Participants were assessed for three risk factors: high blood pressure, type 2 diabetes, and smoking. They were then followed for about three decades, with an average follow-up of 26 years.

Those who had none of the three risk factors lived without developing dementia almost 13 years longer than those who had all three.

Those with no diabetes, no high blood pressure and who did not smoke at the start of the study had an average of 30.1 more years free of dementia, the study found.

Meanwhile, those with one risk factor had an extra 26.3 years, those with two had 21 years, and those with three had just over 17 years.