The discovery could prompt the discovery of drug treatments to help those at highest risk.

This protein it produces plays a role in the growth of blood vessels. but too much of it may increase stroke risk.

Writing in the journal Nature Genetics, the scientists said people with certain forms of a gene called PDE4D may be most at risk.

Proteins from a similar “family”, called phosphodiesterase (PDE), are linked to other illnesses, such as asthma, inflammation and even erectile dysfunction.

This suggests that it may be possible to develop a drug to block the effects of the gene - the breakthrough impotence drug Viagra already works by targeting another member of the PDE family.

Solveig Gretarsdottir and colleagues at a company called deCode Genetics in Reykjavik believe this gene is associated with an increased risk of stroke.

They carried out DNA tests on over 1,700 people in Iceland, half of whom had suffered strokes.

The Icelandic population is generally regarded as the best testing ground for geneticists.

This is because the gene pool is relatively pure. Unlike most other countries, there has been little immigration since the first Vikings arrived almost 1,000 years ago.

Scientists working on this latest study say they have identified genetic differences between those people who have had strokes and those who have not.

These differences centre on the gene PDE4D, located on chromosome 5.

They have found that three different isoforms of the gene were expressed at lower levels in people who had strokes.

Isoforms are groups of proteins that are produced by a gene.

They also found different combinations of genes in regions of chromosome 5 flanking the PDE4D gene in people who had strokes.

It is already known that this gene provides the coding which enables a protein called a phosphodiesterase to work.

Stroke risk

But the Icelandic scientists believe that too much of it may increase the risks of - furring up of the arteries.

This causes the arteries to narrow, which can trigger a stroke.

“We propose that PDE4D is involved in the pathogenesis of stroke, possibly through atherosclerosis, which is the primary process underlying ischemic stroke,” the scientists said.

They believe that blocking the protein in people with these potentially problematic forms of the PDE4D gene could protect them against stroke.

There are already drugs available to do this. These so-called phosphodiesterase inhibitors are used to treat asthma, inflammation and erectile dysfunction, with Viagra probably the best known.

However, much further study is needed before these drugs could be used to treat people who may have a high risk of having a stroke.

Viagra, for one, has potentially serious side effects if taken by men with underlying health problems.

The drug, used by millions of men, slowed the increase in the strength of heart by half.

The Johns Hopkins University study, published in , found the drug acted as a “brake”.

However, UK heart experts warned men with heart conditions should talk to their doctor about taking the drug to ensure they use it safely.

Mixing this drug with other heart medicines or taking it if you have angina without advice from a health professional or GP can be dangerous for heart patients Dr Charmaine Griffiths, British Heart Foundation

Viagra, also known as sildenafil, helps men with erectile dysfunction by making genital blood vessels expand in order to maintain an erection.

The Johns Hopkins team have previously shown Viagra can block the short-term effects of hormonal stress in the heart in mice.

But it had been thought to have little direct effect on the human heart.

This study looked at 35 men and women, with an average age of 30 and no previous signs of coronary artery disease.

They were all given an injections of an adrenaline-like chemical called dobutamine, which increases heart rate and pumping strength in the same way as emotional or exercise stress, or heart failure.

They were then randomly assigned to either take 100mg of Viagra or a dummy pill before receiving a second injection. Heart function was measured before and after each jab.

After the first injection of dobutamine, the force of heart contraction increased by 150% in both groups.

In the dummy pill group, the same effect was seen after the second injection.

However, in the group treated with Viagra the increased heartbeat was slowed by 50%, resulting in a smaller increase in blood flow and blood pressure generated by the heart in response to chemical stimulation.

No adverse side effects on the heart were seen.

Viagra helps maintain erections by blocking the action of an enzyme which prevents the relaxation of blood vessels in the penis.

The same enzyme, called phosphodiesterase 5 (PDE5A), is also involved in the breakdown of a key molecule, cyclic GMP, which helps control stresses and limit heart enlargement.

Heart warning

Professor David Kass, the cardiologist who led the study, said: “Sildenafil effectively puts a 'brake' on chemical stimulation of the heart.”

