Omega3 fatty acid

Omega-3 fatty acids, also referred to as omega-3 oils, ω-3 fatty acids or n-3 fatty acids, are a family of polyunsaturated fats (PUFAs) characterised by the presence of a double bond three carbon atoms from the terminal (methyl) end of the molecule. Widely distributed in nature, they are essential components of animal lipid metabolism and play vital roles in human physiology, particularly in brain function, cardiovascular health and cellular structure.
Three omega-3 fatty acids are directly involved in human biological processes: α-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). ALA is chiefly obtained from plant sources, whereas DHA and EPA are found predominantly in marine algae and the fish that consume them. Most animals cannot synthesise ALA and must acquire it from dietary sources, although humans can convert limited quantities of ALA into EPA and DHA, a capability that declines with age.

Sources and Nutritional Role

Plant-based oils such as flaxseed, walnut, hempseed and edible seeds provide ALA. Marine sources of EPA and DHA include fatty fish and fish oils, while algal oil serves as a non-animal alternative. Marine phytoplankton constitute the primary source of EPA and DHA in ocean ecosystems, with fish accumulating these fatty acids through the food chain.
Omega-3 fatty acids contribute to membrane structure, neurological development, inflammation modulation and lipid regulation. DHA is particularly abundant in the human brain and retina, reflecting its significance in neural and visual development.

Chemical Structure and Nomenclature

Omega-3 fatty acids are named according to the position of the first double bond nearest the methyl end of the carbon chain. The term “omega-3” denotes that the first double bond begins at the third carbon from this end. The notation n-3 or ω-3 represents the location of this double bond relative to the highest-numbered carbon of the chain.
For example, ALA (18:3 n-3) contains 18 carbon atoms and three cis double bonds, situated at carbons 9, 12 and 15 when counted from the carboxyl end. EPA (20:5 n-3) and DHA (22:6 n-3) have progressively longer chains and additional double bonds. All naturally occurring double bonds in omega-3 fatty acids adopt the cis configuration and are separated by methylene groups, giving rise to highly flexible and reactive structures.
Unsaturated fatty acids are susceptible to oxidation, leading to rancidity in foods. Omega-3 fatty acids, being highly polyunsaturated, are particularly prone to this process. Experimental research indicates that replacing certain hydrogen atoms in bis-allylic positions with deuterium increases resistance to oxidation and reduces lipid peroxidation.

Forms and Biochemical Processing

Omega-3 fatty acids occur naturally in two major forms:

• Triglycerides, where three fatty acids are esterified to glycerol.
• Phospholipids, in which two fatty acids are attached to glycerol via a phosphate-containing head group.

Commercial supplements may contain EPA and DHA as free fatty acids, methyl esters or ethyl esters. In the body, ALA is enzymatically converted into EPA and subsequently DHA by elongase and desaturase enzymes. However, the efficiency of this conversion is limited and varies among individuals.

Mechanism of Action

The term essential fatty acids emerged in the 1920s when George and Mildred Burr demonstrated that certain fatty acids are indispensable for growth and survival. Humans lack the necessary desaturase enzymes to introduce double bonds at the n-6 and n-3 positions, making dietary intake essential.
Omega-3 fatty acids influence inflammation, neural function and cardiovascular physiology. In 1964, research showed that enzymes convert omega-6 arachidonic acid into prostaglandin E₂, a mediator of inflammatory responses. Omega-3 fatty acids, particularly EPA, can modulate the production of inflammatory eicosanoids, contributing to their therapeutic interest.

Health Effects and Supplements

Omega-3 fatty acids have been widely studied for their potential health benefits. Evidence shows:

• Only limited or inconclusive benefits in preventing cancer, all-cause mortality or major cardiovascular events.
• Modest reductions in blood pressure and significant lowering of triglyceride levels, particularly when using prescription-grade formulations.
• Possible improvement in cardiovascular risk in certain clinical contexts.

The US Food and Drug Administration in 2004 authorised a qualified health claim stating that EPA and DHA may reduce the risk of coronary heart disease, though evidence was not conclusive. Canadian regulatory agencies recognise DHA’s role in early neural and visual development.
Industrial diets, particularly those dominated by shelf-stable processed foods, tend to lack sufficient omega-3 fatty acids due to the susceptibility of these fats to oxidation during processing and storage.

History

The scientific recognition of omega-3 fatty acids began with the Burrs’ discovery of essential fatty acid deficiency in 1929. Interest expanded dramatically during the 1980s as research highlighted their physiological significance. Historically, whole-food diets provided adequate omega-3 intake, but modern dietary patterns and industrial processing have reduced the availability of naturally occurring ALA, EPA and DHA.

Chemistry and Stability

Omega-3 molecules vary in chain length and degree of unsaturation. Short-chain omega-3 fatty acids have up to 18 carbons; long-chain forms such as EPA and DHA have 20 or more. Their multiple cis double bonds increase membrane fluidity but also render them vulnerable to free-radical attack. Protective strategies, such as deuteration, aim to enhance oxidative stability.

Lists and Classification

Common omega-3 fatty acids in nature include:

• ALA (18:3 n-3) – plant-derived, essential nutrient.
• EPA (20:5 n-3) – marine-derived, precursor to anti-inflammatory mediators.
• DHA (22:6 n-3) – critical for neural and retinal development.