Dementia is the second leading cause of death in Australia and almost 500,000 people have the disease.

About 40 per cent of cases are linked to 12 risk factors, such as high cholesterol and obesity, that can be affected by diet and exercise - habits that tend to set by middle age.

"The emerging evidence is showing these risk factors for dementia actually span across a lifetime ... and can potentially be targeted earlier," Monash researcher Dr Amanda Cross told AAP.

The three-year trial will look at people aged 45 to 65 who have two risk factors, to see how they respond to regular check-ups with a nurse, as well as an app that tracks their health.

People who have a family history of dementia plus one other risk factor will also be able to participate.

"The primary outcome is to look at the risk factors for dementia and reduce them," Dr Cross said.

Dr Cross is recruiting 500 patients across 34 GP clinics in metropolitan and regional Victoria and NSW to take part.

The patients will initially be given an individual report outlining their risk.

One group will also do a motivational interview with a nurse followed by appointments every three months for a year and two more annual check-ups.

They'll be able to use an app developed in conjunction with the CSIRO.

A second group will receive a booklet about reducing their risk and a GP referral.

Dr Cross says if successful, the trial could improve dementia prevention in middle age.

"We'd love to see it integrated into primary care more globally," she said.

While dementia is usually associated with elderly people, it's estimated there are about 30,000 Australians under 65 who have the disease.

The Holistic Approach in Primary Care for Preventing Memory Impairment and Dementia (HAPPI MIND) is currently recruiting participants.

Australian Associated Press