thromboxane TXA1, unlike its series-2 variant, induces vasodilation, and inhibits platelet[10] consequently, TXA1 modulates (reduces) the pro-inflammatory properties of the thromboxane TXA2. PGE1 has a role in regulation of immune system function and is used as the medicine alprostadil.

Unlike AA and EPA, DGLA cannot yield leukotrienes. However, it can inhibit the formation of pro-inflammatory leukotrienes from AA.[11]

Although GLA is an n−6 fatty acid, a type of acid that is, in general, pro-inflammatory, it has anti-inflammatory properties. (See discussion at Essential fatty acid interactions: The paradox of dietary GLA.)

Health and medicine[edit]

GLA has been promoted as medication for a variety of ailments including breast pain and eczema, in particular by David Horrobin (1939 – 2003), whose marketing of evening primrose oil was described by the British Medical Journal (BMJ) as ethically dubious – the substance was likely to be remembered as "a remedy for which there is no disease".[12] In 2002 the UK's Medicines and Healthcare products Regulatory Agency withdrew marketing authorisations for evening primrose oil as an eczema remedy.[13] Another single source suggests that Evening Primrose Oil with adjuvant vitamin E, may reduce breast pain.[14]

Side effects[edit]

Meta-analysis by the Cochrane Collaboration reported some evidence of mild and temporary side-effects for trial participants with either product or placebo, including temporary headache and upset stomach or diarrhoea. With evening primrose oil (EPO) there was an anticoagulant (blood-thinning) effect. There is a warning with the blood thinner warfarin that taking EPO can increase bleeding. One report[citation needed] warns that if EPO is taken for more than one year there is a potential risk of inflammation, thrombosis, and immunosuppression due to slow accumulation of EPO in the tissues. Another report[citation needed] involves a single case in which EPO was thought to have produced harm, but no clinical evidence of such harm was found in short-term trials.[1]

Notes and references[edit]

  1. ^ a b [References 1. Belch JJ, Hill A. Evening primrose oil and borage oil in rheumatologic conditions. Am J Clin Nutr. 2000 Jan;71(1 Suppl):352S-6S. 2. Bordoni A, Biagi PL, Masi M, et al. Evening primrose oil (Efamol) in the treatment of children with atopic eczema. Drugs Exp Clin Res. 1988;14(4):291-7. 3. Surette ME, Stull D, Lindemann J. The impact of a medical food containing gammalinolenic and eicosapentaenoic acids on asthma management and the quality of life of adult asthma patients. Curr Med Res Opin. 2008 Feb;24(2):559-67. 4. Leventhal LJ, Boyce EG, Zurier RB. Treatment of rheumatoid arthritis with gammalinolenic acid. Ann Intern Med. 1993 Nov 1;119(9):867-73. 5. Ishikawa T, Fujiyama Y, Igarashi O, et al. Effects of gammalinolenic acid on plasma lipoproteins and apolipoproteins. Atherosclerosis. 1989 Feb;75(2-3):95-104. 6. Schirmer MA, Phinney SD. Gamma-linolenate reduces weight regain in formerly obese humans. J Nutr. 2007 Jun;137(6):1430-5. 7. Das UN. A defect in the activity of Delta6 and Delta5 desaturases may be a factor predisposing to the development of insulin resistance syndrome. Prostaglandins Leukot Essent Fatty Acids. 2005 May;72(5):343-50. 8. Fearon KC, Falconer JS, Ross JA, et al. An open-label phase I/II dose escalation study of the treatment of pancreatic cancer using lithium gammalinolenate. Anticancer Res. 1996 Mar-Apr;16(2):867-74. 9. Li MC, Sun Y, Zhang Q, Xing LJ. Expression of delta6-fatty acid desaturase gene from Mortierella alpina in Pichia pastoris. Sheng Wu Gong Cheng Xue Bao. 2004 Jan;20(1):34-8. 10. Henz BM, Jablonska S, van de Kerkhof PC, et al. Double-blind, multicentre analysis of the efficacy of borage oil in patients with atopic eczema. Br J Dermatol. 1999 Apr;140(4):685-8. 11. Cameron M, Gagnier JJ, Little CV, Parsons TJ, Blumle A, Chrubasik S. Evidence of effectiveness of herbal medicinal products in the treatment of arthritis. Part 2: Rheumatoid arthritis. Phytother Res. 2009 Dec;23(12):1647-62. 