Insurance shows a link between Viagra prescription and a lower chance of the disease

But new research shows that it might not just be helpful in the bedroom - there's a suggestion that Viagra may also help to prevent Alzheimer's disease.

It was originally developed to treat angina - although it didn't make it through trials - and there's some evidence it could help treat malaria.

Tadalafil, a similar drug to Viagra, has been proposed as a heart failure treatment.

A paper in Nature Aging has expanded its potential further, using records from insurance claims to examine the link between Viagra and Alzheimer's disease.

The researchers, who are based in the US, examined the insurance records of 7.23 million people, alongside genetic and other biological data.

They looked through the data to pull out indicators of Alzheimer's disease, and then examined the relationship between these indicators and over 1600 prescribed medicinal drugs.

Viagra had the highest link to lower chance of Alzheimer's, with its prescription being associated with a 69 per cent reduced risk of the disease.

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The researchers point out that while this link is significant, it doesn't establish causality: it may be that Viagra prevents Alzheimer's, or it may be that people who have fewer biological precursors to Alzheimer's are also more likely to receive a Viagra prescription.

There could also be other confounding factors at play. Sildenafil, for instance, is more likely to be prescribed to wealthy people, and wealthy people are also less likely to get Alzheimer's disease.

The sample size of Viagra users was also - unsurprisingly - mostly male.

"Taken together, the association between sildenafil usage and decreased incidence of AD [Alzheimer's disease] does not establish causality or its direction," write the researchers in their paper.

"Our results therefore warrant rigorous clinical trial testing of the treatment efficacy of sildenafil in patients with AD, inclusive of both sexes and controlled by placebo."