Eating fish can help to repair some of the damage inflicted on the body by smoking, a study suggests.

Researchers in the Irish Republic say amino acids in fish stop arteries from hardening and could help to cut deaths from heart disease and stroke.

Smoking is a major cause of endothelial dysfunction - a condition where the arteries do not dilate as they should.

The best therapy for smokers is to stop smoking Professor David Bouchier-Hayes

It is one of the earliest signs of atherosclerosis or the narrowing of arteries. This is a major cause of heart attacks and strokes.

Professor David Bouchier-Hayes and colleagues at Beaumont Hospital in Dublin examined the arteries of a group of smokers and a group of non-smokers by applying a tourniquet to their forearms.

Using ultrasound scans, they found that while the arteries of non-smokers could dilate those of smokers did not.

Fish supplement

However, this changed if the smokers had taken just 1.5 grammes of taurine - equivalent to one serving.

This is an amino acid which exists naturally in all kinds of fish.

The study also found that vitamin C had a similar though less pronounced effect on the blood vessels of smokers.

The doctors said the findings could help patients with endothelial dysfunction.

However, they stressed that eating fish should not be regarded as a possible antidote to smoking.

"We're not trying to find a therapeutic treatment for smoking, because we believe that the best therapy for smokers is to stop smoking," said Professor Bouchier-Hayes.

"Nonetheless, smokers provide a good clinical model for treatment of endothelial dysfunction."

In a second study, doctors in the United States found that the drug allopurinol, which is used to treat gout, can also dramatically improve smokers' endothelial function.

Dr William Haynes, from the University of Iowa College of Medicine, who led the study, said the results were the first to show that allopurinol could have "rapid and substantial endothelial effects in smokers".

Health problems

Clive Bates, director of anti-smoking group Action on Smoking and Health, welcomed the studies. But he warned that smoking caused a range of other serious health problems.

It is important for people to stop smoking to reduce their risks of coronary heart disease Alison Shaw, British Heart Foundation

"The significance of this goes well beyond smoking. Obviously what's happening here is that something is compensating for, or preventing the damage smoking causes to one aspect of the circulatory system.

"Smoking has many other impacts on the heart - things like thickening of the blood and increased cholesterol levels. It causes 50 different diseases, including cancer and respiratory illness.

"The best way of looking at this is as something that could have very important consequences for the treatment of heart disease, but shouldn't be seen as a magic pill that somehow makes smoking safe. No-one in their right mind would think that."

Alison Shaw, of the British Heart Foundation, said: "These two new studies are small but interesting and show that in a small number of people vitamin C, taurine and the gout drug allopurinal have a positive effect on the lining of the coronary arteries.

"We know of the link between smoking and the damage it does to blood vessels that subsequently contributes to coronary heart disease.

"However, more research is needed on what exactly benefits or damages the function of the lining of the coronary arteries.

"Until then, as the researchers mention themselves, it is important for people to stop smoking to reduce their risks of coronary heart disease."

The studies are published in Circulation, the journal of the American Heart Association.