The price that we pay for life is that our bodies slowly die. This isn’t some deep philosophical reflection but a simple biological fact - the very processes that keep us alive also generate toxic chemicals that can damage and eventually destroy the body’s cells.

One of the most important of these processes is a chemical reaction involving oxygen called oxidation. This is common throughout nature, causing iron to rust, for example, or butter to go rancid. In humans, oxidation is an essential part of normal metabolism, where by nutrients are broken down to be used by the body for energy, growth and repair.

But oxidation also leads to degeneration and ageing. During oxidation, positively and negatively charged particles are formed, known as Reactive Oxygen Species (ROS) or more commonly ‘free radicals’. Within the cells, free radicals break down other chemicals such as fats and proteins, causing destruction that may contribute to problems such as cardiovascular disease, heart attacks, stroke, cancer, cataracts and chronic inflammatory diseases.

Antioxidants may prevent oxidative damage

All this damage doesn’t go unchecked. Many chemicals have an antioxidant effect, preventing oxidation or mopping up free radicals. But although the body produces its own supply of antioxidants, levels drop as we age. In addition, environmental factors such as pollutant chemicals cause oxidation, so speeding ageing and increasing the risk of disease.

Fortunately many foods contain antioxidants and it is easy to take in more simply by improving our diet. However, many studies of antioxidants have found that high doses may be needed for the best effect and antioxidant supplements may provide better protection.

ACE vitamins are antioxidants

Perhaps the best known antioxidants are vitamins and minerals, in particular vitamin A, C, and E. A group of chemicals called carotenoids are especially important. These include provitamin A (or B-carotene) and are found in red, orange and yellow vegetables and fruit (for example, carrots, peppers, mangos and apricots). Lycopene, found in high levels in tomatoes, watermelon and apricots, is another example.

The flavonoids are another important group of antioxidants. Red wine is packed with flavonoids and research has pinpointed these to explain lower rates of heart disease in countries such as France, where red wine intake is higher. Tea contains a type of flavonoid called catechins. Scientists at the University of Kansas, USA, have shown that these are dozens of times more powerful than vitamin E or C. In particular flavonoids may stop oxidative damage to the genetic material or DNA, so protecting the cells against genetic mutations which can trigger cancer. Green tea contains the most catechins, but black tea also has antioxidant effects.

Recent research has shown that antioxidants work together to prevent free radical damage. For example, after vitamin E has neutralised a free radical, it becomes a weak free radical itself. Vitamin C then works on this spent form of vitamin E to recycle it back to normal. Similarly vitamin C must then be recycled by a chemical called glutathione. Antioxidants also need a little help from other micro-nutrients in order to workproperly; these include selenium, copper, magnesium, zinc and manganese.

An answer to ageing?

It’s possible that certain antioxidants may provide better protection than others against particular diseases. But research is still at an early stage and the exact picture isn’t clear. However, there is growing evidence that, in general, antioxidants can hold back the ravages of time.

For example, antioxidants may be the first-ever treatment to have some effect against a common eye disease called age-related macular degeneration or AMD. Researchers have found that a high-dose combination of vitamin C, vitamin E, beta-carotene and zinc slows progression of the condition by about 25% among those people at high risk of advanced AMD. Meanwhile, another carotenoid antioxidant called lutein helps to protect the retina from toxic compounds which are activated by incoming blue light. Not only does lutein help to prevent AMD but it may also hold back ageing of the lens and prevent the formation of cataracts.

Research at the University of California at Berkeley has led to claims for a less well-known antioxidant called alpha-lipoic acid. More potent than vitamins C and E, alpha-lipoic acid is the only antioxidant that can easily move from the blood stream into the brain and so may be useful in preventing damage from a stroke. Another antioxidant that may help keep the brain young is acetyl-L-carnitine. Studies show that acetyl-L-carnitine can delay the onset of age-related cognitive decline (ARCD), a common condition which may be an early form of dementia. People with ARCD experience deterioration in memory learning and other mental functions. When acetyl-L-carnitine was given to people with mild ARCD it led to significant improvements, especially in memory, mood and responses to stress.

An antioxidant called co-enzyme Q10 also looks promising and may slow the progression of diseases such as early-stage Parkinson’s or Huntingdon’s. Scientists believe co-enzyme Q10 works by improving the function of mitochondria, the ‘powerhouses’ that produce energy in cells and protecting vulnerable areas of the brain.

Antioxidants and heart disease

Antioxidants are being extensively studied in heart disease. Oxidation of ‘bad’ cholesterol (low-density lipoprotein, LDL) leads to the build-up of fatty deposits inside arteries called atherosclerosis. Once atherosclerosis has developed, a heart attack will occur if a clot forms in the narrowed artery - a process which also involves oxidation.

People with a high intake of vitamin E have been shown to have a lower risk of coronary artery disease and it may slow the development of atherosclerosis. Vitamin C has also been linked to lower rates of coronary artery disease, while researchers are now looking at whether vitamin A might reduce the risk of heart attack.

Keeping cancer at bay?

Early laboratory studies made researchers optimistic that antioxidants could slow or possibly prevent the development of cancer. But tests among real people have so far shown inconsistent results.

One large trial (The Chinese Cancer Prevention Study) has shown that a combination of beta-carotene, vitamin E and selenium may significantly reduce the risk of both gastric and other cancer. Another Chinese study found men who drank green tea could halve their risk of stomach or oesophageal cancer. The antioxidant lycopene is thought to explain why prostate cancer is relatively rare in southern Mediterranean countries. A study at Harvard Medical School found that foods rich in lycopene, such as tomato sauce, could be linked to lower levels of prostate cancer.

But many other studies have failed to find any effect and some have suggested that antioxidants might even increase the risk of lung cancer in smokers. Researchers from the University of California have pointed out that the situation is very complex and that in some cases, such as when the body is under stress, antioxidants may lose their effect and start to promote oxidation.

Around the world large trials of antioxidants are currently under way. These should help to improve our understanding about how this important group of compounds works. Is it, for example, really the antioxidant action that is preventing disease, or do they act in other ways? The future looks very promising but for now the jury is still out.

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