Researchers from George Washington University in Maryland, followed 2,766 patients who had previously taken part in a three-year diabetes prevention trial for a further 10 years.
In the original study, patients were assigned to lifestyle intervention, metformin or placebo. For the follow-up, they were offered extra lifestyle support.
Diabetes incidence in the 10-year follow-up was reduced by 34 per cent in patients originally given lifestyle advice and 18 per cent in those given metformin.
The researchers say onset of diabetes was delayed by about four years by lifestyle intervention and two years by metformin compared with placebo.
The lifestyle intervention also improved BP and lipid levels.
The researchers said: 'Our results show that a reduction in diabetes cumulative incidence by either lifestyle intervention or metformin therapy persists for at least 10 years.'
They believe further follow-up will provide crucial data for long-term clinical outcomes.