12. Chilton FH, Rudel LL, Parks JS, Arm JP, Seeds MC. Mechanisms by which botanical lipids affect inflammatory disorders. Am J Clin Nutr. 2008 Feb;87(2):498S-503S. 13. Simopoulos AP. The omega-6/omega-3 fatty acid ratio, genetic variation, and cardiovascular disease. Asia Pac J Clin Nutr. 2008;17 Suppl 1:131-4. 14. Simopoulos AP. Evolutionary aspects of diet and essential fatty acids. World Rev Nutr Diet. 2001;88:18-27. 15. Fan YY, Chapkin RS. Importance of dietary gamma-linolenic acid in human health and nutrition. J Nutr. 1998 Sep;128(9):1411-4. 16. Stone KJ, Willis AL, Hart WM, Kirtland SJ, Kernoff PB, McNicol GP. The metabolism of dihomo-gamma-linolenic acid in man. Lipids. 1979 Feb;14(2):174-80. 17. Kapoor R, Huang YS. Gamma linolenic acid: an antiinflammatory omega-6 fatty acid. Curr Pharm Biotechnol. 2006 Dec;7(6):531-4. 18. Johnson MM, Swan DD, Surette ME, et al. Dietary supplementation with gamma-linolenic acid alters fatty acid content and eicosanoid production in healthy humans. J Nutr. 1997 Aug;127(8):1435-44. 19. Guivernau M, Meza N, Barja P, Roman O. Clinical and experimental study on the long-term effect of dietary gamma-linolenic acid on plasma lipids, platelet aggregation, thromboxane formation, and prostacyclin production. Prostaglandins Leukot Essent Fatty Acids. 1994 Nov;51(5):311-6. 20. Dobryniewski J, Szajda SD, Waszkiewicz N, Zwierz K. The gamma-linolenic acid (GLA)—the therapeutic value. Przegl Lek. 2007;64(2):100-2. 21. Ziboh VA, Naguwa S, Vang K, et al. Suppression of leukotriene B4 generation by ex-vivo neutrophils isolated from asthma patients on dietary supplementation with gammalinolenic acid-containing borage oil: possible implication in asthma. Clin Dev Immunol. 2004 Mar;11(1):13-21. 22. Chang CS, Sun HL, Lii CK, Chen HW, Chen PY, Liu KL. Gamma-linolenic acid inhibits inflammatory responses by regulating NF-kappaB and AP-1 activation in lipopolysaccharide-induced RAW 264.7 macrophages. Inflammation. 2010 Feb;33(1):46-57. 23. Hontecillas R, O’Shea M, Einerhand A, Diguardo M, Bassaganya-Riera J. Activation of PPAR gamma and alpha by punicic acid ameliorates glucose tolerance and suppresses obesity-related inflammation. J Am Coll Nutr. 2009 Apr;28(2):184-95. 24. Chaggar PS, Shaw SM, Williams SG. Review article: Thiazolidinediones and heart failure. Diab Vasc Dis Res. 2009 Jul;6(3):146-52. 25. Das UN. Can essential fatty acids reduce the burden of disease(s)? Lipids Health Dis. 2008;7:9. 26. Das UN. A defect in the activity of Delta6 and Delta5 desaturases may be a factor in the initiation and progression of atherosclerosis. Prostaglandins Leukot Essent Fatty Acids. 2007 May;76(5):251-68. 27. Das UN. Essential fatty acids and their metabolites could function as endogenous HMG-CoA reductase and ACE enzyme inhibitors, anti-arrhythmic, anti-hypertensive, anti-atherosclerotic, anti-inflammatory, cytoprotective, and cardioprotective molecules. Lipids Health Dis. 2008;7:37. 28. Belch JJ, Shaw B, O’Dowd A, et al. Evening primrose oil (Efamol) in the treatment of Raynaud’s phenomenon: a double blind study. Thromb Haemost. 1985 Aug 30;54(2):490-4. 29. Riaz A, Khan RA, Ahmed SP. Assessment of anticoagulant effect of evening primrose oil. Pak J Pharm Sci. 2009 Oct;22(4):355-9. 30. Shi LM, Ge HT, Kong XQ, et al. Effects of gamma linolenic acid on atherosclerosis induced by cholesterol-rich diet in rats. Zhongguo Zhong Yao Za Zhi. 2008 Dec;33(23):2808-12. 31. Fan YY, Ramos KS, Chapkin RS. Modulation of atherogenesis by dietary gamma-linolenic acid. Adv Exp Med Biol. 1999;469:485-91. 32. Fan YY, Ramos KS, Chapkin RS. Dietary gamma-linolenic acid suppresses aortic smooth muscle cell proliferation and modifies atherosclerotic lesions in apolipoprotein E knockout mice. J Nutr. 2001 Jun;131(6):1675-81. 33. Leng GC, Lee AJ, Fowkes FG, et al. Randomized controlled trial of gamma-linolenic acid and eicosapentaenoic acid in peripheral arterial disease. Clin Nutr. 1998 Dec;17(6):265-71. 34. Frenoux JM, Prost ED, Belleville JL, Prost JL. A polyunsaturated fatty acid diet lowers blood pressure and improves antioxidant status in spontaneously hypertensive rats. J Nutr. 2001 Jan;131(1):39-45. 