Existing drugs taken by thousands of people for another health condition may protect against , a study suggests. researchers found that people who took HIV drugs called NRTIs were 6-13% less likely to develop . They are now calling for the drugs to be tested as a way to prevent the condition in clinical trials.

Study leader Dr Jayakrishna Ambati, from the University of Virginia, said: "It's estimated that over 10 million people around the world develop Alzheimer's disease annually. Our results suggest that taking these drugs could prevent approximately one million new cases of Alzheimer's disease every year."

NRTIs, or nucleoside reverse transcriptase inhibitors, are used to prevent the HIV virus from replicating inside the body.

Dr Ambati and his team investigated whether the drugs' effects on the meant they could also reduce risk of developing Alzheimer's.

They reviewed data from more than 270,000 patients aged at least 50 and analysed how many went on to develop Alzheimer's disease.

After adjusting for other factors, those who were taking NRTIS appeared to be significantly less likely to receive a diagnosis.

However, other types of HIV medications did not appear to have the same effect.

Dr Ambati's team has also developed another drug, K9, which works in a similar way, by blocking the activation of inflammasomes, which are important agents of the immune system.

He added: "This drug is already in clinical trials for other diseases, and we plan to also test K9 in Alzheimer's disease."

The findings were published in Alzheimer's & Dementia: The Journal of the Alzheimer's Association.