A highly controversial paper just published in the science journal Nature claims that free radicals have been given an unwarranted bad press. “Patients may be using expensive antioxidant drugs based on completely invalid theories,” says Dr Tony Segal, an immunologist at the Centre for Molecular Medicine at University College London. “Our research suggests that all theories about the role of oxygen free radicals in disease must be re-evaluated.”

It’s an astounding claim, but what is it based on? For years experts have believed that as well as damaging tissue, free radicals are also vital to the immune system’s fire power. As Dr Segal explains: “The conventional theory says that when the body senses any kind of microbial attack the immune cells such as neutrophils release free radicals to kill off the invaders.” Because they are seen as being so efficient at destroying hardy bacteria, claims Segal, it is widely believed that free radicals can also destroy healthy tissue.

However, when Segal ran an experiment to test the killing power of free radicals, he found they were not the weapons of bacterial mass destruction that everyone had thought.

“We found that although the cells were working properly in every other way, including pumping out free radicals,” he says “the bacteria were untouched.” In other words, free radicals were not attacking bacteria at all. “This finding at once calls into question the notion that they are damaging tissue and that we need antioxidants to deal with chronic infections,” he says.

Not surprisingly, other experts, while admiring the precision of Dr Segal’s study, feel that he is going several steps too far in dismissing free- radical damage.

“What he has effectively shown is that the immune cells are using something else to attack bacteria,” says Dr Nick Lane, a biochemist at University College London, who last year wrote the widely acclaimed book Oxygen: The Molecule that made the World. “But that doesn’t mean that other arms of the immune system aren’t using free radicals. There are also thousands of papers showing that free- radical damage plays a major role in ageing.”

But Dr Segal is unrepentant: “Neutrophils are the most common of the immune system cells. They swamp free radicals, which means that they don’t form a major part of our defences, and that calls for a complete rethink.”

Dr Lane does believe that we have got the free radical/antioxidant story wrong, but in a different way. While he has no doubt that free radicals are responsible for most of the chronic diseases of ageing, he doesn’t believe that antioxidant supplements are the way to deal with them.

“The studies generally show that they are not very effective,” he says.

In a paper published last year in the Journal of Theoretical Biology, he suggests that there is a good reason for this. “One role of free radicals is to sound the alarm. When released by neutrophils and other immune cells, they alert the system to danger,” he says. That’s why the body blocks extra antioxidants from having much effect — damping the free radicals down too much would actually increase the risk of infection.

For the present, one point that everyone agrees on is that eating fresh fruit and vegetables is vital for keeping the immune system fighting fit.