Stearidonic acid: structure, properties and conversion to EPA

Chemical structure of stearidonic acid

Stearidonic acid or SDA (18 carbon atoms) is an essential polyunsaturated fatty acid or PUFA, with four cis (Z) double bounds (the first one from the methyl end is in n-3 or omega-3 (ω-3) so in shorthand 18:4n-3), member of the sub-group called long chain fatty acids (LCFAs), from 14 to 18 carbon atoms.

Properties of stearidonic acid

SDA: Molecular Structure
Fig. 1 – SDA

Molecular weight: 276.41372 g/mol
Molecular formula: C18H28O2
IUPAC name: (6Z,9Z,12Z,15Z)-octadeca-6,9,12,15-tetraenoic acid
CAS registry number: 20290-75-9
PubChem: 5312508

Other names of stearidonic acid

  • SDA
  • moroctic acid
  • cis-6,9,12,15-octadecatetraenoic acid
  • 6,9,12,15-octadecatetraenoic acid
  • (6Z,9Z,12Z,15Z)-octadecatetraenoic acid
  • all-cis-6,9,12,15-octadecatetraenoic acid
  • 6,9,12,15-octadecatetraenoate
  • 6,9,12,15-cis-octadecatetraenoic acid
  • 18:4n-3

Conversion of stearidonic acid to EPA and DHA

Synthesis of Stearidonic Acid
Fig. 2 – Synthesis of SDA

Stearidonic acid is produced de novo from apha-linolenic acid in a desaturation reaction catalyzed by the enzyme Δ6-desaturase, a reaction extremely inefficient in humans (as shown previously in rodents).
On the other hand, dietary and from de novo synthesis stearidonic acid is efficiently converted in eicosapentaenoic acid or EPA and docosapentaenoic acid or DPA by the subsequent actions of elongase (it catalyzes the addition of two carbon atoms from glucose metabolism to lengthen the fatty acid chain) and Δ5-desaturase and for this reasons its use may be a valuable tool for increasing EPA and docosahexaenoic acid or DHA tissue concentrations.
The further metabolism of stearidonic acid to DHA depends again on Δ6-desaturase (followed by a β-oxidation) and for this reasons this conversion is limited.

Sources of stearidonic acid

It occurs as glycerol ester in the leaf lipids of borage (Borago Offcianalis L., of the Boraginaceae) and in blackcurrant seed oil (3.5%) (Ribes nigrum, of the Saxifragaceae).


Akoh C.C. and Min D.B. “Food lipids: chemistry, nutrition, and biotechnology” 3th ed. 2008

Chow Ching K. “Fatty acids in foods and their health implication” 3th ed. 2008

James J.M., Ursin M.V., and Cleland G.L. Metabolism of stearidonic acid in human subjects: comparison with the metabolism of other n-3 fatty acids. Am J Clin Nutr 2003;77:1140-5 [Abstract]

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