35. Suresh Y, Das UN. Long-chain polyunsaturated fatty acids and chemically induced diabetes mellitus: effect of omega-6 fatty acids. Nutrition. 2003 Feb;19(2):93-114. 36. Pitel S, Raccah D, Gerbi A, Pieroni G, Vague P, Coste TC. At low doses, a gamma-linolenic acid-lipoic acid conjugate is more effective than docosahexaenoic acid-enriched phospholipids in preventing neuropathy in diabetic rats. J Nutr. 2007 Feb;137(2):368-72. 37. Shotton HR, Broadbent S, Lincoln J. Prevention and partial reversal of diabetes-induced changes in enteric nerves of the rat ileum by combined treatment with alpha-lipoic acid and evening primrose oil. Auton Neurosci. 2004 Mar 31;111(1):57-65. 38. Jamal GA, Carmichael H. The effect of gamma-linolenic acid on human diabetic peripheral neuropathy: a double-blind placebo-controlled trial. Diabet Med. 1990 May;7(4):319-23. 39. Horrobin DF. Essential fatty acids in the management of impaired nerve function in diabetes. Diabetes. 1997 Sep;46 Suppl 2:S90-3. 40. Keen H, Payan J, Allawi J, et al. Treatment of diabetic neuropathy with gamma-linolenic acid. The gamma-Linolenic Acid Multicenter Trial Group. Diabetes Care. 1993 Jan;16(1):8-15. 41. Arisaka M, Arisaka O, Yamashiro Y. Fatty acid and prostaglandin metabolism in children with diabetes mellitus. II. The effect of evening primrose oil supplementation on serum fatty acid and plasma prostaglandin levels. Prostaglandins Leukot Essent Fatty Acids. 1991 Jul;43(3):197-201. 42. Takahashi R, Inoue J, Ito H, Hibino H. Evening primrose oil and fish oil in non-insulin-dependent-diabetes. Prostaglandins Leukot Essent Fatty Acids. 1993 Aug;49(2):569-71. 43. Botha JH, Robinson KM, Ramchurren N, Norman RJ. The role of prostaglandins in the inhibition of cultured carcinoma cell growth produced by gamma-linolenic acid. Prostaglandins Leukot Essent Fatty Acids. 1989 Feb;35(2):119-23. 44. Purasiri P, Murray A, Richardson S, Heys SD, Horrobin D, Eremin O. Modulation of cytokine production in vivo by dietary essential fatty acids in patients with colorectal cancer. Clin Sci (Lond). 1994 Dec;87(6):711-7. 45. Pham H, Vang K, Ziboh VA. Dietary gamma-linolenate attenuates tumor growth in a rodent model of prostatic adenocarcinoma via suppression of elevated generation of PGE(2) and 5S-HETE. Prostaglandins Leukot Essent Fatty Acids. 2006 Apr;74(4):271-82. 46. de Bravo MG, Tournier H, Schinella G, Viaggi M, Quintans C. Effect of dietary supplementation with gamma-linolenic acid on the growth of a human lung carcinoma implanted in nude mice. Medicina (B Aires). 1995;55(6):670-4. 47. Hrelia S, Bordoni A, Biagi P, et al. gamma-Linolenic acid supplementation can affect cancer cell proliferation via modification of fatty acid composition. Biochem Biophys Res Commun. 1996 Aug 14;225(2):441-7. 48. Vartak S, Robbins ME, Spector AA. Polyunsaturated fatty acids increase the sensitivity of 36B10 rat astrocytoma cells to radiation-induced cell kill. Lipids. 1997 Mar;32(3):283-92. 49. Vartak S, McCaw R, Davis CS, Robbins ME, Spector AA. Gamma-linolenic acid (GLA) is cytotoxic to 36B10 malignant rat astrocytoma cells but not to ‘normal’ rat astrocytes. Br J Cancer. 1998 May;77(10):1612-20. 50. Das UN. Gamma-linolenic acid therapy of human glioma-a review of in vitro, in vivo, and clinical studies. Med Sci Monit. 2007 Jul;13(7):RA119-31. 51. Rahbeeni F, Hendrikse AS, Smuts CM, Gelderblom WC, Abel S, Blekkenhorst GH. The effect of evening primrose oil on the radiation response and blood flow of mouse normal and tumour tissue. Int J Radiat Biol. 2000 Jun;76(6):871-7. 52. Kairemo KJ, Jekunen AP, Korppi-Tommola ET, Pyrhonen SO. Effects of lithium gammalinolenate on the perfusion of liver and pancreatic tissues in pancreatic cancer. Anticancer Res. 1997 Sep-Oct;17(5B):3729-36. 53. Kenny FS, Pinder SE, Ellis IO, et al. Gamma linolenic acid with tamoxifen as primary therapy in breast cancer. Int J Cancer. 2000 Mar 1;85(5):643-8. 54. Ge H, Kong X, Shi L, Hou L, Liu Z, Li P. Gamma-linolenic acid induces apoptosis and lipid peroxidation in human chronic myelogenous leukemia K562 cells. Cell Biol Int. 2009 Mar;33(3):402-10. 55. Kong X, Ge H, Chen L, et al. Gamma-linolenic acid modulates the response of multidrug-resistant K562 leukemic cells to anticancer drugs. Toxicol In Vitro. 