What Are the EPA & the DHA Made From?

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are long-chain polyunsaturated fatty acids (PUFA), which are fatty acids containing 18 or more carbon atoms and two or more double bonds. Dietary sources of EPA and DHA are fish liver or fish flesh. EPA and DHA have functions in cell metabolism and are associated with prevention of cardiovascular diseases and obesity. DHA is also linked to visual and brain development in infants. Both are made from the same compound, alpha-linolenic acid (ALA), via bio-synthetic pathways.

Structure and Classification

• EPA has 20 carbon atoms and five double bonds, while DHA has 22 carbon atoms and six double bonds. EPA and DHA are classified as n-3 PUFAs or omega-3 fatty acids, as the double bonds in both compounds begin from the third carbon atom. ALA is the precursor to EPA and DHA and is found only in plant sources, and thus is categorized as an essential fatty acid (EFA) because it cannot be synthesized by the human body.

EPA Bio-synthesis

• EPA bio-synthesis occurs via an array of reactions involving the addition of double bonds and carbon atoms, called desaturation and elongation respectively. ALA has 18 carbon atoms and three double bonds and is desaturated to form octadecatetraenoic acid (OTA), containing four double bonds. OTA is elongated to form eicosatetraenoic acid, which contains 20 carbon atoms. A final desaturation step produces EPA.

EPA Bio-synthesis -- Alternative Pathway

• EPA is also synthesized via an alternative pathway. This process is mainly utilized when the regular pathway is blocked by disease, and was found occurring in human testis and breast cancer cells. The key difference between both pathways occurs in the first step, where ALA is elongated to 20-carbon eicosatrienoic acid. The next step involves desaturation and produces eicosatetraenoic acid, the same intermediate step as the regular pathway. The final step is also the same and produces EPA via desaturation.

DHA Bio-synthesis

• DHA is found in phospholipid membranes of brain, sperm and retina cells. Similar to EPA, DHA biosynthesis occurs in the liver and includes additional steps to the EPA pathway. EPA is elongated to 22-carbon compound DPA, which is further elongated and desaturated to form a 24-carbon and 6--double bond compound. This compound is then oxidized in the final step, which produces DHA. While desaturation and elongation occur in the endoplasmic reticulum of cells, the final oxidation step occurs in microbodies called peroxisomes.