He added: “Knowing more about the effects of sildenafil on heart function will allow for safer evaluation of its use as a treatment for heart problems.

“Until now, it was widely thought that drugs like sildenafil had no effects on the human heart and that its only purpose was vasodilation in the penis and the lungs.”

He said further studies should be carried out to investigate Viagra's immediate and long-term effects on the heart.

Dr Charmaine Griffiths, from the British Heart Foundation, said: “Viagra has been a real advance in treating impotence, which affects nearly half of men between 40 and 70 years old.

“The findings that Viagra affects blood pressure is not surprising - before it was known as a successful treatment for impotence, it was actually being researched for lowering effects on blood pressure.”

But she added: “If you have a heart condition you should check with your doctor before taking Viagra.

“Mixing this drug with other heart medicines or taking it if you have angina (heart pain on exercise) without advice from a health professional or GP can be dangerous for heart patients.”

The drug's maker Pfizer says it is submiting an to European regulatory authorities to clear it for sale in pharmacies.

An estimated 27 million men have already used the little blue pill for erectile dysfunction on prescription.

Medics said a change would be welcome but might mean other linked diseases were missed with no health check ups.

Ups and downs

Often, men with erectile dysfunction have underlying health problems such as diabetes, which can be spotted by their GP at the time they come for an anti-impotence prescription.

“If men can buy Viagra and rival anti-impotence drugs over-the-counter without a prescription, this opportunity is missed,” said Dr David Ralph from the Institute of Urology at University College London.

But there would be benefits too, he said, such as combating the problem of Viagra sold illegally on the internet from unknown sources, which may be fake and if taken with some medicines could be fatal.

He said it would be safe to buy over-the-counter provided the pharmacist did the necessary checks to ensure the medication was suitable for the patient.

factor

It might also be a more attractive option to men as going to see the GP about sexual problems can be embarrassing, he added.

But he cautioned: “There is more to sexual relations than an erection. There may be other problems.”

Viagra works by relaxing the blood vessels in the penis. This allows blood to flow into the penis causing an erection.

However, the drug is not an aphrodisiac and does not increase sex drive.

It is licensed only as a treatment for men who have been diagnosed by a doctor as having impotence.

Also, some men, such as those with severe heart disease or low blood pressure, should avoid it because of possible risks and side effects.

Viagra is not licensed for use in women and its safety in women has not been established.

A Pfizer spokesman said: “As with many of our products, Pfizer has routinely evaluated a number of options including different formulations, new indications, over-the-counter and continues to do so.”

He added that despite speculation there were no plans to pursue a spray version of the drug.

The exercises were found to help men with erectile as much as taking in Viagra.

The researchers say the findings mean men have an alternative to drug therapy.

For around 50 years, women have been advised to perform pelvic floor exercises to strengthen their muscles for childbirth.

The pelvic floor is a “hammock” of muscles which support the bowel and bladder.

Pelvic floor, or Kegel, exercises involve clenching the muscles you would use to prevent yourself urinating.

This latest research indicates it is also important for men to maintain the muscle tone and function of their pelvic floor muscles with the exercises.

Home exercises

The team from the University of the West of England in Bristol studied 55 men with an average age of 59 who had experienced erectile dysfunction for at least six months.

The men, all patients at the Somerset Nuffield Hospital, Taunton, Somerset, were given five weekly sessions of pelvic floor exercises and assessed at three and six months, and asked to practise the exercises daily at home.

It was found 40% of the men regained normal erectile function - some of who had severe erectile dysfunction, and another 35% showed some improvement.

Two thirds of the men had said they also had problems with urination. These improved significantly after they began the exercises.

Dr Grace Dorey, a specialist continence physiotherapist who carried out the research, told BBC News Online: “The exercises were found to be equally as effective as taking Viagra.

“Pelvic floor exercises improve function in a physical way, in a more natural way.

“Men should be doing preventative exercise. It really is use it or lose it.”

She said men should be exercising their pelvic floor exercises from puberty onwards.

