Free Radicals

Central to the understanding of the health benefits of olive oil are the free radicals. These are highly reactive and unstable chemical compounds.

Diagram courtesy of Javier Pereda

Most organic reactions involve the formation of free radicals and this is the case in the human body. The reactivity of free radicals is moderated by anti-oxidants, and when there is a deficiency of anti-oxidants, or a surplus of pro-oxidants the cell function is disturbed and it may even die. This results in the condition of oxidative stress. The diagram above shows how many of our activities can create this situation of imbalance between free radicals, pro-oxidants, the substrates available for oxidation (peroxidisable substrates) and anti-oxidants.

The function of anti-oxidants is similar to the one we all know about in our own olive oil where the anti-oxidants limit the peroxide value. Peroxides are formed during oxidation of triglycerides which is prevented by the presence of anti-oxidants.

Pro-oxidants comprise free radicals which can be triggered by contaminant substances, smoking, ion radiation, some heavy metals, intense physical activity and oxygen.

The olive is a fruit (really a drupe) which is exposed to air, unlike the seeds from which many other vegetable oils are extracted. The relatively high levels of anti-oxidants in olives is probably a result of the continuous exposure to air and the need to develop defense mechanisms to prevent oxidation.

Amongst the anti-oxidants present in olive oil are ?-tocopherol (vitamin E), ?-carotene (vitamin A) and phenols.


Some of the most important phenols present in extra virgin olive oil are oleuropein (which gives olive oil its bitterness), hydroxytyrosol, pherulic acid and caffeic acid. They contribute to the stability of olive oil and the health benefits by preventing peroxidation. 

Hydroxytyrosol inhibits the aggregation of platelets in the blood, an important factor in the formation of artherosclerotic plaque, and is anti-inflammatory. Oleuropein encourages the formation of nitric acid, which dilates the blood vessels and has a strong anti-bacterial effect.