Men on Viagra may reduce Alzheimer's risk - study

Men who take drugs for erectile dysfunction, such as Viagra, may reduce their risk of Alzheimer's disease, a study suggests.

In research on more than 260,000 men, those taking the drugs were 18% less likely to develop the dementia-causing condition.

But more research is needed to prove that the drugs are causing the effect.

Two new Alzheimer's drugs have shown huge promise at slowing the pace of the disease in its earliest stages.

But scientists are also continuing to look for existing drugs that could prevent or delay it developing in the first place.

Drugs like Viagra were originally designed to treat high blood pressure and angina. They work by acting on a cell-signalling messenger that may also be linked to memory.

They are also known to affect brain cell activity, and research in animals suggests they have some protective effect on the brain.

In the new study in Neurology, researchers from University College London looked at prescription records of thousands of men with erectile dysfunction, comparing those who had been given the drugs with those who hadn't.

Over the following five years, they found 8.1 cases of Alzheimer's per 10,000 person years in the group prescribed the drugs, and 9.7 cases in the group not taking them.

Men who had been issued the most prescriptions for erectile dysfunction drugs were least likely to develop Alzheimer's, suggesting regular use of the drug could have a greater impact on the disease.

The researchers say their study doesn't show that the drugs themselves were reducing people's risk of Alzheimer's, but could point to a new avenue of research.

Lead author Dr Ruth Brauer said: "More research is needed to confirm these findings, learn more about the potential benefits and mechanisms of these drugs and look into the optimal dosage."

The researchers also want to run a trial in women as well as men, to see if the drug has any impact.

There are many factors which could be causing the disease. The study adjusted its findings for some of them, including age, underlying health conditions, other medicines taken and whether the participant was a smoker.

"This study does not conclusively prove that erectile dysfunction drugs reduce Alzheimer's risk but provide good evidence that this type of drug is worth further study in future," said Prof Tara Spires-Jones, from the University of Edinburgh, and president of the British Neuroscience Association.

Dr Francesco Tamagnini, neurophysiologist at the University of Reading, said it was "a great study", but more hard evidence on how the drug affected the brain was needed.

"It could be that it exerts a therapeutic effect directly affecting neurons (if the drug is able to cross the blood brain barrier) and/or by increasing blood flow, but both these hypotheses need to be tested," he said.