2009 Jun;23(4):634-9. 56. Miyake JA, Benadiba M, Colquhoun A. Gamma-linolenic acid inhibits both tumour cell cycle progression and angiogenesis in the orthotopic C6 glioma model through changes in VEGF, Flt1, ERK1/2, MMP2, cyclin D1, pRb, p53 and p27 protein expression. Lipids Health Dis. 2009;8:8. 57. Das UN. Nutrients, essential fatty acids and prostaglandins interact to augment immune responses and prevent genetic damage and cancer. Nutrition. 1989 Mar-Apr;5(2):106-10. 58. Booyens J, Maguire L, Katzeff IE. Dietary fats and cancer. Med Hypotheses. 1985 Aug;17(4):351-62. 59. Morse NL, Clough PM. A meta-analysis of randomized, placebo-controlled clinical trials of Efamol evening primrose oil in atopic eczema. Where do we go from here in light of more recent discoveries? Curr Pharm Biotechnol. 2006 Dec;7(6):503-24. 60. Kerscher MJ, Korting HC. Treatment of atopic eczema with evening primrose oil: rationale and clinical results. Clin Investig. 1992 Feb;70(2):167-71. 61. Businco L, Ioppi M, Morse NL, Nisini R, Wright S. Breast milk from mothers of children with newly developed atopic eczema has low levels of long chain polyunsaturated fatty acids. J Allergy Clin Immunol. 1993 Jun;91(6):1134-9. 62. Biagi PL, Bordoni A, Masi M, et al. A long-term study on the use of evening primrose oil (Efamol) in atopic children. Drugs Exp Clin Res. 1988;14(4):285-90. 63. Schalin-Karrila M, Mattila L, Jansen CT, Uotila P. Evening primrose oil in the treatment of atopic eczema: effect on clinical status, plasma phospholipid fatty acids and circulating blood prostaglandins. Br J Dermatol. 1987 Jul;117(1):11-9. 64. Morse PF, Horrobin DF, Manku MS, et al. Meta-analysis of placebo-controlled studies of the efficacy of Epogam in the treatment of atopic eczema. Relationship between plasma essential fatty acid changes and clinical response. Br J Dermatol. 1989 Jul;121(1):75-90. 65. Fiocchi A, Sala M, Signoroni P, Banderali G, Agostoni C, Riva E. The efficacy and safety of gamma-linolenic acid in the treatment of infantile atopic dermatitis. J Int Med Res. 1994 Jan-Feb;22(1):24-32. 66. Surette ME, Koumenis IL, Edens MB, et al. Inhibition of leukotriene biosynthesis by a novel dietary fatty acid formulation in patients with atopic asthma: a randomized, placebo-controlled, parallel-group, prospective trial. Clin Ther. 2003 Mar;25(3):972-9. 67. Lindemann J, David Pampe E, Peterkin JJ, Orozco-Cronin P, Belofsky G, Stull D. Clinical study of the effects on asthma-related QOL and asthma management of a medical food in adult asthma patients. Curr Med Res Opin. 2009 Dec;25(12):2865-75. 68. Belch JJ, Ansell D, Madhok R, O’Dowd A, Sturrock RD. Effects of altering dietary essential fatty acids on requirements for non-steroidal anti-inflammatory drugs in patients with rheumatoid arthritis: a double blind placebo controlled study. Ann Rheum Dis. 1988 Feb;47(2):96-104. 69. Brzeski M, Madhok R, Capell HA. Evening primrose oil in patients with rheumatoid arthritis and side-effects of non-steroidal anti-inflammatory drugs. Br J Rheumatol. 1991 Oct;30(5):370-2. 70. Zurier RB, Rossetti RG, Jacobson EW, et al. gamma-Linolenic acid treatment of rheumatoid arthritis. A randomized, placebo-controlled trial. Arthritis Rheum. 1996 Nov;39(11):1808-17. 71. Furse RK, Rossetti RG, Zurier RB. Gammalinolenic acid, an unsaturated fatty acid with anti-inflammatory properties, blocks amplification of IL-1 beta production by human monocytes. J Immunol. 2001 Jul 1;167(1):490-6. 72. Furse RK, Rossetti RG, Seiler CM, Zurier RB. Oral administration of gammalinolenic acid, an unsaturated fatty acid with anti-inflammatory properties, modulates interleukin-1beta production by human monocytes. J Clin Immunol. 2002 Mar;22(2):83-91. 73. Kast RE. Borage oil reduction of rheumatoid arthritis activity may be mediated by increased cAMP that suppresses tumor necrosis factor-alpha. Int Immunopharmacol. 2001 Nov;1(12):2197-9. 74. Soeken KL. Selected CAM therapies for arthritis-related pain: the evidence from systematic reviews. Clin J Pain. 2004 Jan-Feb;20(1):13-8.]. Conclusion: lack effect on eczema.
