Reactive Oxygen Species (ROS) such as peroxide and superoxide are an inevitable part of our body’s metabolism; they can cause oxidative damage in the body which is a major cause of chronic inflammation and a wide variety of disease conditions.
“The most pressing human health issue is oxidative stress caused by physical and mental stress.”
Prof Peter Molan MBE of the renowned New Zealand honey research unit.
Antioxidants are known to play an important role in combating the oxidative damage ROS causes in the body. The most familiar way in which antioxidants protect human cells is through scavenging for free radicals. However, recent studies have shown that in some cases antioxidants are ineffective in preventing oxidation and have focussed on other mechanisms by which antioxidants provide protection.
Ferrous ions which are free or poorly bonded are known to initiate the formation of free radicals. Put more simply, too much free iron in the body is also thought to lead to oxidative damage to cells, as seen in diseases such as type II diabetes, atherosclerosis and liver disease. This process whereby hydrogen peroxide reacts with free iron leading to damaging radicals is called the Fenton reaction.
What are needed, therefore, are iron-binding antioxidants which can contain excess iron so that it is unable to participate in forming free radicals. Such antioxidants are likely to be more effective, too, than those that simply scavenge for free radicals as they can pre-empt free radical formation rather than attempting to clear free radicals once they are active.
Dr Peter Molan and Helene L Brangoulo looked at various foodstuffs known to be rich in antioxidants – blackcurrant puree, thyme, honeydew and Rewarewa honeys, red wine and orange juice – in order to measure their iron-binding antioxidant capacity. Their experiment simulated oxidative damage to membrane lipids and low density lipoproteins which occur when free iron is present.
The blackcurrants, honeydew honey and red wine were all found to be effective at preventing lipid breakdown by containing ferrous ions. It is thought that the flavonoids in honeydew and blackcurrant may be providing this protection, as bioflavonoids have been seen to help clear excess iron in mice. Flavones, isoflavones, catechins, tannins and anthocyanidins are all flavonoids which may chelate iron.
Molan also compared the antioxidant effect of iron sequestration with the more usual measurement of free radical scavenging. He discovered that orange juice and thyme honey offered no protection against the Fenton reaction, although the thyme honey was more than 3 times as active as other honeys as a free radical scavenger.
If ferrous ions are present and uncontrolled, Molan’s assay found that the rate of oxidative damage was 25 times greater than it would be without the excess free iron. Also, when vitamin C is added to ferrous ions, oxidation may actually increase, so that it becomes a pro-oxidant rather than an antioxidant.
Disorders that may be related to poor iron metabolism include metabolic syndrome, inflammatory conditions such as psoriasis and asthma, and pre-eclampsia. It is well known that high iron levels can be a factor in coronary artery disease, which may lead to heart attack; iron is also found in atherosclerotic lesions. It is strongly implicated in a variety of neurodegenerative diseases and has been found in the plaques characteristic of Alzheimer’s disease.
Low iron blood levels are common in cases of rheumatoid arthritis, but high levels are found in the synovial fluid of arthritic joints, so it seems likely that faulty iron metabolism plays a part in the condition. It is also thought that inadequately controlled iron metabolism may accelerate the ageing process.
Clearly we need antioxidants which can both scavenge free radicals and bind up excess iron and it seems that honey and blackcurrant may offer both kinds of protection.