Arachidonic Acid

What Is Arachidonic Acid?

Arachidonic acid (AA) is a 20-carbon polyunsaturated omega-6 fatty acid with four cis double bonds (20:4, n-6). It is synthesized in the body from linoleic acid through successive desaturation and elongation reactions, but is also obtained directly from animal-based foods. AA is a major component of cell membranes, particularly in the brain, muscles, and liver, where it constitutes a substantial fraction of phospholipid fatty acids.

Although arachidonic acid has a reputation primarily for driving inflammation — owing to its role as a precursor to pro-inflammatory eicosanoids — it performs numerous essential physiological functions and is conditionally essential during rapid tissue growth, particularly in infants.

Key Functions

• Eicosanoid synthesis: AA is the primary substrate for cyclooxygenase (COX) and lipoxygenase (LOX) enzymes, generating prostaglandins (PGE2, PGI2), thromboxane A2, and leukotrienes. These molecules regulate inflammation, platelet aggregation, vascular tone, and immune responses. Non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and aspirin act by inhibiting COX enzymes that process AA.
• Neurological development: AA is critical for brain and retinal development in infants, concentrated in synaptic membranes and gray matter. Along with DHA, it is added to infant formula in most countries based on evidence supporting cognitive and visual development.
• Muscle function and hypertrophy: AA in skeletal muscle membranes plays a role in mechanosensing and exercise-induced muscle protein synthesis. Some research suggests AA supplementation may enhance resistance training adaptations, though evidence remains preliminary.
• Cell signaling: Released from membranes by phospholipase A2, free AA acts as a second messenger, regulating ion channels, gene expression, and apoptosis.

The physiological role of AA-derived eicosanoids is not purely harmful: prostaglandins protect the gastric mucosa, maintain renal blood flow under stress, and facilitate normal immune responses. Pathology arises from chronic overproduction relative to anti-inflammatory counterbalance.

Food Sources

AA is found exclusively in animal-derived foods:

• Egg yolk: approximately 70–80 mg per large egg
• Poultry (chicken, turkey): approximately 60–150 mg per 85 g serving
• Red meat (beef, pork): approximately 50–120 mg per 85 g serving
• Organ meats (liver): among the highest sources, up to 300 mg per 85 g serving
• Fish (salmon, sardines): moderate amounts alongside EPA and DHA

Typical Western dietary intake of AA is approximately 100–500 mg/day. Vegans and vegetarians obtain no preformed AA and rely entirely on endogenous conversion from linoleic acid, resulting in lower but generally adequate plasma AA levels.