  2. ^ Cochrane Collaboration meta-analysis: Herbal therapy for treating rheumatoid arthritis. Conclusion: moderate evidence that oils containing GLA afford some benefit in relieving symptoms for RA. Many trials of herbal therapies are hampered by research design flaws and inadequate reporting.
  3. ^ Cochrane Collaboration meta-analysis: Polyunsaturated fatty acid supplementation for schizophrenia. Conclusion: Some studies show some improvement, but not statistically significant. Trials were small and short, most of the data they reported were not usable, and half of the trials were funded by the group supplying the trial medication.
  4. ^ Yung-Sheng Huang, Vincent A. Ziboh (2001). Gamma-Linolenic Acid: Recent Advances in Biotechnology and Clinical Applications. AOCS Press. p. 259. ISBN 1-893997-17-0. Retrieved 2007-12-07. 
  5. ^ Eckey, EW (1954). Vegetable Fats and Oils (volume 123 of American Chemical Society monograph series). Reinhold. p. 542. 
  6. ^ Qureshi AA, et al. (1984). Fed. Proc. 43: 2626.  Missing or empty |title= (help)
  7. ^ Nykiforuk, C.; Shewmaker, C. (19 August 2011). "High level accumulation of gamma linolenic acid in transgenic safflower (Carthamus tinctorius) seeds". Transgenic Research 21 (2): 367–81. doi:10.1007/s11248-011-9543-5. PMID 21853296. 
  8. ^ Flider, Frank J (May 2005). "GLA: Uses and New Sources" (PDF). INFORM 16 (5): 279–282. 
  9. ^ Horrobin DF (From the Efamol Research Institute. Kentville. Nova Scotia. Canada) (1993). "Fatty acid metabolism in health and disease: the role of delta-6-desaturase" (pdf). Am. J. Clin. Nutr. 57 (5 Suppl): 732S–736S; discussion 736S–737S. PMID 8386433. 
  10. ^ King, Michael W. "Introduction to the Eicosanoids". The Medical Biochemistry Page. 1996–2013, LLC. Retrieved 23 July 2013. 
  11. ^ Belch JJ, Hill A (2000). "Evening primrose oil and borage oil in rheumatologic conditions". Am. J. Clin. Nutr. 71 (1 Suppl): 352S–6S. PMID 10617996. Retrieved 2007-12-07. DGLA itself cannot be converted to LTs but can form a 15-hydroxyl derivative that blocks the transformation of arachidonic acid to LTs. Increasing DGLA intake may allow DGLA to act as a competitive inhibitor of 2-series PGs and 4-series LTs and, thus, suppress inflammation. 
  12. ^ Richmond, C. (2003). "David Horrobin". BMJ 326 (7394): 885. doi:10.1136/bmj.326.7394.885. 
  13. ^ Williams, H. C (2003). "Evening primrose oil for atopic dermatitis: Time To Say Goodnight". BMJ 327 (7428): 1358–9. doi:10.1136/bmj.327.7428.1358. JSTOR 25457999. PMC 292973. PMID 14670851. 
  14. ^ "Vitamin E and Evening Primrose Oil for Management of Cyclical Mastaglgia: A Randomized Pilot Study" (PDF). Alternative Medicine Review. Retrieved September 19, 2015.