Strength

A spokesperson for the Impotence Association said: “The value and effectiveness of pelvic floor exercises should not be underestimated when the management of sexual problems such as impotence and premature .

“The exercises are thought to strengthen the muscles that surround the penis and improve the blood supply in the pelvis, which is an important factor in relation to erectile dysfunction.”

The Impotence Association helpline number is 0208 767 7791.

One of the images carries the strapline “Your penis thinks you should stop smoking” to highlight the risk of impotency.

Ministers say fears about fertility and attractiveness are stronger motivators for young people to quit than health.

A survey suggests one in two smokers would quit to improve their sex appeal.

The NHS Smoking Helpline questionnaire also revealed that more than two-thirds of young men and women believe smoking makes them less attractive.

Half of men said they associated smoking with wrinkles, bad skin and less enjoyable kissing.

Another of the ads shows stark images of the effect of smoking on women's appearance and attractiveness to men, with messages such as “If you smoke, you stink”, “Minging teeth” and “Cat's bum mouth”.

Websites called “Staying Hard” and Ugly Smoking” will also be launched, alongside a sticker campaign in pub and club toilets.

Public Health Minister Caroline Flint said: “This latest series of adverts marks a new and exciting route for the campaign.

“A key part of our drive to reduce overall smoking prevalence is getting the message to harder-to-reach young adult audiences.

Hard-hitting

“We know 70% of smokers want to stop smoking; however, with younger people, fears about attractiveness and fertility can be a stronger motivation to quit than fears about health.

“It is hoped that the hard hitting messages in this new campaign will make young people quit smoking for good.”

Smoking can damage your teeth

Smoking increases the risk of erectile dysfunction by around 50% for men in their 30s and 40s and up to 120,000 men from the UK in this age group are impotent as a direct result of smoking, experts estimate.

Clive Gingell, chairman of the Sexual Dysfunction , said: “By making men aware of how smoking can affect their sexual in middle age, hopefully this new campaign should provide men with an additional and compelling reason to quit.”

Dr Bav Shergill, from the British Skin , said: “Giving up smoking can not only add years to your life, it also adds years to your appearance and can help stop premature aging before it's too late.”

However, Simon Clark, director of the smokers' lobby group Forest, said: “To try and suggest that smoking is a major cause of impotence is a scare tactic.

“It's nasty because it is not only setting out to de-normalise smoking, but really to make smokers feel incredibly guilty about their habit.”

Dr Moloy Prakash Sahu, who worked at the Wellman Clinic, 57 Harley Street, for a year, faced several .

These ranged from providing treatment without medical justification to “irresponsible prescribing”.

The General Medical Council said his practice was “less than satisfactory” but did not amount to serious professional misconduct.

'Boost'

The four-day hearing was held after three patients at the clinic complained to the GMC.

It heard that the average patient was given a three-month course of impotence treatment made up of vitamins, creams and washes, costing 1,500 to 2,000 - many of which were “useless if not dangerous”.

One of the three was prescribed a drug which, mixed with an drug he was already taking, could have proved fatal.

That patient was also treated for a condition he did not suffer.

Dr Sahu denied it was “irresponsible” to prescribe the drug Yohimbin to one man, saying: “He had erectile problems and it is a medicine you can give.”

He also said his employers at the clinic insisted vitamin injections be given as a matter of policy.

Dr Sahu admitted the “harmless” injection was a placebo and that he never told patients it had no medical justification, but said it could give a patient “a bit of a boost”.

'Less than satisfactory'

Dr Sahu, of , east London, worked at the clinic as medical officer between July 2000 and June 2001.

He said he became “dissatisfied” and quit the post because the clinic was badly managed and poorly equipped.

Dr Sahu was cleared of failing to ensure his patients were given sufficient information about their conditions, and failing to keep proper drug records.

The doctor was also acquitted of treating patients without the required expertise and failing to make sure patients gave proper or informed consent for treatment.

A number of other allegations were withdrawn following legal .

The hearing's chairman John Shaw said: “These taken together did not cross the threshold of serious professional misconduct.

“The committee therefore finds you not guilty of serious professional misconduct.”