Scientists studied the effects of healthier living in 1,260 men and women aged 60 to 77 considered to be at risk of developing dementia due to factors such as their cardiovascular health.
Participants were split into two groups, one of which received an improvement programme including nutritional guidance, physical exercise, mental training, social activities and heart health management.
After two years, these participants performed significantly better in a comprehensive mental ability test than the other group, which received regular health advice.
They also did better in tests of memory, mental processing speed and executive function.
Lead researcher Professor Miia Kivipelto, from the Karolinska Institute in Sweden, said: "This is the first randomised control trial showing that it is possible to prevent cognitive decline using a multi-domain intervention among older at-risk individuals."
The findings were presented at the Alzheimer's Association International Conference in Copenhagen, Denmark.