Antioxidants enhance the immune system’s defense against the diseases caused by free radicals. They include Vitamins A, C and E and selenium, and we have been told they may help prevent cancer, heart disease and even such neurological conditions as Alzheimer’s.

Naturally occurring chemicals, antioxidants are found in fruits and juices, made into supplements, and even added to make-up.

But adding extra antioxidants to our diet gives no benefit. You can eat as many blueberries – or whatever the antioxidant-containing food du jour is – as you like and it won’t stop you getting these illnesses. And loading up with supplements may be bad for your health.

Some antioxidants are produced by the body and some by plants, and so they can be derived from the diet. Their job is to combat free radicals – highly reactive molecules formed as a natural by-product of cellular activity. Free radicals are also created by exposure to cigarette smoke, strong sunlight, and breathing in pollution.

These aggressive chemicals present a constant threat to cells and DNA. We know they can lead to cell damage, cancer, diabetes and cardiovascular problems. Free radicals have also been implicated in everything from strokes to Parkinson’s and Alzheimer’s.

Antioxidants stop the chain reactions triggered by free radicals that can damage and destroy cells. So it may seem entirely reasonable that it would be a good thing to eat and drink more antioxidants to boost the supply – or even rub them into your skin. But this is by no means the case.

You might have seen some antioxidant- containing products labeled with a number, usually in the thousands. This is the oxygen radical absorbance capacity (ORAC) number.

It compares the antioxidant with a standard substance called trolox – itself an antioxidant. Cranberries, for example, have an ORAC level of 8,983, which is related to the number of molecules of trolox that would have the same antioxidant strength. Taken in isolation, the number is pretty meaningless, but it makes it possible to compare different foods. So theoretically, the higher the ORAC number, the better the food.

Although there is evidence that antioxidants may have an effect on cancers, much of it is based on experiments on free radicals in cells cultured outside the body, in labs

In reality, beyond a certain point, there is no benefit. In 2008, a study of nearly 15,000 men showed no benefits from Vitamin C and E supplements. There is no recommended daily amount of antioxidant consumption. And although there is evidence that antioxidants may have an effect on cancers, much of it is based on experiments on free radicals in cells cultured outside the body, in labs.

So if antioxidants are good for us, why doesn’t eating more of them have an even more beneficial effect? We know that people with poor diets are more prone to a host of diseases, and that those who eat a balanced diet with at least five fruits and vegetables a day, take exercise, and other very mundane things such as that, have the best chance of not becoming ill. But trials where people have consumed higher than usual levels of antioxidants by taking supplements have found that, if anything, they have a negative impact on health.

A Cochrane Review published last month, which looked at the results of hundreds of individual studies, found that current evidence does not support the use of antioxidant supplements in the general population or in patients with various diseases.

And when the review looked at the mortality rate over 78 randomized clinical trialsfor a range of conditions and using various antioxidants, those consuming antioxidants were 1.03 times more likely to die early.

Another clinical trial last month showed that antioxidant supplements don’t slow down the progression of Alzheimer’s. Two 1994 clinical studies showed a possible increase in lung cancer when taking antioxidants.

Almost all things are poisonous in large enough quantities – even water, though you would have to drink an awful lot to kill you. Similarly, the amounts of antioxidants found in foods are relatively small, so it would be difficult to overdose. Fruit has plenty of other benefits – vitamins that are crucial for healthy functioning and fibre for good digestion, but, like everything, you can consume too much. Excessive consumption may cause damage to the enamel of the teeth or stomach problems.

It is only the excessive consumption of antioxidants through unnecessary diet supplements that could cause any concern.

Using antioxidants on the skin, rather than eating them, may have benefits. Clinical trials have shown that they provide considerable protection against the formation of free radicals in the outer layers of skin when added to sunscreens.

How can we avoid cancer, heart disease, diabetes and the like? Don’t smoke, don’t drink to excess, eat a sensible, balanced diet, including a good mix of fruit and vegetables, and don’t get fat. It’s boring, but true. We know for a fact that the big killer diseases are caused by unhealthy lifestyles.

It would be lovely if eating blueberries or popcorn would somehow counteract a lifetime of abuse, but it’s just not going to happen. And no matter what you do, you can get ill anyway.